自旋响应催化原位监测

Aqueous-phase oxygen evolution reaction (OER) is the bottleneck of water splitting. The formation of the O-O bond involves the generation of paramagnetic oxygen molecules from the diamagnetic hydroxides. The spin configurations might play an important role in aqueous-phase molecular electrocatalysis. However, spintronic electrocatalysis is almost an uncultivated land for the exploration of the oxygen molecular catalysis process. Herein, we present a novel magnetic FeIII site spin-splitting strategy, wherein the electronic structure and spin states of the FeIII sites are effectively induced and optimized by the Jahn-Teller effect of Cu2+. The theoretical calculations and operando attenuated total reflectance-infrared Fourier transform infrared (ATR FT-IR) reveal the facilitation for the O-O bond formation, which accelerates the production of O2 from OH- and improves the OER activity. The Cu1-Ni6Fe2-LDH catalyst exhibits a low overpotential of 210 mV at 10 mA cm-2 and a low Tafel slope (33.7 mV dec-1), better than those of the initial Cu0-Ni6Fe2-LDHs (278 mV, 101.6 mV dec-1). With the Cu2+ regulation, we have realized the transformation of NiFe-LDHs from ferrimagnets to ferromagnets and showcase that the OER performance of Cu-NiFe-LDHs significantly increases compared with that of NiFe-LDHs under the effect of a magnetic field for the first time. The magnetic-field-assisted Cu1-Ni6Fe2-LDHs provide an ultralow overpotential of 180 mV at 10 mA cm-2, which is currently one of the best OER performances. The combination of the magnetic field and spin configuration provides new principles for the development of high-performance catalysts and understandings of the catalytic mechanism from the spintronic level.

We employed operando soft X-ray absorption spectroscopy (XAS) to monitor the changes in the valence states and spin properties of LaMn1–xCoxO3 catalysts subjected to a mixture of CO and O2 at ambient pressure. Guided by simulations based on charge transfer multiplet theory, we quantitatively analyze the Mn and Co 2p XAS as well as the oxygen K-edge XAS spectra during the reaction process. The Mn sites are particularly sensitive to the catalytic reaction, displaying dynamics in their oxidation state. When Co doping is introduced (x ≤ 0.5), Mn oxidizes from Mn2+ to Mn3+ and Mn4+, while Co largely maintains a valence state of Co2+. In the case of LaCoO3, we identify high-spin and low-spin Co3+ species combined with Co2+. Our investigation underscores the importance to consider the spin and valence states of catalyst materials under operando conditions.

Elucidating the reaction mechanism in heterogeneous catalysis is critically important for catalyst development, yet remains challenging because of the often unclear nature of the active sites. Using a molecularly defined copper single-atom catalyst supported on a UiO-66 metal-organic framework (Cu/UiO-66), allows a detailed mechanistic elucidation of the CO oxidation reaction. Based on a combination of in situ / operando spectroscopies, kinetic measurements including kinetic isotope effects, and density functional theory-based calculations, we identified the active site, reaction intermediates, and transition states of the dominant reaction cycle as well as the changes in oxidation/spin state during reaction. The reaction involves the continuous reactive dissociation of adsorbed O2, by reaction of O2,ad with COad, leading to the formation of an O atom connecting the Cu center with a neighboring Zr4+ ion as rate limiting step. This is removed in a second activated step.

This paper investigates the effect of iron(II) spin state on the catalytic activity of a spin‐crossover (SCO) complex, specifically [Fe(NH2trz)3](NO3)2, in an acetalization reaction. Thanks to its bi‐stability, this complex enables the evaluation of its catalytic activity in both the high‐spin (HS) and low‐spin (LS) states under identical experimental conditions, thereby clearly distinguishing the effects of the spin state from other variables. A notable increase in catalytic efficiency is observed from the low‐spin to the high‐spin state, with the high‐spin complex promoting up to 1.7 times more acetal formation. Extensive experiments across multiple batches of the complex confirm that these findings are both reproducible and representative. To elucidate the underlying mechanism, we assessed the activation energy of the process. The activation energies for both spin states were found to be comparable, suggesting that the observed difference in catalytic activity is not due to electronic factors that stabilize the transition state, but rather to easier access to the catalytic active sites in the high‐spin state. This work represents a significant advancement toward developing a switchable catalytic system based on spin‐crossover phenomena, highlighting that the catalytic activity of SCO complexes can be effectively tuned by the spin state of the metal.

The electronic spin state of metal atomic catalysts is pivotal in determining their catalytic activities. However, such catalysts that are prepared via conventional synthetic approaches often suffer from poorly defined coordination environments, which create challenges in precisely controlling their electronic spin configurations. Herein, we show that a CoFe dual-atom catalyst featuring coordinatively asymmetric FeN2 and CoN3 sites with a fixed coupling distance can be synthesized using a conjugated microporous polymer (designated as CoFe-CMP) and then demonstrate that the catalyst promotes the key reactions underlying both charging and discharge processes of sulfur cathodes. Experimental and theoretical data reveal that the Fe atoms adopt a high-spin state (S = 3/2) and the Co atoms assume a low-spin state (S = 1/2). The former configuration enhances electronic coupling with polysulfides, while the latter promotes the diffusion of Li atoms that are released upon Li2S degradation. Collectively, these processes facilitate the interconversion between polysulfides and Li2S, which are critical for optimizing lithium-sulfur (Li-S) battery operation. Li-S cells containing CoFe-CMP as the sulfur host exhibit outstanding performance in terms of specific capacity (1487 mAh g-1 at 0.1 C), rate capacity (676.3 mAh g-1 at 5 C), and cycling stability (a specific capacity of 499.2 mAh g-1 is measured after 300 cycles at 0.2 C). This research provides a general methodology for tuning the electronic spin states of metal atomic catalysts, as well as guidance for adapting these catalysts for use in other applications.

Co-based catalysts are promising candidates to replace Ir/Ru-based oxides for oxygen evolution reaction (OER) catalysis in an acidic environment. However, both the reaction mechanism and the active species under acidic conditions remain unclear. In this study, by combining surface-sensitive soft X-ray absorption spectroscopy characterization with electrochemical analysis, we discover that the acidic OER activity of Co-based catalysts are determined by their surface oxidation/spin state. Surfaces composed of only high-spin CoII are found to be not active due to their unfavorable water dissociation to form CoIII-OH species. By contrast, the presence of low-spin CoIII is essential, as it promotes surface reconstruction of Co oxides and, hence, OER catalysis. The correlation between OER activity and Co oxidation/spin state signifies a breakthrough in defining the structure-activity relationship of Co-based catalysts for acidic OER, though, interestingly, such a relationship does not hold in alkaline and neutral environments. These findings not only help to design efficient acidic OER catalysts, but also deepen the understanding of the reaction mechanism. Co-based catalysts are promising candidates for oxygen evolution reaction catalysis in an acidic environment, but the structure-activity relationship is unclear. Here, the authors discover that their acidic water oxidation activity is determined by the surface oxidation/spin state.

Precise modulation of the electronic structure in transition metals, particularly the d-band center position and spin state, remains a critical challenge to expediting hydrogen evolution reaction (HER) kinetics. Herein, we report a NiPt/Ni-heterostructured catalyst enabling simultaneous optimization of the d-band electronic structure and spin state of Ni through regulation of the NiPt and Ni bridge sites. Combining operando spectroscopy, X-ray absorption spectroscopy, density functional theory, and ab initio molecular dynamics simulations, we establish that the coordination environment and spin states of Ni at the bridge sites were effectively modulated by altering the Pt content, achieving a transition of Ni centers from the low-spin to high-spin state, and optimized intermediate adsorption/desorption behaviors. The resulting NiPt/Ni catalyst exhibits an exceptional HER performance in acidic media, achieving a benchmark current density of -10 mA cm-2 at a mere 9.8 mV overpotential and delivering an industrial-scale 1.0 A cm-2 current density in PEM electrolysis at 1.75 V.

High‐performance bifunctional electrocatalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is the keystone for the industrialization of rechargeable zinc‐air battery (ZAB). In this work, the modulation in the spin state of Fe single atom on nitrogen doped carbon (Fe1‐NC) is devised by Co3O4 (Co3O4@Fe1‐NC), and a mediate spin state is recorded. Besides, the d band center of Fe is downshifted associated with the increment in eg filling revealing the weakened interaction with OH* moiety, resulting in a boosted ORR performance. The ORR kinetic current density of Co3O4@Fe1‐NC is 2.0‐ and 5.6 times higher than Fe1‐NC and commercial Pt/C, respectively. Moreover, high spin state is found for Co in Co3O4@Fe1‐NC contributing to the accelerated surface reconstruction of Co3O4 witnessed by operando Raman and electrochemical impedance spectroscopies. A robust OER activity with overpotential of 352 mV at 50 mA cm−2 is achieved, decreased by 18 and 60 mV by comparison with Co3O4@NC and IrO2. The operando Raman reveals a balanced adsorption of OH* species and its deprotonation leading to robust stability. The ZAB performance of Co3O4@Fe1‐NC is 193.2 mW cm−2 and maintains for 200 h. Furthermore, the all‐solid‐state ZAB shows a promising battery performance of 163.1 mW cm−2.

Pyrolyzed Fe–N–C materials are cost-effective alternatives to Pt for the acidic oxygen reduction reaction (ORR), yet the atomic and electronic structures of their active centers remain poorly understood. Operando spectroscopic studies have identified potential-induced reversible Fe–N switching in the FeNx active centers of D1 type, which provides a unique opportunity to decode their atomic structures, but the mechanism driving this behavior has been elusive. Herein, using constant-potential ab initio molecular dynamics (CP-AIMD), we reveal that pyridinic FeN4 sites transit reversibly between planar OH*–Fe3+N4 and out-of-plane H2O*–Fe2+N4 configurations at 0.8 V, mirroring the experimental Fe–N switching phenomenon. This shift arises from a spin-state transition: intermediate-spin Fe3+ (S = 3/2) converts to high-spin Fe2+ (S = 2) as potential decreases, driven by the pseudo Jahn–Teller effect and strong H2O binding on the high-spin Fe2+ center. Additionally, a metastable 2H2O*–Fe2.5+N4 configuration exists, acting as a transitional state during the reversible switching process. Calculated X-ray absorption and Mössbauer spectra based on CP-AIMD align closely with experimental data, bridging the theoretical predictions and experimental observations. Crucially, this dynamic Fe–N switching is unique to pyridinic FeN4 sites, challenging the long-held assumption that D1 sites are pyrrolic FeN4. This study clarifies the potential-driven dynamics and active center structures in Fe–N–C catalysts and will help to precisely design Fe-based ORR catalysts.

The emerging electrocatalytic C-N coupling reaction provides an attractive route toward green urea synthesis, but a lack of in-depth insight into the catalytic mechanism and the geometric/electronic configurations that determine the key C- and N-coupling intermediates formation hampers the exploration of efficient catalysts. Herein, we design a bimetallic oxide (Fe-Mo-O) with dual active sites of Fe and Mo for the adsorption and activation of NO2- and CO2, respectively. Constructing dual-metal catalyst leads to an upshift of the d-band center and the generation of an intermediate-spin Fe center, which not only favors the selective conversion of *CO2 into the key intermediate *CO on Mo sites, but also facilitates the adsorption and reduction of NO2- on Fe sites. Operando characterizations and theoretical calculations together elucidate that urea generation is associated with the formation of *CONH2 intermediate by coupling *CO and *NH2 on the alternating Mo and intermediate-spin Fe active sites, ultimately synergistically lowering the C-N coupling energy barrier. Specifically, the Fe-Mo-O catalyst delivers a high urea yield rate of 681.8 μg h-1 mg-1cat. and an excellent Faradaic efficiency of 60% at -0.5 V (vs. RHE). Furthermore, a C-N coupling paired with a glycerol oxidation system allows for energy-saving electrochemical coproduction of urea and formic acid. Our findings offer a feasible strategy to develop cutting-edge electrocatalysts for urea synthesis by active site design and electronic structure regulation.

Precisely tailoring the electronic structure of the single-atom center is significant to improve the intrinsic reactivity of single-atom catalysts and elucidate the underlying reaction mechanism, but this remains highly challenging. Herein, we construct covalently oxygen-bridged single-Fe-atom sites on carbon nanotubes, dominated by low-spin (LS) Fe(III) sites, as an efficient catalyst for boosting the intrinsic catalytic performance for the electrochemical CO2 reduction reaction (CO2RR). A maximal CO Faradaic efficiency of 99% with an extremely high turnover frequency of 5.3 × 104 h-1 at an applied cathodic potential of -0.7 V vs RHE is achieved, showing a more than 20-fold increase as compared to that of high-spin (HS) Fe(III) sites. Taking advantage of operando and rapid freeze-quenched 57Fe Mössbauer spectroscopy, together with operando X-ray absorption spectroscopy, a spin-driven CO2 electroreduction mechanism is identified, wherein the in-situ-generated HS Fe(II) and LS Fe(II) sites dominate the CO2RR at the low and high overpotentials, respectively. Furthermore, results from operando Raman and attenuated total reflectance surface-enhanced infrared absorption spectroscopy reveal that the one-electron reduction of phthalocyanine (Pc) coordinated to the central Fe leads to a weaker bonding strength of *CO on the LS O-Fe(II)Pc- sites. Density functional theory calculations further illustrate the increased Bader charge and d-band center of the in-situ-generated LS O-Fe(II)Pc-, facilitating the delocalization of electrons from the Fe 3d orbital to the 2pz orbital of CO2, thus reducing the formation free energy of the *COOH intermediate and boosting the CO2RR performance.

High‐entropy materials offer unique advantages in catalysis due to lattice distortion, compositional complexity, and entropy‐driven stability. In this study, we report a crystal phase‐engineered high‐entropy perovskite oxide, LaB5O3 (B═Fe, Cu, Co, Cr, and Ni), which enables efficient bifunctional electrocatalysis. Structural transformation from orthorhombic to cubic symmetry modulates the spin states of B‐site metals, particularly stabilizing the high‐spin state of Fe2⁺/Fe3⁺, enhancing electron density and nitrate adsorption. This leads to a NH3 Faradaic efficiency (FE) of 95.83% at −0.7 V vs. RHE for nitrate reduction (NO3RR), with minimal NO2;− byproduct (FE < 2%). Concurrently, LaB5O3 exhibits excellent sulfide oxidation reaction (SOR) activity, requiring only 0.484 V vs. RHE at 10 mA cm−2—considerably lower than oxygen evolution reaction (OER) overpotential. Integrated into a paired electrolyzer, the system achieves simultaneous nitrate‐to‐ammonia conversion (max FE: 81.27%) and sulfide‐to‐sulfur transformation at a cell voltage of just 1.079 V. The superior performance arises from synergistic effects of high‐entropy design, including enhanced oxygen vacancy formation, lattice strain, and ferroelectricity. This work demonstrates the potential of crystal phase engineering in high‐entropy oxides for sustainable nitrogen fixation and sulfur recovery in water treatment applications.

The oxygen evolution reaction (OER) involves the recombination of diamagnetic hydroxyl (OH) or water (H2O) into the paramagnetic triplet state of oxygen (O2). The spin conservation of oxygen intermediates plays a crucial role in OER, however, research on spin dynamics during the catalytic process remains in its early stages. Herein, β‐Ni(OH)2 and Fe‐doped β‐Ni(OH)2 (Ni5Fe1(OH)2) are utilized as model catalysts to understand the mechanism of spin magnetic effects at iron (III) sites during OER. Combined with magnetic characterization, it is founded that the introduction of Fe transforms the antiferromagnetic Ni(OH)2 into a ferromagnetic material. Testing the magnetic response of the catalyst under an external magnetic field, the OER activity of Ni5Fe1(OH)2 is significantly enhanced in comparison to Ni(OH)2. This improvement is likely due to the introduction of iron sites, which promote spin magnetic effects and enhance reaction kinetics, thereby increasing catalytic efficiency. Combining experimental and theoretical characterization, it is discovered that the iron sites accelerate the formation of heterogeneous dual‐site O─O bridging, represented as ─Ni─O─O─Fe─, thereby effectively enhancing the kinetics of the OER reaction. This study provides a magnetic perspective on the structure‐function relationship of magnetic iron‐based catalysts and has significant implications for the design of new catalysts.

Though there are many synthetic iron-sulfur clusters that have been reported to show catalytic activity mimicking the natural cofactors in metalloenzymes, the influence of the spin state on the catalytic property is seldom touched. Here, a disulfide-bridged triiron(II) complex is shown, namely [Fe3(Sip)4][CF3SO3]2 (Fe3(Sip)4, HSip = sulfanylpropyliminomethyl-pyridine), can efficiently electrocatalyze water oxidation with a turnover frequency of 932 s-1 and Faraday efficiency of 86%, better than many iron-based catalysts. More importantly, the terminal low-spin (S = 0) iron(II) sites possessing a N4S2 first coordination environment, along with the synergetic catalysis of ligands, play a crucial role in the catalytic process. This research highlights the unconventional applications of iron-sulfur clusters in electrocatalytic water oxidation and underlines a promising avenue for developing innovative catalysts.

Abstract The industrially important Cu/ZnO:Al (CZA) catalyst is known as a dynamic system adapting to reaction conditions, which renders the application of in situ and operando methods key to establish structure function correlations. Herein, a CZA catalyst close to the industrially used compostion was studied using noninvasive and bulk‐sensitive in situ/operando microwave cavity perturbation technique and electron paramagnetic resonance spectroscopy during activation and reverse water gas shift reaction. The transient changes of catalytic activity track with the transients of the dielectric properties providing evidence for the importance of bulk properties for catalytic activity. Furthermore, convincing support for the redox reaction mechanism is obtained, and it is shown that H2 and CO2 uptake is not competing kinetically with each other. In addition, the reservoir of H2 and CO2 transiently present in the catalyst during catalysis is determined by the chemical potential of the respective reactant, which is directly coupled to the catalytic activity of the system. The findings fit the model of a Schottky barrier at the Cu/ZnO:Al interface, altered by the gas phase composition which in turn alters the catalytic properties of the system.

Cost-effective redox-active materials are essential for advancing redox flow batteries (RFBs). Iron, with its abundance and suitability as a redox couple, is a promising candidate; however, achieving stable and fast redox reactions in aqueous RFBs remains a challenge. This study presents an Fe-based negolyte stabilized by a hexadentate ligand, where Fe-ligand bonds are enhanced through intermolecular interactions. The sulfonate-substituted Fe complex exhibits a formal potential of -0.44 V vs. Ag/AgCl and an exceptionally high rate constant of 0.69 cm s-1. Near-neutral RFBs incorporating 0.5 M Fe complex show excellent cycling stability, with no discernable capacity fading over 300 cycles. This performance is attributed to intermolecular hydrogen bonds that reinforce Fe-ligand coordination and promote the formation of stable trimeric clusters. Operando electrochemical Raman spectroscopy and density functional theory reveal that π-backdonation from Fe(II) to the imino-phenolate moiety further stabilizes the complex after reduction. In contrast, the hydroxyl-substituted complex exhibits inferior stability due to weaker hydrogen bonding and less pronounced π-backdonation. These findings underscore the importance of ligand design and intermolecular interactions in developing cost-effective, high-performance redox-active materials for aqueous RFBs.

Co(iii) complexes are increasingly prevalent in homogeneous catalysis. Catalytic cycles involve multiple intermediates, many of which will feature unsaturated metal centres. This raises the possibility of multi-state character along reaction pathways and so requires an accurate approach to calculating spin-state energetics. Here we report an assessment of the performance of DLPNO-CCSD(T) (domain-based local pair natural orbital approximation to coupled cluster theory) against experimental 1Co to 3Co spin splitting energies for a series of pseudo-octahedral Co(iii) complexes. The alternative NEVPT2 (strongly-contracted n-electron valence perturbation theory) and a range of density functionals are also assessed. DLPNO-CCSD(T) is identified as a highly promising method, with mean absolute deviations (MADs) as small as 1.3 kcal mol-1 when Kohn-Sham reference orbitals are used. DLPNO-CCSD(T) out-performs NEVPT2 for which a MAD of 3.5 kcal mol-1 can be achieved when a (10,12) active space is employed. Of the nine DFT methods investigated TPSS is the leading functional, with a MAD of 1.9 kcal mol-1. Our results show how DLPNO-CCSD(T) can provide accurate spin state energetics for Co(iii) species in particular and first row transition metal systems in general. DLPNO-CCSD(T) is therefore a promising method for applications in the burgeoning field of homogeneous catalysis based on Co(iii) species.

No abstract available

Significance Although Fenton-like reactions utilizing H2O2 gained widespread application, enhancing the reaction activity under neutral or alkaline conditions remained a challenge. During the process of Fenton-like activation, alterations in the spin state of active sites could significantly impact electron transfer and modulate the formation of active intermediates, thereby influencing reaction activity across different pH conditions. We proposed a strategy that optimizes the spin interaction between Fe sites and coordination O atoms, thereby refining the H2O2 activation pathway with O2•−as the primary active species. This approach demonstrated exceptional efficiency, stability, and pH tolerance for pollutant removal. Consequently, it presented an appealing avenue for regulating selective free radical generation during H2O2 activation and advancing neutral organic wastewater treatment.

Iron‐based single‐atom catalysts (Fe─N─C) exhibit excellent oxygen reduction activity but struggle with bifunctional performance due to their poor oxygen evolution activity. Although the Fe spin state is found to be closely associated with enhanced bifunctional activity, controllably regulating the Fe spin state remains a challenge. Here, the controllable regulation of Fe spin state is directly achieved through competitive coordination between chlorine and pyridine nitrogen in the axial direction of Fe─N4. The spin state of Fe is regulated from high spin to intermediate spin by the modulation of axial ligands from weak‐field ligand chlorine to strong‐field ligand pyridinic nitrogen, which leads to the enhanced bifunctional activity of N─FeN4 with a small potential gap (ΔE = 0.68 V). Theoretical calculations indicate that the spin state turning is accompanied by an enhanced binding strength between Fe sites and *OH leading to a significant decrease in the OER barrier. Moreover, N─FeN4 exhibits sufficient durability for oxygen reduction reaction (ORR) (over 50 h), oxygen evolution reaction (OER) (over 200 h), and the assembled zinc–air battery (over 1000 h). Here a novel approach is proposed for designing efficient catalysts based on spin state and profound insights into Fe─N─C spin state for bifunctional oxygen catalysis.

Although the catalytic activity is heavily reliant on the electronic structure of the catalyst, understanding the impact of electron spin regulation on electrocatalytic performance is still rarely investigated. This work presents a novel approach involving the single-atom coordination of cobalt (Co) within metalloporphyrin-based three-dimensional covalent organic frameworks (3D-COFs) to facilitate the catalytic conversion for sodium-iodine batteries. The spin state of Co is modulated by altering the oxidation state of the porphyrin-centered Co, achieving optimal catalysis for iodine reduction. Experimental results demonstrate that CoII and CoIII are incorporated into the 3D-COFs, exhibiting spin ground states of S = 1/2 and S = 0, respectively. The low spin state of CoIII is favorable to hybridize with the sp 3d orbitals of I3-, thus facilitating the conversion of I3- to I-. Density-functional theory (DFT) calculations further reveal that the presence of CoIII enhances iodide adsorption and accelerates the formation of NaI in 3D-COFs-CoIII, thereby promoting its rapid kinetic behaviors. Notably, the I2@3D-COFs-CoIII cathode achieves a high reversible capacity of 227.7 mAh g-1 after 200 cycles at 0.5 C and demonstrates exceptional cyclic stability, exceeding 2000 cycles at 10 C with a minor capacity fading rate of less than one 0.01% per cycle.

Spin catalysis offers a new perspective for developing highly efficient catalytic reactions by leveraging electron angular momentum—another fundamental parameter controlling the chemical reaction. Electron spin plays a critical role in reactions including but not limited to electrochemistry, photochemistry, and organic synthesis. However, the correlation between spin state and reaction efficiency remains incompletely elucidated, which hinders the advancement in this field. The unique capabilities of single‐molecule platforms enable real‐time spin‐state observation and precise manipulation, thus inspiring the exploration of their potential to advance spin catalysis. Accordingly, this perspective examines the prospects of single‐molecule platforms in spin catalysis, with the goal of fostering interdisciplinary research to elucidate the mechanism of spin catalysis and develop novel synthesis methodologies based on precise control of spin states. We first discuss the influence of electron spin on spin‐dependent reaction thermodynamics and kinetics, along with effective approaches to achieve spin manipulation. Building on this foundation, we summarize key challenges and opportunities in spin catalysis and evaluate the potential of single‐molecule platforms for mechanistic studies and precision synthesis in spin catalysis, including efficient spin injection, precise spin‐state detection, and coherent spin manipulation.

No abstract available

Photoswitchable catalysis provides a non‐invasive strategy for dynamically controlling light‐driven chemical energy conversion processes. The defining advantage of photoswitchable catalytic systems lies in their unique dual capacity: i) spatiotemporal precision in resolving reactive species generation through optical addressing; and ii) adaptive multifunctionality enabling on‐demand switching between distinct active phases, thereby suppressing competing pathways and eliminating undesired side reactions. Current research paradigms remain predominantly anchored in molecular systems, whereas solid‐state semiconductor architectures—with their inherent advantages in recyclability and thermal stability—suffer from critical deficiencies in excitation‐selective reactivity modulation and interfacial charge transfer kinetics. Here we comment on a recent work, writing in National Science Review, reported spin–orbit coupling‐mediated control over anti‐Kasha photophysical pathways in semiconductors of carbonylated carbon nitride, enabling optically switchable catalytic dynamics. We further analyzed the profound implications of this work and presented a forward‐looking outlook on the future development of the photoswitchable catalysis.

Alloying has significantly upgraded the oxygen reduction reaction (ORR) of Pd‐based catalysts through regulating the thermodynamics of oxygenated intermediates. However, the unsatisfactory activation ability of Pd‐based alloys toward O2 molecules limits further improvement of ORR kinetics. Herein, the precise synthesis of nanosheet assemblies of spin‐polarized PdCu–Fe3O4 in‐plane heterostructures for drastically activating O2 molecules and boosting ORR kinetics is reported. It is demonstrated that the deliberate‐engineered in‐plane heterostructures not only tailor the d‐band center of Pd sites with weakened adsorption of oxygenated intermediates but also endow electrophilic Fe sites with strong ability to activate O2 molecules, which make PdCu–Fe3O4 in‐plane heterostructures exhibit the highest ORR specific activity among the state‐of‐art Pd‐based catalysts so far. In situ electrochemical spectroscopy and theoretical investigations reveal a tandem catalytic mechanism on PdCu–Fe3O4─Fe sites that initially activate molecular O2 and generate oxygenated intermediates being transferred to Pd sites to finish the subsequent proton‐coupled electron transfer steps.

Lithium-sulfur (Li-S) batteries suffer from sluggish kinetics due to the poor conductivity of sulfur cathodes and polysulfide shutting. Current studies on sulfur redox catalysis mainly focus on the adsorption and catalytic conversion of lithium polysulfides but ignore the modulation of the electronic structure of the catalysts which involves spin-related charge transfer and orbital interactions. In this work, bimetallic phosphorus trisulfides embedded in Prussian blue analogue-derived nitrogen-doped hollow carbon nanocubes (FeCoPS3/NCs) were elaborately synthesized as a host to reveal the relationship between the catalytic activity and the spin state configuration for Li-S batteries. Orbital spin splitting in FeCoPS3 drives the electronic structure transition from low-spin to high-spin states, generating more unpaired electrons on the 3d orbit. Specifically, the nondegenerate orbitals involved in the high-spin configuration of FeCoPS3 result in the upshift of energy levels, generating more active electronic states. Such tailored electronic structure increases the charge transfer, influences the d-band center, and further modifies the adsorption energy with lithium polysulfides and the potential reaction pathways. Consequently, the cell with FeCoPS3/NC host exhibits an ultralow capacity decay of 0.037% per cycle over 1000 cycles. This study proposed a general strategy for sculpting geometric configurations to enable spin and orbital topology regulation in Li-S battery catalysts.

Two‐electron oxygen reduction reaction (2e − ORR) offers a sustainable approach to traditional hydrogen peroxide (H 2 O 2 ) production, and can be scaled up in production capacity and efficiency through integrated energy conversion devices. Achieving the electrosynthesis of H 2 O 2 at low electrolytic cell voltages not only reduces energy consumption but also improves economic efficiency. Herein, we engineered the Ga sites as potential‐dependent spin‐state promoters at interatomic distances into highly active single‐atom Co sites. In this system, electron‐rich Ga atoms donate extra anti‐bonding orbital electrons to Co to induce an in situ transition of Co from a medium‐spin (0.70 V) to a low‐spin configuration (0.20 V), thereby facilitating smoother intermediates release. In parallel, Ga improves local hydrophilicity and surface polarity toward accelerated proton transfer. Impressively, the catalyst retains >90% H 2 O 2 selectivity even if the reaction enters the low‐voltage stage and enables a production rate of 13.7 mol g cat −1 h −1 in a flow cell.

The single-atom Fe-N-C catalyst has shown great promise for the oxygen reduction reaction (ORR), yet the intrinsic activity is not satisfactory. There is a pressing need to gain a deeper understanding of the charge configuration of the Fe-N-C catalyst and to develop rational modulation strategies. Herein, we have prepared a single-atom Fe catalyst with the co-coordination of N and O (denoted as Fe-N/O-C) and adjacent defect, proposing a strategy to optimize the d-orbital spin-electron filling of Fe sites by fine-tuning the first coordination shell. The Fe-N/O-C exhibits significantly better ORR activity compared to its Fe-N-C counterpart and commercial Pt/C, with a much more positive half-wave potential (0.927 V) and higher kinetic current density. Moreover, using the Fe-N/O-C catalyst, the Zn-air battery and proton exchange membrane fuel cell achieve peak power densities of up to 490 and 1179 mW cm-2, respectively. Theoretical studies and in situ electrochemical Raman spectroscopy reveal that Fe-N/O-C undergoes charge redistribution and negative shifting of the d-band center compared to Fe-N-C, thus optimizing the adsorption free energy of ORR intermediates. This work demonstrates the feasibility of introducing an asymmetric first coordination shell for single-atom catalysts and provides a new optimization direction for their practical application.

The selectivity of multicarbon products in the CO2 reduction reaction (CO2RR) depends on the spin alignment of neighboring active sites, which requires a spin catalyst that facilitates electron transfer with antiparallel spins for enhanced C-C coupling. Here, we design a radical-contained spin catalyst (TEMPOL@HKUST-1) to enhance CO2-to-ethylene conversion, in which spin-disordered (SDO) and spin-ordered (SO) phases co-exist to construct an asymmetric spin configuration of neighboring active sites. The replacement of axially coordinated H2O molecules with TEMPOL radicals introduces spin-spin interactions among the Cu(II) centers to form localized SO phases within the original H2O-mediated SDO phases. Therefore, TEMPOL@HKUST-1 derived catalyst exhibited an approximately two-fold enhancement in ethylene selectivity during the CO2RR at -1.8 V versus Ag/AgCl compared to pristine HKUST-1. In situ ATR-SEIRAS spectra indicate that the spin configuration at asymmetric SO/SDO sites significantly reduces the kinetic barrier for *CO intermediate dimerization toward the ethylene product. The performance of the spin catalyst is further improved by spin alignment under a magnetic field, resulting in a maximum ethylene selectivity of more than 50%. The exploration of the spin-polarized kinetics of the CO2RR provides a promising path for the development of novel spin electrocatalysts with superior performance.

The selective hydrogenation of NO to NH2OH governs the performance of cyclohexanone oxime electrosynthesis. However, the spin state transition during the NO-to-NH2OH process, which is directly related to reaction pathways, has long been ignored. Here, we propose a spin locking mechanism via density functional theory and sure independence screening and sparsifying operator. Magnetic sites with medium spin states stabilize the *NHO intermediate by locking the spin configuration of NO to weaken *NH2OH adsorption for high selectivity. The spin magnetic moment (µS), the angle between *N-O and the catalyst (θ), and the charge state (q) are key factors, providing a screening range of the predictive metrics (µS·θ)3 and (cos θ/q). The theoretically selected NiFe2O4 delivers 70% Faradaic efficiency for cyclohexanone oxime, and weakened *NH2OH adsorption is revealed by in situ spectroscopy. This work highlights the importance of spin regulation in adjusting the selectivity of electrosynthesis.

Molecular oxygen activation at single transition metal atom sites is critical for catalysis but remains challenging to control. Here we investigate a manganese-cobalt bi-metallic coordination network on graphene, where Co(I) atoms are tetracoordinated by nitrogen. Combining density functional theory with in situ infrared-visible sum-frequency generation and ambient-pressure X-ray photoelectron spectroscopy, we demonstrate pressure-dependent oxygen ligation at Co sites. Below 10-6 mbar, O2 binds reversibly in a horizontal configuration, inducing charge transfer and a triplet-to-singlet spin transition characteristic of an active superoxo O2δ- species. Increasing oxygen pressure leads to O2 dissociation, with atomic oxygen accumulating at Co(II) sites and at the support. Co-exposure to O2 and CO enables room-temperature oxidation of the latter, preventing catalyst poisoning. These findings reveal how coordination and environmental control tune spin, oxidation state, and reactivity at single metal atoms, offering pathways for rational design of atomically precise two-dimensional catalysts.

Spin manipulation of transition-metal catalysts has great potential in mimicking enzyme electronic structures to improve catalytic activity and product selectivity. However, it remains a great challenge to manipulate spin state of catalytic centers for their fixed electronic configurations at room temperature. Herein, we report a facile mechanical exfoliation strategy to in-situ induce partial spin crossover from high-spin (s = 5/2) to low-spin (s = 1/2) of the ferric center across the lattice. Due to spin transition of catalytic center, mixed-spin catalyst exhibits a high CO yield of 19.7 mmol g-1 with selectivity of 91.6%, much superior to that of high-spin bulk counterpart (50% selectivity). Density functional theory calculations reveal that low-spin 3d-orbital electronic configuration performs a key function in increasing orbital overlap, significantly promoting CO2 selective adsorption and reducing its activation barrier. Hence, the facile spin manipulation through mechanical exfoliation highlights a new insight into designing highly efficient biomimetic catalysts via optimizing spin state.

The electrocatalytic nitrogen oxidation reaction (eNOR) offers a sustainable route for nitrate (NO 3 ‒ ) synthesis, yet its practical application is limited by sluggish intermediate formation kinetics. Although •OH generated during water oxidation can promote the formation of the key * NOH intermediate, the cooperative mechanism between •OH and catalytic sites remains insufficiently understood. Herein, a spin‐state modulation strategy is proposed to enhance * NOH generation under simulated solar irradiation, thereby markedly improving the NO 3 ‒ yield and Faradaic efficiency (FE) of the eNOR. A heterojunction catalyst consisting of CoMo‐based layered double hydroxide nanosheets grown in situ on Ti 3 C 2 T x MXene (CoMo‐LDH@Ti 3 C 2 T x ) was developed to enable light‐assisted eNOR. The incorporation of Mo into Co‐LDH, together with the built‐in electric field of the heterojunction, enhances Mo–Co orbital hybridization and induces a spin‐state transition of Co 3+ centers from t 2g 6 e g 0 to t 2g 4 e g 2 configuration. This electronic regulation strengthens N 2 activation and accelerates * NOH formation via the cooperative involvement of two •OH radicals under illumination, thereby significantly boosting eNOR kinetics. Consequently, CoMo‐LDH@Ti 3 C 2 T x delivers NO 3 ‒ yield of 198.55 µg h −1 mg cat. −1 and FE of 46.22% under solar light, outperforming dark conditions and state‐of‐the‐art catalysts. These findings underscore the critical roles of spin‐state engineering and radical synergy in advancing sustainable nitrate production.

Manipulating the spin ordering of the oxygen evolution reaction (OER) catalysts through magnetization has recently emerged as a promising strategy to enhance performance. Despite numerous experiments elaborating on the spin magnetic effect for improved OER, the origin of this phenomenon remains largely unexplored, primarily due to the difficulty in directly distinguishing the spin states of electrocatalysts during chemical reactions at the atomic level. X-ray emission spectroscopy (XES), which provides information sensitive to the spin states of specific elements in a complex, may serve as a promising technique to differentiate the onset of OER catalytic activities from the influence of spin states. In this work, we employ the in situ XES technique, along with X-ray absorption spectroscopy (XAS), to investigate the interplay between atomic/electronic structures, spin states, and OER catalytic activities of the CoFe2O4 (CFO) catalyst under an external magnetic field. This enhancement is due to the spin magnetic effect that facilitates spin-selective electron transfer from adsorbed OH– reactants, which strongly depends on the spin configurations of the tetrahedral-(Td) and octahedral-(Oh) sites of both Fe and Co ions. Our result contributes to a comprehensive understanding of magnetic field-assisted electrocatalysis at the atomic level and paves the way for designing highly efficient OER catalysts.

ABSTRACT Fe-N-C catalysts have emerged as a promising substitute for the expensive Pt/C to boost the oxygen reduction reaction (ORR). However, conventional Fe-N4 active sites, which generally feature a low-spin configuration, strongly adsorb oxygen intermediates and necessitate structural optimization of the active sites for improved performance. Herein, graphitic nitrogen (NGC) adjacent to the Fe-N4 centers is straightforwardly introduced to modulate the spin state of Fe-N-C catalysts after elucidating the influence of nitrogen species on the Fe-N4 sites. Theoretical calculations demonstrate that the adjacent NGC can effectively regulate the spin state of the active Fe sites, which enables electron filling from Fe to the anti-bonding π* orbital of oxygen species and optimizes the *OH desorption for accelerated ORR. Inspired by this, such catalysts are cost-effectively prepared by a rational combination of electrospinning and controlled thermal annealing using inexpensive precursors. The optimal catalyst shows superior ORR activity to the benchmark Pt/C, and excellent durability, with a minor voltage decay of 11 mV after 10 000 cycles. The spin-state-promoted performance enhancement is confirmed by a series of in-situ characterizations. The remarkable performance of the optimized catalyst is further confirmed in Zn-air batteries (ZABs) with a peak power density of 225 mW cm−2. Moreover, quasi-solid ZABs using this catalyst realize excellent performance even under bending conditions and successfully power electronic devices, including a mobile phone and an electronic watch. This work correlates the spin state of catalysts and oxygen reduction performance, providing an alternative strategy for regulating the performance of electrocatalysts as well as promoting their application in wearable electronics.

In situ studies of the relationship between surface spin configurations and spin-related electrocatalytic reactions are crucial for understanding how magnetic catalysts enhance oxygen evolution reaction (OER) performance under magnetic fields. In this work, 2D Fe7Se8 nanosheets with rich surface spin configurations are synthesized via chemical vapor deposition. In situ magnetic force microscopy and Raman spectroscopy reveal that a 200 mT magnetic field eliminates spin-disordered domain walls, forming a spin-ordered single-domain structure, which lowers the OER energy barrier, as confirmed by theoretical calculations. Electrochemical tests show that under a 200 mT magnetic field, the OER overpotential of multidomain Fe7Se8 nanosheets at 10 mA cm-2 decreases from 346 mV to 259 mV, while the magnetic field has minimal effect on single-domain nanosheets. These findings highlight the critical role of spin configurations in enhancing electrocatalytic performance, offering new insights into the design of magnetic catalysts for industrial applications.

Although high-valent metal hydroxyl oxides formed in situ through electrochemical oxidation of the metal oxide matrix are key active sites for the oxygen evolution reaction (OER) in transition metal oxides, such a sluggish structural reconstruction largely hinders the electrocatalytic performance. Herein, we present a novel spin polarization engineering strategy to accelerate the formation of high-valent CoOOH, thereby significantly enhancing the OER performance. Through strategic substitutional doping of Mn atoms into the CoO lattice and subsequent confinement of the resulting bimetallic oxides within hollow mesoporous carbon spheres (Mn–CoO/HMCS), the as-prepared catalyst demonstrates markedly enhanced electrocatalytic activity, delivering approximately 5.9-fold higher mass activity compared to the undoped CoO/HMCS counterpart. In situ spectroscopy and theoretical calculations elucidate that Mn doping induces lattice distortion and symmetry breaking, which alters the orbital filling of Co with a lower energy barrier for the structural reconstruction from Co2+ to Co3+. The spin state transition from a high-spin configuration in Co2+ to a low-spin state in Co3+ further facilitates the formation of CoOOH active intermediates for OER. This work not only paves new avenues for promoting the dynamic reconstruction of active hydroxyl oxides but also highlights the untapped potential of cobalt-based materials through rational electronic structure modulation.

Single-atom catalysts (SACs) with M–N4 active sites show great potential to catalyze the electrochemical CO2 reduction reaction (eCO2RR) toward CO. The activity and selectivity of SACs are determined by the local coordination configuration of central metal atoms in M–N4 sites, which is readily tuned by axial ligands. In this work, we construct axial ligands in situ on two Ni–N4-type model SACs, NiPc and Ni–N–C, by adding Cl− into the electrolyte taking advantage of the strong chemisorption of Cl− over Ni–N4. Cl axial ligand lowers the energy barrier of the potential-determining step for the eCO2RR due to a hybridization state transition of Ni orbitals and the resulting rearrangement of spin electrons. Consequently, both NiPc and Ni–N–C with axial Cl exhibit superior activity for the eCO2RR toward CO. Finally, we propose the magnetic moment of Ni as a universal descriptor for the eCO2RR toward CO on Ni–N4 with various axial ligands.

Catalytic conversion of lithium polysulfides (LiPSs) is a crucial approach to enhance the redox kinetics and suppress the shuttle effect in lithium–sulfur (Li–S) batteries. However, the roles of a typical heterogenous catalyst cannot be easily identified due to its structural complexity. Compared with the distinct sites of single atom catalysts (SACs), each active site of single site catalysts (SSCs) is identical and uniform in their spatial energy, binding mode, and coordination sphere, etc. Benefiting from the well‐defined structure, iron phthalocyanine (FePc) is covalently clicked onto CuO nanosheet to prepare low spin‐state Fe SSCs as the model catalyst for Li–S electrochemistry. The periodic polarizability evolution of Fe‐N bonding is probed during sulfur redox reaction by in situ Raman spectra. Theoretical analysis shows the decreased d‐band center gap of Fe (Δd) and delocalization of dxz/dyz after the axial click confinement. Consequently, Li–S batteries with Fe SSCs exhibit a capacity decay rate of 0.029% per cycle at 2 C. The universality of this methodological approach is demonstrated by a series of M SSCs (M = Mn, Co, and Ni) with similar variation of electronic configuration. This work provides guidance for the design of efficient electrocatalysis in Li–S batteries.

Against the backdrop of escalating global energy crises and environmental challenges, the development of clean and sustainable hydrogen energy has become increasingly imperative. Hydrogen production via water electrolysis is widely regarded as a promising approach due to its green and efficient characteristics. In this study, we propose an antiperovskite nitride catalyst (CuNNi 3‐ x Fe x ) to enhance its electrocatalytic performance. Specifically, electronic structure modulation was achieved through Fe doping at partial Ni sites, which effectively alters the 3d orbital electron configuration of Ni. Such electronic optimization facilitates more favorable adsorption of reaction intermediates and significantly improves electrocatalytic performance. The optimized CuNNi 2.25 Fe 0.75 catalyst exhibits markedly enhanced activity, delivering 10 mA cm −2 at overpotentials of only 63 mV for hydrogen evolution reaction (HER) and 254 mV for oxygen evolution reaction (OER). Furthermore, for overall water splitting, the catalyst requires a low cell voltage of 1.52 V to achieve the same current density. In situ Raman confirms that the change in spin state facilitates the formation of NiOOH during OER. DFT calculations reveal that Fe doping reduces reaction energy barriers and accelerates kinetics via electronic structure modulation, thereby substantially enhancing the electrocatalytic efficiency.

The spin states of active sites have a significant impact on the adsorption/desorption ability of the reaction intermediates during the oxygen evolution reaction (OER). Sulfide spinel is not generally considered a highly efficient OER catalyst owing to the low spin state of Co3+ and the lack of unpaired electrons available for adsorption of reaction intermediates. Herein, it is proposed a novel Nd‐evoked valence electronic adjustment strategy to engineer the spin state of Co ions. The unique f‐p‐d orbital electronic coupling effect stimulates the rearrangement of Co d orbital electrons and increases the eg electron filling to achieve high‐spin state Co ions, which promotes charge transport by propagating a spin channel and generates a high number of active sites for intermediate adsorption. The optimized CuCo1.75Nd0.25S4 catalyst exhibits outstanding electrocatalytic properties with a low overpotential of 320 mV at 500 mA cm−2 and a 48 h stability at 300 mA cm−2. In situ synchrotron radiation infrared spectra confirm the quick accumulation of key *OOH and *O intermediates. This work deepens the comprehensive understanding of the relationship between OER activity and spin configurations of Co ions and offers a new design strategy for spinel compound catalysts.

Fe-based catalysts have garnered considerable attention for NO3⁻ removal and conversion. However, antagonistic NO3⁻/PO43⁻ removal, low N2 selectivity, and slow degradation kinetics limit the application of Fe-based hydroxide catalysts in green denitration. In this study, an innovative La-mediated green rust (La-GR) bimetallic hydroxide was designed and synthesized, achieving over 80 % synchronous and targeted removal of NO3⁻ and PO43⁻. Combined transient reaction analyses and DFT calculations revealed that La-O-Fe coordination reconstructs the electronic structure at the catalytic interface, decoupling reduction and adsorption processes to replace competitive antagonism with synergistic promotion, thereby enabling simultaneous nitrogen and phosphorus removal. The in-situ formation of LaPO4 enhanced the built-in electric field of La-GR, creating a microenvironment conducive to local NO3⁻ reduction. The La/Fe exchange process synergistically modulated magnetic exchange interactions within GR by elevating the d-band center and reducing the spin state of the Fe sites. This optimized d-orbital electron configuration lowered the adsorption energy of nitrogen at the Fe sites and facilitated N2 desorption, thereby achieving precise regulation of N2 selectivity up to 88.83 %. Overall, this coupling of functional differentiation and spin regulation offers new paradigms for designing high-performance catalysts and elucidating catalytic mechanisms at the spin-electron scale.

No abstract available

Room‐temperature sodium–sulfur (RT Na–S) batteries are promising candidates for large‐scale energy storage owing to their high energy density and low cost, yet their practical deployment is hindered by sluggish sulfur redox kinetics and severe polysulfide shuttling. Here, guided by density functional theory (DFT) calculations, we develop a class of axially oxygen‐coordinated ferromagnetic single‐atom catalysts (SACs) with enhanced spin polarization to accelerate sulfur conversion. Among Fe‐, Co‐, and Ni‐based SACs, Co–N2O3 is theoretically identified as the most effective configuration, featuring an optimized electronic structure with a minimal energy offset (0.26 eV) between the Co d‐band and S p‐band centers, which facilitates Na+ diffusion and lowers the activation barrier for polysulfide conversion. Experimentally, Co–N2O3 atoms anchored on hollow mesoporous carbon spheres (Co–N2O3@MCS) exhibit outstanding catalytic activity as the sulfur host, achieving an ultrahigh rate capability (330.5 mAh g−1 at 10 A g−1) and excellent durability over 600 cycles at 1 A g−1. In situ characterizations reveal that the enhanced ferromagnetism effectively suppresses polysulfide shuttling, underscoring the crucial role of coordination‐engineered spin polarization in boosting the redox kinetics of RT Na–S batteries.

High-valent metal-oxo moieties have been implicated as key intermediates preceding various oxidation processes. The critical O–O bond formation step in the Kok cycle that is presumed to generate molecular oxygen occurs through the high-valent Mn-oxo species of the water oxidation complex, i.e., the Mn4Ca cluster in photosystem II. Here, we report the spectroscopic characterization of new intermediates during the water oxidation reaction of manganese-based heterogeneous catalysts and assign them as low-spin Mn(IV)-oxo species. Recently, the effects of the spin state in transition metal catalysts on catalytic reactivity have been intensely studied; however, no detailed characterization of a low-spin Mn(IV)-oxo intermediate species currently exists. We demonstrate that a low-spin configuration of Mn(IV), S = 1/2, is stably present in a heterogeneous electrocatalyst of Ni-doped monodisperse 10-nm Mn3O4 nanoparticles via oxo-ligand field engineering. An unprecedented signal (g = 1.83) is found to evolve in the electron paramagnetic resonance spectrum during the stepwise transition from the Jahn–Teller-distorted Mn(III). In-situ Raman analysis directly provides the evidence for Mn(IV)-oxo species as the active intermediate species. Computational analysis confirmed that the substituted nickel species induces the formation of a z-axis-compressed octahedral C4v crystal field that stabilizes the low-spin Mn(IV)-oxo intermediates. Understanding reaction intermediates provides a foundation for active electrocatalysts’ design, but it remains elusive for heterogeneous electrocatalysts. Here, the authors report the spectroscopic characterization of low-spin Mn(IV)-oxo as the active intermediates during electrochemical water oxidation.

Triggering the lattice oxygen oxidation mechanism is crucial for improving oxygen evolution reaction (OER) performance, because it could bypass the scaling relation limitation associated with the conventional adsorbate evolution mechanism through the directly formation of oxygen-oxygen bond. High-valence transition metal sites are favorable for activating the lattice oxygen, but the deep oxidation of pre-catalysts suffers from a high thermodynamic barrier. Here, taking advantage of the Jahn-Teller (J-T) distortion induced structural instability, we incorporate high-spin Mn3+ (t2g3eg1) dopant into Co4N. Mn dopants enable a surface structural transformation from Co4N to CoOOH, and finally to CoO2, as observed by various in-situ spectroscopic investigations. Furthermore, the reconstructed surface on Mn doped Co4N triggers the lattice oxygen activation, as evidenced experimentally by pH-dependent OER, tetramethylammonium cation adsorption and on-line electrochemical mass spectrometry measurements of 18O-labelled catalysts. In general, this work not only offers the introducing J-T effect approach to regulate the structural transition, but also provides an understanding about the influence of catalyst's electronic configuration on determining the reaction route, which may inspire the design of more efficient catalysts with activated lattice oxygen.

To systematically investigate the influence of the number of [AO3] layers in the unit cell of hexagonal perovskite oxide on the oxygen evolution reaction performance, we successfully synthesized the three new hexagonal perovskite oxides 2H-BaCo0.9Ru0.1O3-δ, 6H-BaCo0.9Ru0.1O3-δ, and 10H-BaCo0.9Ru0.1O3-δ with the same element composition but different [BaO3] layers via the sol-gel method. Here, 2H, 6H, and 10H refer to the number of [BaO3] layers contained in the unit cell of the BaCo0.9Ru0.1O3-δ system. Experimentally, 10H-BaCo0.9Ru0.1O3-δ, featuring ten layers of [BaO3], exhibits optimal electrochemical activity among the three oxide catalysts, and in situ Raman results under various bias voltages confirm its ability to maintain a high surface crystal structural stability. Notably, as the number of [BaO3] layers increases, the effective magnetic moments and the valence state of surface Co ions in these three catalysts also increase, with the spin configuration of the surface Co ions being in a high-spin state. More importantly, DFT calculations provide the evolution rules of the p-band center (εp) with the number of [BaO3] layers, predicting the electrochemical performance of the BaCo0.9Ru0.1O3-δ system with different [BaO3] layers. Our experimental results offer a distinctive perspective for the future design, synthesis, and application of hexagonal perovskite oxides in electrocatalysis.

Metal-organic frameworks (MOFs) with conjugation carboxylate ligands as electrocatalysts can significantly improve oxygen evolution reaction (OER), but the role of π-interaction on the reactive sites of OER is often neglected. We intend to unravel the mechanism of how π-interaction enhances OER performance. The results of Rietveld refinement, density functional theory (DFT) calculations, and in-situ Raman spectra show that π-interaction can efficiently modulate the local spin configuration of metal centers, facilitate γ-Ni1-xFexOOH active species with high-valence Ni sites modified by high-spin Fe, accelerate electron transfer, optimize the d-band center together with the beneficial rate-determining step of OER. NiFe-BPDC MOFs/NF with 0.8559 eV π-interaction energy generated γ-Ni1-xFexOOH in only 60 s at 1.4 V, demonstrating that π-interaction promotes the rapid generation of highly active reactive sites. Furthermore, the results of in-situ Raman and electron paramagnetic resonance (EPR) spectra reveal that the deprotonation and deoxygenation steps of OER are accompanied by changes in the oxidation state of metal ions and the generation of oxygen vacancies on the surface of catalysts. In addition, NiFe-BPDC MOFs/NF rapidly completes the deprotonation and deoxygenation steps, and it requires only 288 mV overpotential to reach 100 mA/cm2 with 100 h of stability, suggesting promising industrial application.

Layered double-hydroxide (LDH) has been considered an important class of electrocatalysts for the oxygen evolution reaction (OER), but the adsorption-desorption behaviors of oxygen intermediates on its surface still remain unsatisfactory. Apart from transition-metal doping to solve this electrocatalytic problem of LDH, rare-earth (RE) species have sprung up as emerging dopants owing to their unique 4f valence-electronic configurations. Herein, the Er is chosen as a RE model to improve OER activity of LDH via constructing nickel foam supported Er-doped NiFe-LDH catalyst (Er-NiFe-LDH@NF). The optimal Er-NiFe-LDH@NF exhibits a low overpotential (191 mV at 10 mA cm-2 ), high turnover frequency (0.588 s-1 ), and low activation energy (36.03 kJ mol-1 ), which are superior to Er-free sample. Electrochemical in situ Raman spectra reveal the facilitated transition of Ni-OH into Ni-OOH for promoted OER kinetics through the Er doping effect. Theoretical calculations demonstrate that the introduction of Er facilitates the spin crossover of valence electrons by optimizing the d band center of NiFe-LDH, which leads to the GO -GHO closer to the optimal activity of the kinetic OER volcano by balancing the bonding strength of *O and *OH. Moreover, the Er-NiFe-LDH@NF presents high practicability in electrochemical water-splitting devices with a low driving potential of and a well-extended driving period.

Sustainable electrosynthesis of H 2 O 2 via two‐electron oxygen reduction reaction on Ni single atom catalysts (SACs) offers a promising alternative to the traditional anthraquinone technology. However, the limited understanding of the structure‐activity relationship of Ni SAC in the oxygen reduction reaction hinders the rational design of high‐performance catalysts for industrially relevant H 2 O 2 production. Herein, we report a series of heterogeneous molecular Ni‐N 2 O 2 catalysts (Ni‐N 2 O 2 HMCs) with precisely modulated electronic structure through non‐first coordination shell engineering. This strategy systematically reveals the intrinsic correlation among electronic configuration (oxidation/spin state), electrochemical stability, and catalytic performance. The optimized low‐spin Ni‐DPP HMC with extended conjugation achieves >90% selectivity for H 2 O 2 across a wide potential range (0.7–0.2 V vs RHE), reaching 97% at 0.5 V, and delivers a record‐high production rate of 52.13 mol g cat −1 h −1 at an industrially relevant current density of 800 mA cm −2 in a flow cell. In situ spectroscopy and DFT calculations reveal that Ni‐DPP modulates the *OOH adsorption, optimizing the balance between activity and selectivity. These findings provide key insights for the rational design of SACs for efficient H 2 O 2 electrosynthesis.

The regulation of electronic structure is intricately linked to the intrinsic activity of oxygen reduction. Herein, a strategy for electronic structure modulation induced by bimetallic push–pull electronic effects in dual‐atom catalysts (Fe,Ni/N‐C@NG) is developed. Experiments and theoretical analysis reveal that Fe sites exhibit favorable bonding behaviors (Fe–O: dxz‐p, dyz‐p, and dz2‐p) and spin configurations, which can enable rapid desorption of *OH and thus enhance the intrinsic activity of oxygen reduction. In situ monitoring techniques and Gibbs free energy diagram further demonstrate that the adjacent Ni could serve as second active center to participate in oxygen reduction. The Fe,Ni/N‐C@NG exhibits enhanced oxygen reduction reaction activity and excellent stability. Meanwhile, the assembled Zn–air battery maintains stability for over 300 h with a small voltage gap. This study provides multiple insights into the orbital scale laws of oxygen reduction.

Single atom catalysts (SACs) have been attracting extensive attention in electrocatalysis because of their unusual structure and extreme atom utilization, but the low metal loading and unified single site induced scaling relations may limit their activity and practical application. Tailoring of active sites at the atomic level is a sensible approach to break the existing limits in SACs. In this review, SACs were first discussed regarding carbon or non-carbon supports. Then, five tailoring strategies were elaborated toward improving the electrocatalytic activity of SACs, namely strain engineering, spin-state tuning engineering, axial functionalization engineering, ligand engineering, and porosity engineering, so as to optimize the electronic state of active sites, tune d orbitals of transition metals, adjust adsorption strength of intermediates, enhance electron transfer, and elevate mass transport efficiency. Afterward, from the angle of inducing electron redistribution and optimizing the adsorption nature of active centers, the synergistic effect from adjacent atoms and recent advances in tailoring strategies on active sites with binuclear configuration which include simple, homonuclear, and heteronuclear dual atom catalysts (DACs) were summarized. Finally, a summary and some perspectives for achieving efficient and sustainable electrocatalysis were presented based on tailoring strategies, design of active sites, and in situ characterization.

The 5-substituted 2-aryliminopyrrolyl ligand precursors of the type 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]-1 H-pyrrole (R = 2,6-Me2-C6H3 (1a), 2,4,6-iPr3-C6H2 (1b), 2,4,6-Ph3-C6H3 (1c; reported in this work), anthracen-9-yl (1d), CPh3 (1e; reported in this work)) were treated with K[N(SiMe3)2] in toluene to yield the respective 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]pyrrolyl potassium salts 2a-e in high yields. The paramagnetic 15-electron Co(II) complexes of the type [Co{κ2 N,N'-5-R-NC4H2-2-C(H)═N(2,6-iPr2-C6H3)}(Py)Cl] (3a-e; Py = pyridine) were prepared by salt metathesis of CoCl2(Py)4 with the respective potassium salts 2a-e in moderate to good yields. When the CoCl2(THF)1.5 precursor was combined with the in situ prepared sodium salt of ligand precursor 1b, the trinuclear complex [Co{κ2 N, N'-5-(2,4,6-iPr3-C6H2)-NC4H2-2-C(H)═N(2,6-iPr2-C6H3)}(μ-Cl)]2[(μ-Cl)2Co(THF)2] (4) was obtained in high yields. Complexes 3a-e have high-spin electronic configurations both in solution and in the solid state. X-ray diffraction studies of complexes 3a,e confirmed distorted tetrahedral coordination geometries. Complex 4, on the other hand, is a linear trinuclear Co(II)-Co(II)-Co(II) complex with two terminal distorted tetrahedral four-coordinate sites and a central octahedral six-coordinate site, all in the high-spin state, S = 3/2, as confirmed by the magnetization measurements and DFT calculations. Solid-state magnetic measurements in both complexes 3a and 4 point to paramagnetic behavior with a significant contribution of spin-orbit coupling. Additionally, intramolecular antiferromagnetic coupling of the adjacent cobalt atoms is observed in 4. The Co(II) family 3a-d, on activation with K(HBEt3), catalyzed the hydroboration of several α-olefins with pinacolborane, in good to high yields (50-80%). This system almost exclusively yielded the anti-Markovnikov (a-Mk) addition product, except when styrene was used, where the selectivity in the Markovnikov (Mk) product increased with increasing steric bulkiness of the 5-R-2-iminopyrrolyl substituent, with the a-Mk:Mk molar ratio varying from 2.33:1 (3a, R = 2,6-Me2-C6H3) to 0.75:1 (3c, R = 2,4,6-Ph3-C6H3). Preliminary mechanistic studies indicate that the activation by K(HBEt3) gave rise to a Co(I) species, the catalyst system likely following an oxidative addition pathway.

No abstract available

No abstract available

Tracking changes in the chemical state of transition metals in alkali-ion batteries is crucial to understanding the redox chemistry during operation. X-ray absorption spectroscopy (XAS) is often used to follow the chemistry through observed changes in the chemical state and local atomic structure as a function of the state-of-charge (SoC) in batteries. In this study, we utilize an operando X-ray emission spectroscopy (XES) method to observe changes in the chemical state of active elements in batteries during operation. Operando XES and XAS were compared by using a laboratory-scale setup for four different battery systems: LiCoO2 (LCO), Li[Ni1/3Co1/3Mn1/3]O2 (NMC111), Li[Ni0.8Co0.1Mn0.1]O2 (NMC811), and LiFePO4 (LFP) under a constant current charging the battery in 10 h (C/10 charge rate). We show that XES, despite narrower chemical shifts in comparison to XAS, allows us to fingerprint the battery SOC in real time. We further demonstrate that XES can be used to track the change in net spin of the probed atoms by analyzing changes in the emission peak shape. As a test case, the connection between net spin and the local chemical and structural environment was investigated by using XES and XAS in the case of electrochemically delithiated LCO in the range of 2–10% lithium removal.

The use of ceria as catalyst in hydrogenation reactions is a recent trend, as they were uncovered to be active on a number of substrates, including alkynes, alkenes, and enones. While some studies focused on the use of well‐defined shapes, others emphasized the interest of defective structures. Overall, the meeting point of these studies is the need to characterize the surface reactivity vs. H2, by considering a number of interesting textures (films, nanopowders with various grain size or porosity), using monitoring techniques that preserve the original features of the materials. A key question is in particular to assess the possibility to form surface hydride through homolytic H2 splitting at cerium sites rather than at the oxygen one, a route recently highlighted as plausible. To address this question on small crystallites of CeO2, we designed a low‐temperature synthetic route for nanorods with an average grain size of 10 nm. Then, we employed near‐ambient‐pressure X‐ray photoelectron spectroscopy as an operando tool to monitor the cerium surface oxidation state during the initial annealing of the nanopowders, followed by exposure to a moderate pressure of H2 (0.52 mbar). We demonstrate that H2 homolytic splitting at cerium sites is the main activation process on this surface at 100 °C, leading to the oxidation of ca. 30 % of the surface cerium atoms from Ce3+ to Ce4+. The surface hydride species were however not stable at 250 °C, H2 was released, and cerium reduced back to Ce3+. A similar mechanism was observed on a defective ceria material obtained by calcination of CeO(OH)2, with comparable intensities. Overall, we report here CeO2 nanorods, exposing predominantly {100} and {110} facets, as showing an interesting surface reactivity for potential application in hydrogenation reactions, and we expose a straight operando methodology to delineate suitable temperatures to be used.

Establishing mechanistic understanding of crystallization processes at the molecular level is challenging, as it requires both the detection of transient solid phases and monitoring the evolution of both liquid and solid phases as a function of time. Here, we demonstrate the application of dynamic nuclear polarization (DNP) enhanced NMR spectroscopy to study crystallization under nanoscopic confinement, revealing a viable approach to interrogate different stages of crystallization processes. We focus on crystallization of glycine within the nanometric pores (7–8 nm) of a tailored mesoporous SBA-15 silica material with wall-embedded TEMPO radicals. The results show that the early stages of crystallization, characterized by the transition from the solution phase to the first crystalline phase, are straightforwardly observed using this experimental strategy. Importantly, the NMR sensitivity enhancement provided by DNP allows the detection of intermediate phases that would not be observable using standard solid-state NMR experiments. Our results also show that the metastable β polymorph of glycine, which has only transient existence under bulk crystallization conditions, remains trapped within the pores of the mesoporous SBA-15 silica material for more than 200 days.

Transition metal oxides are promising electrocatalysts for water oxidation, i.e., the oxygen evolution reaction (OER), which is critical in electrochemical production of non-fossil fuels. The involvement of oxidation state changes of the metal in OER electrocatalysis is increasingly recognized in the literature. Tracing these oxidation states under operation conditions could provide relevant information for performance optimization and development of durable catalysts, but further methodical developments are needed. Here, we propose a strategy to use single-energy X-ray absorption spectroscopy for monitoring metal oxidation-state changes during OER operation with millisecond time resolution. The procedure to obtain time-resolved oxidation state values, using two calibration curves, is explained in detail. We demonstrate the significance of this approach as well as possible sources of data misinterpretation. We conclude that the combination of X-ray absorption spectroscopy with electrochemical techniques allows us to investigate the kinetics of redox transitions and to distinguish the catalytic current from the redox current. Tracking of the oxidation state changes of Co ions in electrodeposited oxide films during cyclic voltammetry in neutral pH electrolyte serves as a proof of principle.

Here, a microfluidic paper‐based analytical device (µ‐PADs) with editable electron configuration and conductivity is proposed for sensitive point‐of‐care (POC) detection of acetamiprid (ACE). The CdS‐protected CsPbX3:Mn (X = Cl, Br) halide perovskite (CPCBM/CdS) quantum dots (QDs) with a core/shell structure are prepared for the first time. This advancement not only addresses the challenge of the inherent water instability of perovskites but also imparts spin‐related charge‐transfer properties to the composite material. Additionally, a simple magnetic stimulation method is employed to rearrange the spin electron occupation in perovskites, effectively enhancing the charge separation efficiency in paper‐based PEC (µ‐PEC) sensing systems. The underlying mechanism is systematically investigated using density functional theory simulations and ultrafast transient absorption spectroscopy. These studies revealed a spin‐dependent reaction pathway and the carrier lifetime extended to 4244 ps under a magnetic field (MF), which is 2.2 times longer than that of the pristine perovskite. As a proof‐of‐concept application, a µ‐PEC sensor is developed for sensitive POC monitoring of ACE in environmental samples with a low detection limit of 23 fm. This study shows that manipulating spin‐polarized electrons in photosensitive semiconductors provides an effective strategy to enhance sensing sensitivity, which holds great prospects for future environmental detection and health monitoring.

No abstract available

The structural transition of ZIF-8 under N2 gas adsorption/desorption processes has been already investigated using various characterization techniques. This study demonstrates that electron paramagnetic resonance (EPR) spectroscopy is an alternative and powerful method that provides valuable local structure insights into the gate opening from ambient pressure (AP) to high pressure (HP) structural phases of the ZIF-8 framework during N2 gas adsorption/desorption. Our in situ EPR experiments reveal distinct distortions in the environment of the tetrahedral metal ion framework sites for Mn2+ and Cu2+ dopants, demonstrating their different responsiveness to the gate opening transition. We were able to detect the AP to HP structural transition by monitoring the changes in the zero-field splitting of the paramagnetic Mn2+ (S = 5/2) probe ions. The results are complemented by employing Cu2+ (S = 1/2) centres as alternative spin probes where the Cu2+g-tensor and hyperfine parameters change likewise at the AP to HP structural transition. Our findings validate the use of paramagnetic centres as spin probes for locally monitoring the N2 gas-induced structural changes within the ZIF-8 framework. Notably, in situ EPR spectroscopy was successfully utilised to observe such transitions during N2 gas adsorption/desorption processes in ZIF-8. The acquired spectroscopic results are consistent with previous reports on the gate-opening of ZIF-8, confirming the reliability and potential of this local spectroscopic method.

Manipulating electronic polarizations such as ferroelectric or spin polarizations has recently emerged as an effective strategy for enhancing the efficiency of photocatalytic reactions. This study demonstrates the control of electronic polarizations modulated by ferroelectric and magnetic approaches within a two-dimensional (2D) layered crystal of copper indium thiophosphate (CuInP2S6) to boost the photocatalytic reduction of CO2. We investigate the substantial influence of ferroelectric polarization on the photocatalytic CO2 reduction efficiency, utilizing the ferroelectric-paraelectric phase transition and polarization alignment through electrical poling. Additionally, we explore enhancing the CO2 reduction efficiency by harnessing spin electrons through the synergistic introduction of sulfur vacancies and applying a magnetic field. Several advanced characterization techniques, including piezoresponse force microscopy, ultrafast pump–probe spectroscopy, in situ X-ray absorption spectroscopy, and in situ diffuse reflectance infrared Fourier transformed spectroscopy, are performed to unveil the underlying mechanism of the enhanced photocatalytic CO2 reduction. These findings pave the way for manipulating electronic polarizations regulated through ferroelectric or magnetic modulations in 2D layered materials to advance the efficiency of photocatalytic CO2 reduction.

Electrocatalytic nitrate reduction reaction offers an effective route for ammonia synthesis and actual wastewater treatment. Despite some important achievements, the progress is still low than expected, especially in low-concentration nitrate, mostly because of slow hydrogenation kinetics and interfering substances. In this work, we presented that, by engineering spin orbital orientation, a carbon-encapsulated FeP/Fe3O4 heterojunctions (FeP/Fe3O4@C) enabled ultrafast and stable NH3 electrosynthesis from low-concentration nitrate. In-situ characterization and theoretical calculation confirmed that FeP/Fe3O4 heterojunctions induced spin orbit splitting of Fe, resulting in electron transition from low spin to high spin. The resulted non-degenerate orbitals caused the energy levels shift up and guided the electron migration from FeP to Fe3O4, which thus activated additional 3d orbital electron states. This spin orbital orientation further optimized the chemisorption properties of nitrogen-oxygen intermediates and H* spillover, thus accelerating hydrogenation kinetics for ultrafast NH3 electrosynthesis. Meanwhile, FeP/Fe3O4@C electrocatalyst alleviated the phosphate poisoning of active metal sites during industrial wastewater treatment, demonstrating excellent anti-interference capability and environmental sustainability for real application. This work by modulating the "charge-spin-orbit" structure of active sites provided a new strategy for rational design of high-performance electrocatalysts for various electrocatalytic reactions.

Triggering rapid reconstruction reactions holds the potential to approach the theoretical limits of the oxygen evolution reaction (OER), and spin state manipulation has shown great promise in this regard. In this study, the transition of Fe spin states from low to high was successfully achieved by adjusting the surface electronic structure of pentlandite. In-situ characterization and kinetic simulations confirmed that the high-spin state of Fe promoted the accumulation of OH- on the surface and accelerated electron transfer, thereby enhancing the kinetics of the reconstruction reaction. Furthermore, theoretical calculations revealed that the lower d-band center of high-spin Fe optimized the adsorption of active intermediates, thereby enhancing the reconstruction kinetics. Remarkably, pentlandites with high-spin Fe exhibited ultra-low overpotential (245 mV @ 10 mA cm-2) and excellent stability. These findings provided new insights for the design and fabrication of highly active OER electrocatalysts.

No abstract available

The splitting of dinitrogen into nitride complexes emerged as a key reaction for nitrogen fixation strategies at ambient conditions. However, the impact of auxiliary ligands or accessible spin states on the thermodynamics and kinetics of N-N cleavage is yet to be examined in detail. We recently reported N-N bond splitting of a {Mo(μ2:η1:η1-N2)Mo}-complex upon protonation of the diphosphinoamide auxiliary ligands. The reactivity was associated with a low-spin to high-spin transition that was induced by the protonation reaction in the coordination periphery, mainly based on computational results. Here, this proposal is evaluated by an XAS study of a series of linearly N2 bridged Mo pincer complexes. Structural characterization of the transient protonation product by EXAFS spectroscopy confirms the proposed spin transition prior to N-N bond cleavage.

To achieve high selectivity in the transformation from peroxymonosulfate to singlet oxygen, adaptive tuning of atomic spin state as the peroxymonosulfate structure varied is crucial. The angstrom confinement can effectively tune spin state, but developing an adaptive angstrom‐confined atomic system is challenging. Angstrom‐confined cobalt (Co) manganese (Mn) dual single atoms within flexible 2D carbon nitride interlayer are constructed to drive adaptive tuning of spin state by changing atomic coordination under angstrom confinement. The in situ characterizations and density functional theory calculations showed that medium‐spin Co in Co─N4 absorbed electrons after the adsorption of peroxymonosulfate on CoMn dual single‐atom sites and then cleaved O─H of peroxymonosulfate to facilitate *SO5 generation, while the introduction of *SO5 increased interlayer distance and then cleaved Co─N and Mn─N, resulting in the spin state transition from medium to high. Subsequently, the high‐spin Co and Mn in Co─N2 and Mn─N2 desorbed the *O2 from *SO5, restoring the initial medium spin state. The adaptive spin state transition enhanced 38.6‐fold singlet oxygen yield compared to the unconfined control. The proposed angstrom‐confined diatomic strategy is applicable to serial diatomic catalysts, providing an efficient and universal design scheme for singlet oxygen‐mediated selective wastewater treatment technology at the atomic level.

Spin-state transition is a vital factor that dominates catalytic processes, but unveiling its mechanism still faces the great challenge of the lack of catalyst model systems. Herein, we propose that the {Fe-Pt} Hofmann clathrates, whose dynamic spin-state transition of metal centers can be chemically manipulated through iodine treatment, can serve as model systems in the spin-related structural-catalytic relationship study. Taking the photocatalytic synthesis of H2O2 as the basic catalytic reaction, when the spin state of Fe(II) in the clathrate is high spin (HS), sacrificial agents are indispensable to the photosynthesis of H2O2 because only the photocatalytic oxygen reduction reaction (ORR) occurs; when it is low spin (LS), both the ORR and water oxidation reaction (WOR) can take place, enabling a high H2O2 photosynthesis rate of 66 000 μM g-1 h-1 under visible-light irradiation. In situ characterizations combined with density functional theory calculations confirmed that, compared with the HS-state counterpart, the LS state can induce strong charge transfer between the LS Fe(II) and the iodide-coordinating Pt(IV) in the polymer and reduce the energy barriers for both the ORR and WOR processes, dominating the on-off switching upon the photosynthesis of H2O2 in O2-saturated water. What's more, the one-pot tandem reactions were conducted to utilize the synthesized H2O2 for transforming the low-value-added sodium alkenesulfonates into value-added bromohydrin products with decent conversion rates. This work provides a pioneering investigation into on-off switching the photocatalytic overall reaction through manipulating the metallic spin-state transition in spin-crossover systems.

Oxygen reduction reaction (ORR) kinetics are closely related to the electronic structure of active sites. Herein, a single‐atomic Mn catalyst decorated with adjacent MoP nanocrystals (MoP@MnSAC‐NC) is reported. The decoration of MoP drives the electronic structure transition of Mn sites from low‐spin to high‐spin states through an electronic phosphide‐support interaction. The rearranged electron occupation in 3dxz‐yz and 3dz2 orbitals of Mn sites leads to electrons occupying the σ orbital in Mn─*O2, thereby favoring O2 adsorption to initiate the ORR mechanism. In situ characterizations confirm that Mn 3dz2 orbital occupation state can activate molecular O₂ and optimize the adsorption of the *OOH intermediate. As a result, the MoP@MnSAC‐NC displays an outstanding alkaline ORR half‐wave potential (E1/2 = 0.894 V), excellent peak power densities (173/83 mW cm−2 for liquid/solid‐state Zn‐air batteries, respectively), and long‐term stability (840 h) superior to commercial Pt/C. This work provides profound insights into spintronics‐level engineering, guiding the design of next‐generation high‐performance ORR catalysts.

Transition metal-based catalytic materials are promising pre-catalysts for oxygen evolution reaction (OER), during which the in situ reconstructed metal oxyhydroxides are real active sites. However, a majority of documented pre-catalysts exhibit sluggish reconstruction dynamics, leading to in-complete reconstruction and consequently poor OER activity. Herein, exemplified by Hoffman-type coordination polymer (NiFe-Ni PBA), plasma etching is employed to create cation-anion dual vacancies (Niv and CNv) to promote the rapid and deep reconstruction of NiFe-Ni PBA into defective NiOOH/FeOOH (P-NiOOH/FeOOH) during the activation process. Langmuir probe diagnostics and structural characterizations of NiFe-Ni PBA before and after plasma etching evidence that Niv and CNv are predominantly generated by the bombardment of high-energy ions, whereas elemental nickel will be produced when electron energy exceeds a critical threshold. Density functional theory (DFT) calculations, in situ Raman spectra, and Laviron analysis reveal that the abundant vacancies in plasma-etched NiFe-Ni PBA effectively lower the reconstruction reaction barrier and promote the accumulation of OH− ions during the reconstruction process, enabling faster reconstruction kinetics. As expected, the P-NiOOH/FeOOH exhibits enhanced OER activity with a low overpotential of 220 mV at 10 mA cm−2 and a small Tafel slope of 29.82 mV dec−1 in 1 M KOH. Magnetic test, differential electrochemical mass spectrometry measurement, and DFT calculations illustrate that the improved OER activity can be attributed to the high spin state, optimized d-band center of metal ions, rich oxygen vacancies, and more activated lattice oxygen in P-NiOOH/FeOOH. Moreover, the P-NiOOH/FeOOH also displays splendid catalytic stability up to 850 h.

The poor stability and metal leaching of transition metal-based catalysts for peroxymonosulfate (PMS) activation cause practical challenges in Emerging Contaminants (ECs) degradation. It is necessary to explore non-metallic catalyst with high activity and stability. Herein, carbon-doped graphitic carbon nitride (C-C3N4) is synthesized through sample thermal polymerization. The morphology and chemical structure of C-C3N4 are analyzed in detail through multiple characterizations combining density functional theory (DFT) calculation. The tetracycline (TC) can be nearly 100 % removed in 15 min with the high mineralization rate (∼70 %) in 50 min by C-C3N4/PMS system. The continuous reaction and recycle using experiments exhibit the excellent stability of C-C3N4 and the tetracycline (TC) remove rate still exceeds 80 % after 360 min. The high applicability of C-C3N4 to different water sources, anions and pollutants is also tested. Qualitative and quantitative analysis of reactive oxygen species (ROSs) proves the enhanced generation of •OH, SO4•-, 1O2. C doping leads to the electron spin polarization and regulates electronic structure thus enhances the electron transfer between PMS and C-C3N4. In situ analysis combining DFT calculation identifies that doped C is the active site for PMS activation and dual-site adsorption of PMS on doped C and N‒(C)2 greatly decreases the energy barrier for •OH generation (from 1.52 to 0.27 eV). Fukui function calculation combining the intermediate detection by LC-MS concludes the detailed degradation pathway. This study provides a valuable insight for the development of efficient metal-free catalysts and the deep degradation of ECs through Fenton-like catalysis.

The inherent stress in heterostructures destabilizes the crystal lattice, distorts intermediate adsorption, and increases the energy barrier of the potential‐determining step in anion exchange membrane water electrolyzers (AEMWE). Herein, an innovative liquid nitrogen quenching strategy is developed to induce a high‐spin to low‐spin transition in NiS x ‐based heterostructures through nitrogen incorporation, where the electron‐withdrawing effect modifies the local electronic valence state to optimize intermediate adsorption/desorption energetics and significantly reduce the energy barrier of the potential‐determining step. Consequently, the low‐spin state NiS x nanosheets demonstrate superior electrocatalytic performance, delivering low overpotentials of 78.1 mV for hydrogen evolution reaction (HER) and 210.0 mV for oxygen evolution reaction (OER) at ±10 mA cm −2 , respectively, while enabling efficient overall water splitting with a cell voltage of 1.59 V at 10 mA cm −2 . Meanwhile, the AEMWE with LNQ‐NiS x /NF anode maintains stable operation at 1.25 A cm −2 for over 150 h, showing merely 1.13 mV h −1 potential degradation. In situ characterization confirms robust structural stability and enhanced adsorption of reactive intermediates, while density functional theory (DFT) calculations verify the critical role of low‐spin state in reducing energy barriers. Overall, this work provides a rational design strategy for advanced water electrolyzer electrocatalysts by elucidating the spin state‐activity relationship.

Transition metal‐based materials exhibit a broad range of catalytic activities in numerous electrochemical processes. Their displayed catalytic functions rely essentially on their distinctive electronic structures, changes of which play pivotal roles in dictating reaction dynamics within many electrochemical devices. Nevertheless, accurately probing electronic structure changes, especially in real‐time, of active materials remains a formidable challenge. In this work, a viable approach to achieve it within a CoC2O4/Li model system by employing a combined microscopic is demonstrated, spectroscopic analysis, plus a unique operando magnetometry technique. The findings reveal that upon completion of the conventional conversion of CoC2O4, a surface‐dominated capacitance emerges at the Co/Li2C2O4 interface owing to the injection of spin‐polarized electrons. Subsequently, the decomposition of Li2C2O4 proceeds through the releasing of the spin‐polarized electrons from Co, which, therefore serve as a catalyst leading to further discharge products. Such real‐time monitoring of electron transfer is realized by in situ monitoring electronic structure changes of Co, manifested by its intriguing magnetization alterations during the process. This work highlights a novel characterization tool that provides a solid explanation for the commonly observed large capacities in this type of materials and sheds light on design rules and selection guidance of materials for high‐performance electrochemical energy storage systems.

Developing efficient, environmentally friendly and cost-effective non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is essential to alleviate the energy crisis and environmental pollution. Herein, we report a simple and practical method to prepare non-precious metal catalysts, namely iron-modulated Ni3S2 (Fe-Ni3S2/NF) on nickel foam, by growing a Ni-MOF directly on 3D porous conductive nickel foam, followed by the formation of Ni-MOF-based Prussian blue analogs (Ni-MOF@PBA) via in situ cation exchange reactions, which are further sulfidated to iron-modulated Ni3S2. Based on a series of characterization results, it is confirmed that iron acts as a modulator at the Ni active site, leading to electron depletion, thereby modulating the electron spin state and optimizing the binding energy of key reaction intermediates, resulting in highly exposed active sites and acceleration of OER reaction kinetics. The synthesized Fe-Ni3S2/NF exhibits excellent activity in alkaline media, which needs overpotentials of only 232 mV and 287 mV to drive current densities of 10 mA cm-2 and 50 mA cm-2, respectively. Additionally, Fe-Ni3S2/NF exhibits excellent stability for at least 24 h during the OER process. This work presents a rational design and synthesis of transition metal-based catalysts with nanocone structures, providing a new strategy for assembling advanced materials and insights for exploring various energy storage and conversion systems.

Cu-and Fe-exchanged zeolites have been widely investigated for their applicability in selective partial oxidation of CH 4 and abatement of environmentally harmful nitrogen oxides. However, the differentiation between spectator and active sites is cumbersome due to their dynamic co-existence

: The heterogeneous speciation of ion-exchanged zeolites hinders a rational understanding of their reactivity. This is particularly the case for Fe-containing zeolites that are widely used in both the activation and decomposition of N 2 O. Herein, we explored the reactive structure of Fe ions in the small pore zeolite SSZ-13 utilizing a combination of operando techniques, including diffuse reflectance UV − vis (DRUV) and infrared (DRIFTS) spectroscopy, as well as electron paramagnetic resonance spectroscopy (EPR), showcasing complementary sensitivity to different structural properties of the catalyst. Coupling these techniques with modulated excitation (ME) and phase-sensitive detection (PSD) enabled site-selective tracking of the behavior of Fe ions and demonstrated (i) the redox reaction of specific Fe ions in six-membered rings (Fe 6MR2+ ↔ Fe 6MR3+ − O − ) during oxidation (OHC) and reduction (RHC) half-cycles and (ii) the rate-determining nature of the RHC. The PSD response in these spectroscopic experiments emerged as a suitable descriptor of the Fe-SSZ-13 activity toward N 2 O decomposition. Changes in Fe speciation obtained by synthesis influenced the capability of the Fe ions to undergo this site-selective redox-mediated mechanism. The direct correlation between the redox kinetics of monomeric Fe sites in the six-membered rings (Fe 6MR , 107 ± 11 kJ mol − 1 ) and the reaction rate of N 2 O decomposition (113.6 ± 16 kJ mol − 1 ) allowed us to unambiguously assign the global reactivity of Fe-SSZ-13 to these specific Fe

Understanding hydrocarbon generation in the zeolite-catalysed conversions of methanol and methyl chloride requires advanced spectroscopic approaches to distinguish the complex mechanisms governing C–C bond formation, chain growth and the deposition of carbonaceous species. Here operando photoelectron photoion coincidence (PEPICO) spectroscopy enables the isomer-selective identification of pathways to hydrocarbons of up to C14 in size, providing direct experimental evidence of methyl radicals in both reactions and ketene in the methanol-to-hydrocarbons reaction. Both routes converge to C5 molecules that transform into aromatics. Operando PEPICO highlights distinctions in the prevalence of coke precursors, which is supported by electron paramagnetic resonance measurements, providing evidence of differences in the representative molecular structure, density and distribution of accumulated carbonaceous species. Radical-driven pathways in the methyl chloride-to-hydrocarbons reaction(s) accelerate the formation of extended aromatic systems, leading to fast deactivation. By contrast, the generation of alkylated species through oxygenate-driven pathways in the methanol-to-hydrocarbons reaction extends the catalyst lifetime. The findings demonstrate the potential of the presented methods to provide valuable mechanistic insights into complex reaction networks. The conversions of methanol or methyl chloride over zeolite catalysts are promising processes to produce valuable hydrocarbons, but their mechanisms are still not fully understood. Now these are evaluated using operando photoelectron photoion coincidence spectroscopy, which enables the direct observation of elusive intermediates such as methyl radicals or ketene.

The development of surface-immobilized molecular redox catalysts is an emerging research field with promising applications in sustainable chemistry. In electrocatalysis, paramagnetic species are often key intermediates in the mechanistic cycle but are inherently difficult to detect and follow by conventional in situ techniques. We report a new method, operando film-electrochemical electron paramagnetic resonance spectroscopy (FE-EPR), which enables mechanistic studies of surface-immobilized electrocatalysts. This technique enables radicals formed during redox reactions to be followed in real time under flow conditions, at room temperature and in aqueous solution. Detailed insight into surface-immobilized catalysts, as exemplified here through alcohol oxidation catalysis by a surface-immobilized nitroxide, is possible by detecting active-site paramagnetic species sensitively and quantitatively operando, thereby enabling resolution of the reaction kinetics. Our finding that the surface electron-transfer rate, which is of the same order of magnitude as the rate of catalysis (accessible from operando FE-EPR), limits catalytic efficiency has implications for the future design of better surface-immobilized catalysts. Although surface-bound molecular catalysts offer well-defined active sites on heterogeneous supports, it is challenging to identify key radical intermediates in the reaction mechanism. Now, a characterization method has been developed that combines film electrochemistry and EPR spectroscopy to track radical intermediates in real time, exemplified by alcohol oxidation with a surface-immobilized nitroxide.

The intermediacy of alkoxy radicals in cerium-catalyzed C-H functionalization via H-atom abstraction has been unambiguously confirmed. Catalytically relevant Ce(IV)-alkoxide complexes have been synthesized and characterized by X-ray diffraction. Operando electron paramagnetic resonance and transient absorption spectroscopy experiments on isolated pentachloro Ce(IV) alkoxides identified alkoxy radicals as the sole heteroatom-centered radical species generated via ligand-to-metal charge transfer (LMCT) excitation. Alkoxy-radical-mediated hydrogen atom transfer (HAT) has been verified via kinetic analysis, density functional theory (DFT) calculations, and reactions under strictly chloride-free conditions. These experimental findings unambiguously establish the critical role of alkoxy radicals in Ce-LMCT catalysis and definitively preclude the involvement of chlorine radical. This study has also reinforced the necessity of a high relative ratio of alcohol vs Ce for the selective alkoxy-radical-mediated HAT, as seemingly trivial changes in the relative ratio of alcohol vs Ce can lead to drastically different mechanistic pathways. Importantly, the previously proposed chlorine radical-alcohol complex, postulated to explain alkoxy-radical-enabled selectivities in this system, has been examined under scrutiny and ruled out by regioselectivity studies, transient absorption experiments, and high-level calculations. Moreover, the peculiar selectivity of alkoxy radical generation in the LMCT homolysis of Ce(IV) heteroleptic complexes has been analyzed and back-electron transfer (BET) may have regulated the efficiency and selectivity for the formation of ligand-centered radicals.

Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for in situ/operando tracking of catalytic reactions that involve paramagnetic species either as a catalyst (e.g. transition metal ions or defects), reaction intermediates (radicals) or poisoning agents such as coke. This article provides a summary of recent experimental examples and developments in resonator design as well as detection schemes that were carried out in our group. Opportunities for applying this technique are illustrated by examples, including studies of transition metal exchanged zeolites and metal-free zeolites as well as metal oxide catalysts. The inherent limitations of EPR applied at high temperatures are discussed, as well as strategies in reducing or lifting these restrictions are evaluated and ideas for future improvements and methodologies are discussed.

Cu-exchanged mordenite (MOR) is a promising material for partial CH4 oxidation. The structural diversity of Cu species within MOR makes it difficult to identify the active Cu sites and to determine their redox and kinetic properties. In this study, the Cu speciation in Cu-MOR materials with different Cu loadings has been determined using operando electron paramagnetic resonance (EPR) and operando ultraviolet-visible (UV-Vis) spectroscopy as well as in situ photoluminescence (PL) and Fourier-transform infrared (FTIR) spectroscopy. A novel pathway for CH4 oxidation involving paired [CuOH]+ and bare Cu2+ species has been identified. The reduction of bare Cu2+ ions facilitated by adjacent [CuOH]+ demonstrates that the frequently reported assumption of redox-inert Cu2+ centers does not generally apply. The measured site-specific reaction kinetics show that dimeric Cu species exhibit a faster reaction rate and a higher apparent activation energy than monomeric Cu2+ active sites highlighting their difference in the CH4 oxidation potential.

No abstract available

Paramagnetic molybdenum compounds are of great interest in inorganic chemistry and metalloenzyme catalysis. Electron paramagnetic resonance (EPR) spectroscopies that determine hyperfine coupling constants (HFCs) and g‐tensor values are essential for investigating the electronic structure of these compounds, but require support from accurate quantum chemical approaches. Here, a database of Mo(V) complexes with well‐defined structures and EPR parameters is presented, and optimal quantum chemical protocols for 95Mo HFCs and g‐values are investigated. It is shown that unmodified segmented all‐ electron relativistically contracted (SARC) all‐electron basis sets can produce converged results for HFCs and g‐values with the exact‐2‐component (X2C) Hamiltonian. The dependence of EPR parameters on the functional is studied in detail. Double‐hybrid functionals and global hybrids with high exact exchange are top performers for 95Mo HFCs, with PBE0‐DH achieving the best agreement with experiment. Comparison of density functional theory (DFT)‐derived HFCs with values obtained by coupled cluster theory with the domain‐based local pair natural orbital approach (DLPNO‐CCSD) shows that DFT remains the method of choice for the present set of compounds. Smaller differentiation among functionals is observed for g‐tensors, although PBE0‐DH is still a top performer and can be recommended as the most reliable approach overall for describing both valence and core properties of Mo compounds.

Laccases are multi‐copper oxidases (MCOs) that oxidize a broad range of substrates while reducing molecular oxygen to water. Although much effort has been made to elucidate the catalytic mechanism of laccases, information about reactive catalytic intermediates during catalysis is not yet fully understood. Herein, hydroquinone (HQ) polymerization catalyzed by prokaryotic small laccase (SLAC) was investigated by electron paramagnetic resonance (EPR) spectroscopy to provide more information on the catalytic mechanism. Briefly, free radical intermediates during the catalysis were investigated by real‐time in situ EPR measurement to monitor the formation and transformation of free radicals. A paramagnetic species was identified which was attributed to a copolymer formed by hydroquinone, benzoquinone, and semiquinone radical. In addition, the low‐temperature EPR spectrum of the trinuclear copper center during catalysis not only revealed tentative rotational motion of the histidine imidazole rings coordinating the TNC upon electron uptake but also provided evidence of the formation of oxygen bridge at TNC during the reaction, represented by the observation of a new type 2 copper component featured larger g// values and smaller A// values. Together, EPR spectroscopic insights into the catalytic intermediates during enzymatic hydroquinone polymerization have extended the knowledge of the biophysical characteristics and catalytic mechanism of SLAC.

Oxidizing species or radicals generated in water are of vital importance in catalysis, the environment, and biology. In addition to several related reactive oxygen species, using electron paramagnetic resonance (EPR), we present a nontrapping chemical transformation pathway to track water radical cation (H2O+•) species, whose formation is very sensitive to the conditioning environments, such as light irradiation, mechanical action, and gas/chemical introduction. We reveal that H2O+• can oxidize the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to the crucial epoxy hydroxylamine (HDMP=O) intermediate, which further reacts with the hydroxyl radical (•OH) for the formation of the EPR-active sextet radical (DMPO=O•). Interestingly, we uncover that H2O+• can react with dimethyl methylphosphonate (DMMP), 2-methyl-2-nitrosopropane (MNP), 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO), and α-phenyl-N-tert-butylnitrone (PBN) which contain a double-bond structure to produce corresponding derivatives as well. It is thus expected that both H2O+• and •OH are ubiquitous in nature and in various water-containing experimental systems. These findings provide a novel perspective on radicals for water redox chemistry.

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Here, we report curvature-induced electron spin catalysis by using solid carbon spheres as catalysts, which were synthesized using positive curvature molecular hexabromocyclopentadiene as a precursor molecule, following a radical coupling mechanism. The curvature spin of carbon is regarded as an overlapping state of σ- and π-radical, which is identified by the inverse Laplace transform of pulse-electron paramagnetic resonance. The growth mechanism of carbon spheres abiding by Kroto's model, is supported by the density functional theory study of thermodynamics and kinetics calculations. The solid carbon spheres present excellent catalytic behaviour of oxidation coupling of amines to form corresponding imines with the conversion of >99%, selectivity of 98.7%, and yield of 97.7%, which is attributed to the predominantly curvature-induced electron spin catalysis of carbon, supported by the calculation of oxygen adsorption energy. This work proposes a view of curvature-induced spin catalysis of carbon, which opens up a research direction for curvature-induced electron spin catalysis.

[FeFe]-hydrogenases catalyze the reversible oxidation of H2 from electrons and protons at an organometallic active site cofactor named the H-cluster. In addition to the H-cluster, most [FeFe]-hydrogenases possess accessory FeS cluster (F-cluster) relays that function in mediating electron transfer with catalysis. There is significant variation in the structural properties of F-cluster relays among the [FeFe]-hydrogenases; however, it is unknown how this variation relates to the electronic and thermodynamic properties, and thus the electron transfer properties, of enzymes. Clostridium pasteurianum [FeFe]-hydrogenase II (CpII) exhibits a large catalytic bias for H2 oxidation (compared to H2 production), making it a notable system for examining if F-cluster properties contribute to the overall function and efficiency of the enzyme. By applying a combination of multifrequency and potentiometric electron paramagnetic resonance, we resolved two electron paramagnetic resonance signals with distinct power- and temperature-dependent properties at g = 2.058 1.931 1.891 (F2.058) and g = 2.061 1.920 1.887 (F2.061), with assigned midpoint potentials of −140 ± 18 mV and −406 ± 12 mV versus normal hydrogen electrode, respectively. Spectral analysis revealed features consistent with spin-spin coupling between the two [4Fe-4S] F-clusters, and possible functional models are discussed that account for the contribution of coupling to the electron transfer landscape. The results signify the interplay of electronic coupling and free energy properties and parameters of the FeS clusters to the electron transfer mechanism through the relay and provide new insight as to how relays functionally complement the catalytic directionality of active sites to achieve highly efficient catalysis.

A time-resolved electron paramagnetic resonance (TREPR) method with 40 ns time resolution and a high sensitivity suitable for the detection of short-lived radicals under thermal equilibrium is developed. The key is the introduction of a new detection technique named ultrawide single sideband phase sensitive detection (U-PSD) to the conventional continuous-wave EPR, which remarkably enhanced the sensitivity for the detection of broadband transient signals compared with the direct detection protocol. By repeatedly triggering a transient kinetic event f(t) (e.g., by laser flash photolysis) under a 100 kHz magnetic field modulation with precise phase control, this technique can build an ultrawide single sideband modulated signal. After single sideband demodulation, the flicker noise-suppressed signal f(t) with wide bandwidth is recovered. A U-PSD TREPR spectrometer prototype has been built, which integrated timing sequence control, laser flash excitation, data acquisition systems, and the U-PSD algorithm with a conventional continuous-wave EPR. It exhibited excellent performance in monitoring a model transient radical system, laser flash photolysis of benzophenone in isopropanol. Both the intense chemically induced dynamic electron polarization signals and the much weaker thermal equilibrium EPR signals of the generated acetone ketyl radical and benzophenone ketyl radical were clearly observed within a wide timescale ranging from sub-microsecond to milliseconds. This prototype validated the feasibility of the U-PSD technique and demonstrated its superior performance in studying complex photochemical systems containing various transient radicals, which complements the established TREPR techniques and provides a powerful tool for deep mechanistic understandings, such as in photoredox catalysis and artificial photosynthesis.

Cytochrome c peroxidases (bCcPs) are diheme enzymes required for the reduction of H2O2 to water in bacteria. There are two classes of bCcPs: one is active in the diferric form (constitutively active), and the other requires the reduction of the high-potential heme (H-heme) before catalysis commences (reductively activated) at the low-potential heme (L-heme). To improve our understanding of the mechanisms and heme electronic structures of these different bCcPs, a constitutively active bCcP from Nitrosomonas europaea ( NeCcP) and a reductively activated bCcP from Shewanella oneidensis ( SoCcP) were characterized in both the diferric and semireduced states by electron paramagnetic resonance (EPR), resonance Raman (rRaman), and magnetic circular dichroism (MCD) spectroscopy. In contrast to some previous crystallographic studies, EPR and rRaman spectra do not indicate the presence of significant amounts of a five-coordinate, high-spin ferric heme in NeCcP or SoCcP in either the diferric or semireduced state in solution. This observation points toward a mechanism of activation in which the active site L-heme is not in a static, five-coordinate state but where the activation is more subtle and likely involves formation of a six-coordinate hydroxo complex, which could then react with hydrogen peroxide in an acid-base-type reaction to create Compound 0, the ferric hydroperoxo complex. This mechanism lies in stark contrast to the diheme enzyme MauG that exhibits a static, five-coordinate open heme site at the peroxidatic heme and that forms a more stable FeIV═O intermediate.

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Inorganic pyrophosphatase (PPase) catalyses the hydrolysis reaction of inorganic pyrophosphate to phosphates. Our previous studies showed that manganese (Mn) activated PPase from the psychrophilic bacterium Shewanella sp. AS-11 (Mn-Sh-PPase) has a characteristic temperature dependence of the activity with an optimum at 5 °C. Here we report the X-ray crystallography and electron paramagnetic resonance (EPR) spectroscopy structural analyses of Sh-PPase in the absence and presence of substrate analogues. We successfully determined the crystal structure of Mn-Sh-PPase without substrate and Mg-activated Sh-PPase (Mg-Sh-PPase) complexed with substrate analogue (imidodiphosphate; PNP). Crystallographic studies revealed a bridged water placed at a distance from the di-Mn centre in Mn-Sh-PPase without substrate. The water came closer to the metal centre when PNP bound. EPR analysis of Mn-Sh-PPase without substrate revealed considerably weak exchange coupling, whose magnitude was increased by binding of substrate analogues. The data indicate that the bridged molecule has weak bonds with the di-Mn centre, which suggests a ‘loose’ structure, whereas it comes closer to di-Mn centre by substrate binding, which suggests a ‘well-tuned’ structure for catalysis. Thus, we propose that Sh-PPase can rearrange the active site and that the ‘loose’ structure plays an important role in the cold adaptation mechanism.

The catalytic conversion of N2O over Fe-exchanged zeolites is an essential process for controlling its anthropogenic emissions and detrimental environmental impact. In the present study, we monitored an industrial Fe–ferrierite catalyst under conditions of CO-assisted decomposition of N2O using operando electron paramagnetic resonance (EPR) spectroscopy within the modulated excitation (ME) paradigm. Exploiting this approach, we demonstrated that N2O decomposition occurs via reversible FeII/FeIII transitions localized exclusively on isolated FeII centers located in the β-cationic position, successfully distinguished among various spectator species. The temporal evolution of the reversible β-FeII/FeIII transitions under oxidizing and reducing atmospheres was determined with multivariate curve resolution (MCR) and via double integration of their EPR signal, allowing us to calculate the apparent activation energies for the oxidation and reduction half-cycles. Despite the reaction is controlled by the reduction half-cycle, i.e. N2O promotes full oxidation of the active β-FeII centres irrespective of temperature, the kinetic results indicate that temperature enhances the rate of this oxidation reaction more than the rate of reduction in CO-rich conditions. This study shows that quantitative and qualitative reaction monitoring at sub-minute temporal resolution via operando EPR spectroscopy is possible and sufficient signal-to-noise can be obtained if the experiments are performed according to the ME approach and if phase-sensitive detection (PSD) is employed. Furthermore, our results also indicate that analytical methods, such as MCR, can produce reliable results in the framework of time-resolved EPR spectroscopy.

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Current strategies for developing peroxidase-mimicking nanozymes seldom address the interplay between Fenton-type hemolytic and Poulos-Kraut heterolytic mechanisms in H2O2 activation. To reveal the active centers, reaction intermediates, and dynamic structural transformations during catalysis, we investigated Fe-doped TiO2 (Fe-TiO2) nanozymes that exhibit a dual-mechanism pathway. Operando ambient-pressure electron spin resonance spectroscopy and Raman measurements revealed that H2O2 molecules adsorb onto Fe-TiO2 surfaces, occupying oxygen vacancy sites (Ti-Ov-Ti) and forming peroxy bonds with Ti atoms (Ti-OOH). The incorporation of Fe facilitates both Fenton-type homolytic cleavage and Poulos-Kraut heterolytic cleavage of H2O2, enhancing peroxidase-like activity through interactions between substrates and Ti-OOH intermediates. The inhibitory effect of l-cysteine on the activity of Fe-TiO2 nanozymes inspired a rapid and selective l-cysteine biosensor. This study reveals that defect engineering introduces the Poulos-Kraut mechanism into peroxidase-mimicking nanozymes as an innovative alternative to the Fenton-type mechanism, offering a promising approach for exploring dual H2O2 activation pathways mimicking natural peroxidases.

The ‘power-to-hydrogen’ strategy aims at splitting water into O2 and H2 via the oxygen and hydrogen evolution reactions. The complex four-step oxygen evolution reaction (OER) limits the overall efficiency of hydrogen production. An important reason of the low efficiency is that the production of ground-state (triplet) O2 is a spin-forbidden reaction: in fact, the reactants, OH- or H2O, are diamagnetic, but the final product, O2, is a paramagnetic molecule. Recently, this was well-recognized theoretically1 and the use of spin selective catalysts was described as a possible way to promote the OER.2 . However, it remains complex to understand and exploit intrinsic and extrinsic magnetic features to enhance catalytic performance. Here, we investigate the role of magnetic moments in individual active sites in the catalyst surface layer and the role of spin order in ferromagnetic vs. paramagnetic catalysts, focussing on perovskite oxides. First, we investigated the role of Ni magnetic moment in the the (001), (110) and (111) facet of LaNiO3 electrocatalysts, which we studied using electrochemical measurements, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT+U) calculations.3 The results show a facet-dependent activity, where the (111) overpotential is ~60 mV lower as compared to the other facets. Closer investigation of the (001) and (111) facets reveals a surface transformation to a oxyhydroxide-like NiOO with edge-sharing octahedra,4 and we observed that the transformed surface is thicker for (111) than for (001).3 The detailed DFT+U analysis reveals important distinctions that give rise to the increased activity: the transformed LaNiO3 (111) surface exhibits a better match to the underlying perovskite layer. Moreover, protonation induces reduced Ni3+ with a finite magnetic moment. A moderate Jahn-Teller distortion enables a favorable binding of reaction intermediates. In contrast, the structural mismatch to the underlying LaNiO3(001)-substrate leads to a strong distortion of the transformed layer for this orientation and a weak binding of *O and ultimately to a different potential determining step (PDS), *OH→*O, compared to *O→*OOH for the transformed LaNiO3(111) surface. Second, we experimentally demonstrate the effect of intrinsic magnetic order on the OER on catalytic performance. Thin films of La0.67Sr0.33MnO3 grown by pulsed laser deposition with appropriate magnetic and electronic properties were chosen as well-defined model systems. Using the ferromagnetic to paramagnetic transition at the Curie temperature in these ferromagnetic perovskite oxides, the magnetic order of the catalysts were switched in situ during the OER by changing the temperature. For ferromagnetic films, the decrease in current density with decreasing temperature, induced by the reduction of thermal energy, was suppressed for temperatures below the Curie temperature, indicating that the presence of ferromagnetic ordering below Curie temperature enhances OER activity. This claim is further supported by an enhancement of OER activity for the same ferromagnetic film upon alignment of magnetic domains with an external magnetic field. All in all, our results reveal that the spin state, intrinsic spin order, and extrinsic magnetic fields are decisive for the OER activity. Biz, C., Fianchini, M. & Gracia, J. Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange. ACS Catal 11, 14249–14261 (2021). Sun, Y. et al. Spin‐Related Electron Transfer and Orbital Interactions in Oxygen Electrocatalysis. Advanced Materials 32, 2003297 (2020). Füngerlings, A. et al. Crystal-facet-dependent surface transformation dictates the oxygen evolution reaction activity in lanthanum nickelate. in preparation (2023). Baeumer, C. et al. Tuning electrochemically driven surface transformation in atomically flat LaNiO3 thin films for enhanced water electrolysis. Nat Mater 20, 674–682 (2021).

Single-atom Fe–N–C catalysts have demonstrated promising potential in the oxygen reduction reaction (ORR), yet their intrinsic activity remains less than ideal. Orbital hybridization provides a versatile means to modulate the thermodynamic and kinetic properties during electrochemical processes. In this study, we adopt an “axial ligand boron-modulation” strategy to regulate the electronic structure of single-atom Fe sites through d–p orbital hybridization. The synthesized FeN4–B/NC demonstrates exceptional ORR activity with a half-wave potential of 0.915 V, surpassing planar FeN4/NC and commercial Pt/C. In situ XAS results reveal the dynamic stretching of Fe–N/O and Fe–B bonds during the ORR process, providing an intuitive confirmation that the single-atom sites undergo reversible structural changes to optimize the adsorption of reaction intermediates. Theoretical investigations combined with zero-field cooling temperature dependence analyses demonstrate that in the intermediate spin state, hybridization occurs between the central Fe's 3d orbitals and B's 2p orbitals, which results in increased eg orbital occupancy and positions the d-band center closer to the Fermi level, which enhances charge transfer efficiency and O2 adsorption capabilities. Furthermore, the newly developed FeN4–B/NC catalyst shows remarkable performance in liquid and quasi-solid-state zinc–air batteries.

We provide the rational design of dual atom catalysts (DACs) supported on nitrogen-doped graphene for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through high-throughput computational screening of M 1 M 2 N6-DAC systems, where M 1 and M 2 represent Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt metals. We predict that FeRuN6-DAC at the summit of the volcano plot exhibits a low theoretical ORR overpotential ( η ORR ) of 0.24 V and a low theoretical OER overpotential ( η OER ) of 0.19 V. The low η ORR and η OER result from the catalytic performance of the Fe site being tuned to electronic properties that facilitate adsorption and desorption of the OH* intermediate. Inspired by these hybrid density functional theory (DFT) computational and machine learning (ML) results, we synthesized FeRuN6-DAC, FeN4-SAC, and RuN4-SAC and characterized them using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and in-situ electron spin resonance (ESR). Our in-situ ESR spectroscopy signifies that the spin of the Fe active site increases with increasing applied potential due to the increase in the concentration of OH* intermediate on Fe. We verified experimentally the predicted catalytic performances, finding that FeRuN6-DAC leads to an experimental ORR overpotential of 0.29 V with a Tafel slope of 104 mVdec (cid:0) 1 and an OER over-potential of 0.27 V with a Tafel slope of 124 mVdec (cid:0) 1 . The rechargeable Zinc-air battery setup was fabricated with FeRuN6-DAC in place of the cathode, showing a maximum power density of 0.45 W/cm 2 at the current density of 0.44 A/cm 2 and good stability after 120 cycles. According to our findings, we demonstrate that DFT-guided strategies are useful for designing advanced DACs applicable to ORR, OER, and Zinc-air battery applications.

No abstract available

The chiral-induced spin selectivity effect (CISS) is a breakthrough phenomenon that has revolutionized the field of electrocatalysis. We report the first study on the electron spin-dependent electrocatalysis for the oxygen reduction reaction, ORR, using iron phthalocyanine, FePc, a well-known molecular catalyst for this reaction. The FePc complex belongs to the non-precious catalysts group, whose active site, FeN4, emulates catalytic centers of biocatalysts such as Cytochrome C. This study presents an experimental platform involving FePc self-assembled to a gold electrode surface using chiral peptides (L and D enantiomers), i.e., chiro-self-assembled FePc systems (CSAFePc). The chiral peptides behave as spin filters axial ligands of the FePc. One of the main findings is that the peptides' handedness and length in CSAFePc can optimize the kinetics and thermodynamic factors governing ORR. Moreover, the D-enantiomer promotes the highest electrocatalytic activity of FePc for ORR, shifting the onset potential up to 1.01 V vs. RHE in an alkaline medium, a potential close to the reversible potential of the O2/H2O couple. Therefore, this work has exciting implications for developing highly efficient and bioinspired catalysts, considering that, in biological organisms, biocatalysts that promote O2 reduction to water comprise L-enantiomers.

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No abstract available

The role of electronic spin in electrocatalysis has led to the emerging field of “spin-dependent electrocatalysis”. While spin effects in individual active sites have been well understood, spin coupling among multiple sites remains underexplored in electrocatalysis, which will bring forth new active sites and mechanisms. In this work, we propose a general theory to understand the spin coupling in electrocatalysis. Inspired by spintronics, the energy of the spin-polarized bond of catalyst–adsorbate can be effectively tuned by exchange splitting, resulting in a spin-dependent mechanism. To validate this hypothesis, we take the Fe2N6 dual-atom-catalyst (DAC) with parallel and antiparallel spin (PS/APS) alignments as an example. Our calculation demonstrates that spin exchange splitting significantly determines the ORR mechanism, leading to a huge discrepancy in ORR activity in APS-Fe2N6 (UL = 1.04 V vs. SHE) and PS-Fe2N6 (UL = 0.67 V vs. SHE). We further reveal that PS alignment enhances exchange splitting and strengthens OH/O2 adsorption, while APS alignment reduces exchange splitting and weakens OH/O2 adsorption. This mechanism is further validated with other bi-metallic DACs. Our work first unravels how spin exchange splitting alters the catalytic activity and mechanism, offering significant mechanistic insights into spin-related electrocatalysis.

Controlling the electron spin of oxygen-containing intermediates is crucial for efficient oxygen electrocatalysis toward clean energy technologies such as fuel cells and water electrolysis. Current strategies for controlling the electron spins rely mainly on tuning the chemical structure of the oxygen electrocatalyst, which is often hardly achieved for metal and oxide electrocatalysts. The chiral-induced spin selectivity (CISS) effect, a significant discovery in chiral spintronics, represents an alternative approach for tuning the spin selectivity of oxygen electrocatalysts. Here we demonstrate the use of intrinsic chiral nanoparticles as electron-spin filters to tune the selectivity in oxygen electrocatalytic reactions. Chiral Au nanoparticles with a concave vortex cube structure were employed as the chiral substrate, exhibiting highly tunable optical chirality and intriguing CISS-like effect. As model systems, the catalytically active components such as Pt or Ni(OH)2 are overgrown onto chiral Au nanoparticles to construct the chiral hybrid electrocatalysts. Remarkably, both cases show chirality-dependent tunable activities over oxygen reduction/evolution reactions, respectively. The insights gained from this work not only shed light on the underlying mechanisms dictating the CISS-enhanced oxygen electrocatalysis by chiral nanoparticles but also provide an important knowledge framework that guides the rational design of chiral electrocatalysts toward oxygen electrocatalysis.

Electrochemical nitrate reduction to ammonia offers environmental and energy benefits, but progress is hindered by sluggish multistep proton‐coupled electron transfers and competing side reactions. Here, we introduce an antiperovskite CuNCo3 catalyst featuring a 3d–3d interaction framework. This framework stabilizes spin‐selective Co sites even upon surface Co‐N bond cleavage and drives asymmetric nitrate consumption. CuNCo3 achieves 100% Faradaic efficiency and an NH3 production rate of 124.6 mg mgcat−1 h−1 at −0.4 V vs. RHE. Operando XAS, XES, and ATR‐FTIR directly link the evolution of spin‐selective Co sites with specific NO3RR intermediates, revealing that spin‐selective Co sites lower hydrogenation barriers and accelerate key steps. These results demonstrate that spin‐selective anti‐perovskite frameworks provide a robust, earth‐abundant platform for high‐performance nitrate‐to‐ammonia electrocatalysts.

Promoting the initially deficient but economical catalysts to high-performing competitors is important for developing superior catalysts. Unlike traditional nano-morphology construction methods, this work focuses on intrinsic catalytic activity enhancement via heteroatom doping strategies to induce lattice distortion and optimize spin-dependent orbital interaction to alter charge transfer between catalysts and reactants. Experimentally, a series of different concentrations of fluorine-doped lanthanum cobaltate (Fx -LaCoO3 ) exhibiting excellent electrocatalytic activity is synthesized, including a low overpotential of 390 mV at j = 10 mA cm-2 for OER and a large half-wave potential of 0.68 V for ORR. Meanwhile, the assembled rechargeable Zn-air batteries deliver an excellent performance with a large specific capacity of 811 mAh/gZn under 10 mA cm-2 and stability of charge/recharge (120 h). Theoretically, taking advantage of density functional theory calculations, it is found that the prominent OER/ORR performance arises from the spin state transition of Co3+ (Low spin state (LS, t2g 6 eg 0 ) → Intermediate spin state (IS, t2g 5 eg 1 ) and the mediated d-band center upshift by F atom incorporation. This work establishes a novel avenue for designing superior electrocatalysts in perovskite-based oxides by regulating spin states.

Anodic oxygen evolution reaction (OER) that involves a spin-dependent singlet-to-triplet oxygen changeover largely restrains the water electrolysis efficiency for hydrogen production. However, the modulation of spin state is still challengeable for most OER catalysts, and there remains a debate on deciphering the active spin state in OER. Here, we pioneered an asymmetric Fe-incorporated NiPS3 tactic system to retune the metal localized spin for efficient OER electrocatalysis. It is unraveled that the synergistic effect of medium-spin FeIII site and P/S coordination can effectively boost OER activity and Cl resistance selectivity in alkaline/sea water. Resultantly, the Fe/NiPS3-based asymmetric electrodes exhibit low cell voltages of 1.50 volts/1.52 volts in alkaline/sea water at 10 milliamperes per square centimeter, together with a sustainable retention for 1000 hours. It also delivers the durable performance in anion exchange membrane water electrolyzers with a low operation voltage at 45°C. This research navigates the atomic localized spin state as the criterion in rationalizing efficient nonprecious alkaline/sea water oxidation electrocatalysts.

While the catalytic enhancement effect of magnetic fields in electrocatalytic water splitting has been established, the underlying mechanisms and optimal application strategies remain poorly understood. Here, we present a comprehensive investigation of the effects of a magnetic field on electrocatalysis using engineered Co-Ru@RuO2 ferrimagnetic materials, elucidating the complex relationships among magnetic fields, spin coupling, and catalytic activity in both oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Our systematic study reveals a threshold-dependent response: weak magnetic fields (<1 T) have a negligible impact under electrochemical steady-state conditions, whereas strong magnetic fields (>3 T) significantly alter the steady state and enhance the catalytic performance. We introduce the novel concept of temporal–spatial enabling, demonstrating that the precisely timed application of magnetic fields particularly prior to electrochemical reactions can significantly enhance catalytic efficiency in both the OER and HER. Through innovative quasi-in situ temperature-dependent magnetization measurements, we provide direct evidence that magnetic fields modulate the electronic spin structure of the catalyst, resulting in improved catalytic activity. These findings not only deepen our fundamental understanding of magnetic field effects in electrocatalysis but also establish a new paradigm for optimizing catalytic performance via strategic manipulation of magnetic fields and spin dynamics, opening promising avenues for next-generation energy conversion technologies.

The chiral‐induced spin selectivity effect enables the application of chiral organic materials for spintronics and spin‐dependent electrochemical applications. It is demonstrated on various chiral monolayers, in which their conversion efficiency is limited. On the other hand, relatively high spin polarization (SP) is observed on bulk chiral materials; however, their poor electronic conductivities limit their application. Here, the design of chiral MoS2 with a high SP and high conductivity is reported. Chirality is introduced to the MoS2 layers through the intercalation of methylbenzylamine molecules. This design approach activates multiple tunneling channels in the chiral layers, which results in an SP as high as 75%. Furthermore, the spin selectivity suppresses the production of H2O2 by‐product and promotes the formation of ground state O2 molecules during the oxygen evolution reaction. These potentially improve the catalytic activity of chiral MoS2. The synergistic effect is demonstrated as an interplay of the high SP and the high catalytic activity of the MoS2 layer on the performance of the chiral MoS2 for spin‐dependent electrocatalysis. This novel approach employed here paves way for the development of other novel chiral systems for spintronics and spin‐dependent electrochemical applications.

Regulating the electron-spin state of metal active sites is a rarely cultivated topic for oxygen electrocatalysis. Here, a dual-ligand metal-organic framework (DM) is developed to endow Co sites with D4h crystal symmetry, reconfiguring their orbital degeneracy and electron spin state. The discretized spin-orbital configuration offers the accelerated transformation of the O-related intermediate by accepting electrons via partial d-orbital occupation and mediation of the hydroxyl adsorption strength through electron donation to O p-orbitals. With this orbital flexibility, Co sites serve as "Lewis acid-base" pairs that hasten O redox of oxygen during Zn-air battery cycling, which is validated by operando X-ray absorption spectroscopy and theoretical modeling. Compared to counterparts with different crystal symmetries, Zn-air batteries using the DM electrocatalyst showcase reduced charge-discharge voltage gap and high round-trip energy efficiency at high areal capacity.

Water electrolysis, driven by renewable electricity, offers a sustainable path for hydrogen production. However, efficient bifunctional electrocatalysts are needed to overcome the high overpotentials of both the oxygen evolution reaction and hydrogen evolution reaction. To address this, a novel catalyst system is developed integrating plasmonic nanoreactors with chirality‐induced spin selectivity. In this system, chiral Au nanoparticles act as antennae, while single‐atom iridium serves as the catalytic reactor, achieving a 3.5 fold increase in reaction kinetics (at 1.57 V vs RHE) compared to commercial IrO2 catalysts and enhancing durability by over 4.8 times relative to conventional Pt/C || IrO2 systems. Density functional theory and operando X‐ray absorption spectroscopy reveal that plasmon‐driven spin alignment polarizes the Ir atom, significantly enhancing stability (>480 h at 100 mA cm−2) under acidic conditions. This work represents a major advance in spin polarization for plasmonic electrocatalysis, offering a new route to sustainable energy solutions.

Efficient and durable oxygen evolution reaction (OER) electrocatalysis is essential for advancing sustainable seawater electrolysis. In this work, a high-performance Ni–Fe–Mn–Ce medium-entropy oxyhydroxide is constructed via in situ electrochemical reconstruction strategy for the OER. Guided by density functional theory (DFT), the effects of eight candidate fourth-metal elements (Al, Ce, Co, Cr, Cu, Sn, Zn, or Zr) on the electronic structure and reaction energetics of the NiFeMn(O)OH matrix are comprehensively investigated, revealing the unique advantages of Ce in optimizing intermediate adsorption energies and lowering the theoretical overpotential. The catalyst requires an overpotential of only 183 mV at 10 mA cm−2 in 1 M KOH, while maintaining a low overpotential of 224 mV in alkaline seawater, along with excellent resistance to Cl− corrosion. Operando spectroscopic characterizations reveal dynamic valence evolution and charge redistribution among Ni4+, Fe3+, and Ce3+/Mn2+ species, which contribute to stabilizing intermediate adsorption and promoting electron transfer. Further electronic structure analysis demonstrates a favorable d-band center near the Fermi level and pronounces spin polarization in the medium-entropy system, which synergistically enhance OER kinetics. This work highlights the potential of entropy engineering combined with theoretical guidance in the development of advanced multi-metallic electrocatalysts for efficient seawater splitting.

Electrolytic hydrogen is identified as a crucial component in the desired decarbonisation of the chemical industry, utilizing renewable energy to split water into hydrogen and oxygen. Water electrolysis still requires important scientific advances to improve its performance and lower its costs. One of the bottlenecks in this direction is related to the sluggish anodic oxygen evolution reaction (OER). Producing anodes with competitive performance remains challenging due to the high energy losses and the harsh working conditions typically required by this complex oxidation process. Recent advancements point to spin polarization as an opportunity to enhance the kinetics of this spin-restricted reaction, yielding the paramagnetic O2 molecule. One powerful strategy deals with the generation of chiral catalytic surfaces, typically by surface functionalisation with chiral organic molecules, to promote the chiral-induced spin selectivity (CISS) effect during electron transfer. However, the relationship between optical activity and enhanced electrocatalysis has been established only from indirect experimental evidence. In this work, we have exploited operando electrochemical and spectroscopic tools to confirm the direct relationship between the faster OER kinetics and the optical activity of enantiopure Fe–Ni metal oxides when compared with that of achiral catalysts in alkaline conditions. Our results show the participation of chiral species as reactive intermediates during the electrocatalytic reaction, supporting the appearance of a mechanistic CISS enhancement. Furthermore, these intrinsically chiral transition-metal oxides maintain their enhanced activity in full cell electrolyser architectures at industrially relevant current densities.

Two-dimensional (2D) topological materials have emerged as promising candidates for electrocatalysis owing to their exotic surface electronic structures governed by spin–orbit coupling (SOC). However, under realistic electrochemical conditions, these surface electronic properties can be significantly adjusted by the dynamic reconstruction of catalyst surfaces, referred to as electrochemical surface states (ESSs), which remains underexplored in the context of topological materials. Here, using monolayer PtBi2 as a model catalyst, we reveal that the SOC-enabled topological surface states (TSSs) of PtBi2 can be actively modulated by ESSs even without inducing structural phase transitions. Through density functional theory computations, we identify that ∼1 monolayer (ML) of HO* adsorbates dominates the surface under oxygen reduction reaction (ORR) conditions, inducing localized SOC-enabled states and a flat band with high density near the Fermi level. This reconstructed TSS landscape improves orbital coupling with oxygen intermediates and reduces the electrostatic dipole sensitivity, leading to optimal adsorption energetics for the ORR. pH-dependent microkinetic simulations further confirm that this interplay drives the system to near-peak ORR activity. Extension study to other redox-relevant ESSs (e.g., H*- and O*-covered surfaces) and different 2D topological materials, like PdBi2 and MoTe2, highlights the broader relevance of this mechanism. This study establishes a mechanistic framework linking ESSs and TSSs in 2D topological materials, emphasizing that the associated SOC effects are crucial and that they should not be dismissed in related electrocatalyst design.

Despite decades of intensive study, the mechanism of many electrocatalytic reactions involving reactive oxygen species (ROS) such as the oxygen reduction reaction (ORR) remain poorly understood due to their complex, multistep, and interface-dependent nature. Computational studies generally suggest that the stabilization of various adsorbed radical intermediates such as hydroxyl (OH • ), hydroperoxyl (OOH • ), or oxygen atoms (O • ) is key to enhancing the kinetics of ORR. 1 Despite a clear computational picture of the importance of these species, their direct experimental detection and quantification, particularly under reaction conditions, remain rare in the literature. Here, we have used a novel strategy based on redox-active spin traps as a method to identify and quantify these reactive oxygen intermediates in situ . 2,3,4 Typically, spin traps molecules to trap and stabilize short-lived radical species for detection ex situ using electron spin resonance (ESR). However, the use of a redox active spin trap allows for the application of electrochemical methods to investigate these processes. Scanning electrochemical microscopy (SECM) is an ideal technique to measure the generation of the resulting redox-active spin trapped adducts because it allows for the sensitive local detection and quantification of dilute quantities of species in real-time. 5 This allows for the design of in situ experiments that can measure and quantify with high spatial and temporal resolution. We have validated this technique during the generation hydroxyl radicals on boron-doped diamond, 2 during the corrosion of lead-acid battery cathodes 3 and during the ORR at Fe-N-C electrocatalysts. 4 In this talk, we will focus on the expansion of our methodologies to discern on the generation of ROS discharged in solution vs those remaining adsorbed on the electrode. Furthermore, the use of a variety of spin trapping molecules dedicated to different ROS intermediates will be highlighted. Our new technique provides unprecedented insight into the quantity and identity of ROS formed at a variety of electrochemical interfaces, offering new evidence for the formation of both main and minority products in operando. w. [1] Norskov, J.K. et al. J. Phys. Chem. B , 2004 , 108, 46, 17886–17892. DOI: 10.1021/jp047349j. [2] Barroso-Martinez, J. et al. J. Am. Chem. Soc ., 2022 , 144, 41, 18896–18907. DOI: 10.1021/jacs.2c06278. [3] Asserghine, A. et al. Chem. Sci ., 2023 , 14, 12292-12298. DOI: 10.1039/d3sc04736a. [4] Putnam. S.T., et al. Chem. Sci., 2024 , 15, 10036-10045. DOI: 10.1039/d4sc01553c. [5] Putnam, S.T., et al. Anal. Chem ., 2025, DOI: 10.1021/acs.analchem.4c06996.

The ability to determine the electronic structure of catalysts during electrochemical reactions is highly important for identification of the active sites and the reaction mechanism. Here we successfully applied soft X-ray spectroscopy to follow in operando the valence and spin state of the Co ions in Li 2 Co 2 O 4 under oxygen evolution reaction (OER) conditions. We have observed that a substantial fraction of the Co ions undergo a voltage-dependent and time-dependent valence state transition from Co 3+ to Co 4+ accompanied by spontaneous delithiation, whereas the edge-shared Co–O network and spin state of the Co ions remain unchanged. Density functional theory calculations indicate that the highly oxidized Co 4+ site, rather than the Co 3+ site or the oxygen vacancy site, is mainly responsible for the high OER activity. Determining catalyst electronic structures during electrochemical reactions is crucial to understand mechanisms. Here authors perform in operando soft X-ray spectroscopy on a cobalt oxide catalyst during O 2 evolution and observe voltage and time-dependent valence state transitions.

Oxygen evolution reaction (OER) plays a determining role in electrochemical energy conversion devices, but challenges remain due to the lack of effective low-cost electrocatalysts and insufficient understanding about sluggish reaction kinetics. Distinguish from complex nano-structuring, this work focuses on the spin-related charge transfer and orbital interaction between catalysts and intermediates to accelerate catalytic reaction kinetics. Herein, we propose a simple magnetic-stimulation approach to rearrange spin electron occupation in noble-metal-free metal-organic frameworks (MOFs) with a feature of thermal-differentiated superlattice, in which the localized magnetic heating in periodic spatial distribution makes the spin flip occur at particular active sites, demonstrating a spin-dependent reaction pathway. As a result, the spin-rearranged Co0.8Mn0.2 MOF displays mass activities of 3514.7 A gmetal−1 with an overpotential of ~0.27 V, which is 21.1 times that of pristine MOF. Our findings provide a new paradigm for designing spin electrocatalysis and steering reaction kinetics. The oxygen evolution reaction in magnetic catalysts is related with their spin configuration. Here, the authors propose a magnetic-stimulation method to rearrange spin electron occupation in thermal-differentiated superlattices.

In situ monitoring is essential for catalytic process design, offering real‐time insights into active structures and reactive intermediates. Electron paramagnetic resonance (EPR) spectroscopy excels at probing geometric and electronic properties of paramagnetic species during reactions. Yet, state‐of‐the‐art liquid‐phase EPR methods, like flat cells, require custom resonators, consume large amounts of reagents, and are unsuited for tracking initial kinetics or use with solid catalysts. To overcome these limitations, a droplet‐based microfluidics platform is introduced for real‐time EPR monitoring of liquid‐phase catalytic reactions. By encapsulating solid and dissolved species within nanoliter droplets, this approach enables precise control over mass transport, reduces reagent consumption, and maintains uniform residence times irrespective of acquisition duration, permitting precise analysis of each spectral component under identical conditions. The platform's compatibility with standard resonators facilitates straightforward integration into any EPR spectrometer. Its versatility is demonstrated by monitoring dynamic ligand exchange processes, key for activating homogeneous catalysts, and tracking redox and radical kinetics in ascorbic acid oxidation by Cu(II) catalysts. Importantly, this method captures both supported and dissolved transition metal species, offering comprehensive insights into catalyst deactivation via metal leaching. This microfluidic approach sets a new standard for liquid‐phase in situ EPR measurements, advancing studies of homogeneous and heterogeneous catalytic systems.

No abstract available

Development of sustainable catalysts for synthetic transformations is one of the most challenging and demanding goals. The high prices of precious metals and the unavoidable leaching of toxic metal species leading to environmental contamination make the transition metal-free catalytic systems especially important. Here we demonstrate that carbene active centers localized on carbon atoms at the zigzag edge of graphene represent an alternative platform for efficient catalytic carbon-carbon bond formation in the synthesis of benzene. The studied acetylene trimerization reaction is an efficient atom-economic route to build an aromatic ring-a step ubiquitously important in organic synthesis and industrial applications. Computational modeling of the reaction mechanism reveals a principal role of the reversible spin density oscillations that govern the overall catalytic cycle, facilitate the product formation, and regenerate the catalytically active centers. Dynamic π-electron interactions in 2D carbon systems open new opportunities in the field of carbocatalysis, unachievable by means of transition metal-catalyzed transformations. The theoretical findings are confirmed experimentally by generating key moieties of the carbon catalyst and performing the acetylene conversion to benzene.

The magnetic interactions between the spin of an unpaired electron and the surrounding nuclear spins can be exploited to gain structural information, to reduce nuclear relaxation times as well as to create nuclear hyperpolarization via dynamic nuclear polarization (DNP). A central aspect that determines how these interactions manifest from the point of view of NMR is the timescale of the fluctuations of the magnetic moment of the electron spins. These fluctuations, however, are elusive, particularly when electron relaxation times are short or interactions among electronic spins are strong. Here we map the fluctuations by analyzing the ratio between longitudinal and transverse nuclear relaxation times T1/T2, a quantity which depends uniquely on the rate of the electron fluctuations and the Larmor frequency of the involved nuclei. This analysis enables rationalizing the evolution of NMR lineshapes, signal quenching as well as DNP enhancements as a function of the concentration of the paramagnetic species and the temperature, demonstrated here for LiMg1-xMnxPO4 and Fe(III) doped Li4Ti5O12, respectively. For the latter, we observe a linear dependence of the DNP enhancement and the electron relaxation time within a temperature range between 100 and 300 K.

An efficient catalytic system for nitrogen (N2) photofixation generally consists of light-harvesting units, active sites, and an electron-transfer bridge. In order to track photogenerated electron flow between different functional units, it is highly desired to develop in situ characterization techniques with element-specific capability, surface sensitivity, and detection of unoccupied states. In this work, we developed in situ synchrotron radiation soft X-ray absorption spectroscopy (in situ sXAS) to probe the variation of electronic structure for a reaction system during N2 photoreduction. Nickel single-atom and ceria nanoparticle comodified reduced graphene oxide (CeO2/Ni-G) was designed as a model catalyst. In situ sXAS directly reveals the dynamic interfacial charge transfer of photogenerated electrons under illumination and the consequent charge accumulation at the catalytic active sites for N2 activation. This work provides a powerful tool to monitor the electronic structure evolution of active sites under reaction conditions for photocatalysis and beyond.

Single-atom nanozymes (SANs) have attracted great attention in constructing devices for instant biosensing due to their excellent stability and atom utilization. Here, Mo atoms were immobilized in 2D nitrogen-doped carbon films by cascade-anchored one-pot pyrolysis to obtain Mo single-atom nanozyme (Mo-SAN) with high atomic loading (4.79 wt %) and peroxidase-like activity. The coordination environment and enzyme-like activity mechanism of Mo-SAN were studied by combining synchrotron radiation and density functional theory. The strong oxophilicity of single-atom Mo makes the catalytic center more capable of transferring electrons to free radicals to selectively generate •OH in the presence of H2O2. Choline oxidase and Mo-SAN were used as signal opening unit and signal amplification unit, respectively. Combining the portability and visualization functions of smartphone and test strips, a paper-based visual sensing platform was constructed, which can accurately identify choline at a concentration of 0.5-35 μM with a limit of detection as low as 0.12 μM. The recovery of human serum samples was 96.4-102.2%, with an error of less than 5%. Furthermore, the potential of Mo-SAN to efficiently generate toxic •OH in tumor cells was intuitively confirmed. This work provides a technical and theoretical basis for designing highly active SANs and detecting neurological markers.

Catalytic removal of NO and CO from exhaust is imperative due to their detrimental effects on the environment and human health, while the nature of active sites driving efficient NO reduction remains elusive. Herein, in combination with state-of-the-art mass spectrometry and quantum-chemical calculations, we demonstrate that copper-vanadium oxide clusters Cu3VO3-5- can catalytically reduce four NO molecules into N2O by CO. This finding represents a significant improvement in cluster science in which two NO molecules are commonly involved in the catalysis. The key to driving this substantially improved NO reduction efficiency by Cu3VO3- lies in the unique structure of intermediate product Cu3VO4-, which electronically resembles Cu3VO3- with a single unpaired electron localized in the V 3d orbital. This electronic configuration is vital to selectively reducing NO into N2O. Cu3VO3- can be regenerated through CO oxidation by product Cu3VO5- to complete the catalysis. The fundamental reasons behind this intriguing NO reduction behavior were further rationalized by theoretical calculations.

In this report, an o-phenylene-bridged tetradented redox-noninnocent bis-azopyridyl ligand [L] and its copper complexes [1] and [2] were synthesized and characterized. The electron transfer events of [L], as well as [1] and [2], were characterized by single-crystal X-ray structure determination, various spectroscopic studies, and DFT calculations. While [1] [[L]Cu(II)Cl2] has unreduced [L], [2], [[L]•-Cu(I)Cl] contains a one-electron-reduced ligand [L]•- , which is antiferromagnetically coupled with the unpaired spin on Cu(II). Reduction of [2] by one electron generated the complex [2]•-, which remained in an electronically bistable situation in the form of valence tautomers: [2A]•-, [[L]•-Cu(I)Cl]•- and [2B]•-, [[L]2-Cu(II)Cl]•-. Further one-electron reduction of [2]•- generated a mixture of Cu complexes: [2A]-, [[L]2-Cu(I)]- and [2B]-, [[L]3•-Cu(II)]-. Complexes [1] and [2] were examined for the catalytic oxidation of alcohols. The complex [2] was more efficient than [1]. The protocol was highly efficient and versatile with both primary as well as secondary aromatic and aliphatic alcohols. Mechanistic investigations showed that the complex [2] generated [[L]•-Cu(I)OCH2Ph]•- (A) as the active catalyst, which subsequently, through its ligand-based redox events, acted as the catalyst over the course of the reaction.

Radical scavenging reaction rate constants were measured by monitoring the free induction decay (FID) of the unpaired electron of radicals by using laser-synchronized pulsed-EPR. This method probes large electron spin magnetization arisen from dynamic electron spin polarization (DEP), which remarkably enhances the EPR signal. DEP decays with the longitudinal spin relaxation time, which was observed by using the FID detection method. In the presence of a radical scavenger, the DEP decay time depends on both spin-lattice relaxation and the chemical reaction with the scavenger, the latter of which reduces radical concentration. The plots of DEP decay rates against the radical scavenger concentrations gave the pseudo-first-order reaction rate constants for various radicals. This procedure was applied to determine the radical scavenging reaction rate constants of hydroxycyclohexyl, 2-hydroxypropyl, diphenylphosphinoyl, and α,α-dimethoxybenzyl radicals. The measured rate constants show good agreement with the previously reported values determined by using another method monitoring electron spin echo (ESE) decays of the radicals. We discussed the advantageous and disadvantageous characters of the FID detection method with respect to the existing ESE method in the viewpoints of signal intensity, selectivity of radicals, the simpleness of the measurements, and so on.

Catalytic ozonation technology is crucial for environmental remediation due to its exceptional efficiency and capability for complete mineralization of organic pollutants. However, hindered by spin-forbidden transitions, effective catalytic ozonation remains contingent upon the electronic properties and interfacial interactions of the catalyst. Recent studies identify interfacial atomic metal-oxygen species (M-*O) as a key descriptor in catalytic ozonation, determining the derivation of reactive species and subsequent reactivity. Herein, we modulated the high-spin localized Co active sites in HE-Co3O4 via a high-entropy strategy, which selectively stabilizes Co-*O surface species, thereby enhancing catalytic ozonation efficiency. HE-Co3O4 exhibits a 5-fold higher degradation rate than Co3O4 for 50 ppm CH3SH elimination (63-fold the mass activity compared to commercial MnO2) while maintaining exceptional stability over 24 h at 298 K. Electron paramagnetic resonance (EPR) and magnetization hysteresis (M-H) measurements confirm the transition of Co3+ to high-spin states in HE-Co3O4. Density functional theory (DFT) calculations reveal that unpaired electrons enhance the hybridization of Co 3d with O 2p orbitals, thereby establishing a Co-*O mediated interfacial pathway. This mechanism is directly observed through in situ Raman spectroscopy. These findings provide insights into the targeted modulation of catalyst electronic structures for ozone-catalyzed environmental remediation.

In this study, boron-doped porous carbon materials (BCs) with high surface areas were synthesized employing coffee grounds as carbon source and sodium bicarbonate and boric acid as precursors; afterward, nanoscale zero-valent iron (nZVI) and BCs composites (denoted as nZVI@BCs) were further prepared through reduction of FeSO4 by NaBH4 along with stirring. The performance of the nZVI@BCs for activating persulfate (PS) was evaluated for the degradation of bisphenol A (BPA). In comparison with nZVI@Cs/PS, nZVI@BCs/PS could greatly promote the degradation and mineralization of BPA via both radical and non-radical pathways. On the one hand, electron spin resonance and radical quenching studies represented that •OH, SO4•−, and O2•− were mainly produced in the nZVI@BCs/PS system for BPA degradation. On the other hand, the open circuit voltages of nZVI@BCs and nZVI@Cs in different systems indicated that non-radical pathway still existed in our system. PS could grab the unstable unpaired electron on nZVI@BCs to form a carbon material surface-confined complex ([nZVI@BCs]*) with a high redox potential, then accelerate BPA removal efficiency via direct electron transfer. Furthermore, the performances and mechanisms for BPA degradation were examined by PS activation with nZVI@BC composites at various conditions including dosages of nZVI@BCs, BPA and PS, initially pH value, temperature, common anions, and humid acid. Therefore, this study provides a novel insight for development of high-performance carbon catalysts toward environmental remediation.

Cu nanoclusters represent a type of atomically precise nanomaterial that exhibits excellent catalytic performance. So far, exploration of the structural chemistry and study of the electronic (e.g., dielectric property), magnetic, and mechanical properties of Cu nanoclusters still remain in the early stage. In this work, we report a Cu nanocluster, [Cu19(PPh3)4(PET)16] (PPh3 = triphenylphosphine; PET = 2-phenylethanethiol), which contains a special orthogonally packed triangular kernel with an unexpected three-valence-electron, open-shelled system. This result significantly differs from the polyhedral structures and the superatomic electronic configurations in previously reported Cu nanoclusters. The unpaired electrons in Cu19 lead to paramagnetism, which is confirmed by a superconducting quantum interference device (SQUID). Of note, the solution-assembled Cu19 crystal displays an unexpectedly high dielectric constant over a wide frequency range (∼75 at 1 kHz-1 MHz), which arises from the displacement of the valence electrons and the sharply increased dipole under the electric field. This performance exceeds that of most of the currently used solution-processable dielectric materials (e.g., polymers). Our work demonstrates the rich structural chemistry and the distinct electronic, magnetic, and mechanical properties of Cu nanoclusters and unveils their potential applications as high-performance, solution-processable dielectric materials.

The reaction of D-glucose oxidase (GOx) with D- and L-glucose was investigated using confocal fluorescence microscopy and Hall voltage, after the enzyme was adsorbed as a monolayer. By adsorbing the enzyme on a ferromagnetic substrate, we verified that the reaction is spin dependent. This conclusion was supported by monitoring the reaction when the enzyme is adsorbed on a Hall device that does not contain any magnetic elements. The spin dependence is consistent with the chiral-induced spin selectivity (CISS) effect; it can be explained by the improved fidelity of the electron transfer process through the chiral enzyme due to the coupling of the linear momentum of the electrons and their spin. Since the reaction studies often serve as a model system for enzymatic activity, the results may suggest the general importance of the spin-dependent electron transfer in bio-chemical processes.

By using state-of-the-art mass spectrometry and guided by the newly discovered single-electron mechanism (SEM; e.g., Ti3+ + 2NO → Ti4+-O•- + N2O), we determined experimentally that the vanadium-aluminum oxide clusters V4-xAlxO10-x- (x = 1-3) can catalyze the reduction of NO by CO and substantiated theoretically that the SEM still prevails in driving the catalysis. This finding marks an important step in cluster science in which a noble metal had been demonstrated to be indispensable in NO activation mediated by heteronuclear metal clusters. The results provide new insights into the SEM in which active V-Al cooperative communication favors the transfer of an unpaired electron from the V atom to NO attached to the Al atom on which the reduction reaction actually takes place. This study provides a clear picture for improving our understanding of related heterogeneous catalysis, and the electron hopping behavior induced by NO adsorption could be a fundamental chemistry for driving NO reduction.

An organic-inorganic diamine, 1,3-bis(aminopropyl)tetraphenyldisiloxane, was prepared and introduced as a flexible spacer into the structure of a salen-type Schiff base (H2L7) extending the available small library of similar compounds derived from 1,3-bis(aminopropyl)tetramethyldisiloxane and substituted 2-hydroxybenzaldehydes (H2L1-H2L6). Like the previously reported mononuclear copper(II) complexes [CuL1]-[CuL6], the new copper(II) complex [CuL7], obtained by reaction of Cu(OAc)2·H2O with H2L7 in a mixture of organic solvents, has a tetrahedrally distorted square-planar (N2O2) coordination geometry. X-ray crystallography has shown that compared to [CuL1]-[CuL6] the Si-O-Si angle in [CuL7] is even closer to linear due to stronger intramolecular interactions between Ph groups than between Me groups in the central-R2Si-O-SiR2- fragment (R = Ph and Me, respectively). [CuL7] can be electrochemically reversibly oxidised by two successive one-electron processes, generating stable phenoxyl mono- and diradicals. Both oxidations are ligand-centred, leading to the formation of coordinated phenoxyl radicals. The UV spectrum of [CuL7] consists of π → π* and LMCT σ → d transitions. The low-energy d-d absorption is well described by AILFT CAS(9,5)/NEVPT2 calculations. The one-electron oxidised compound [CuL7]+ should exist in the triplet ground state as 3[CuL7]+ with one unpaired electron located on the dx2-y2 orbital of copper(II) (d9, SCu = ½) and another electron on the molecular orbital (MO) comprising pz oxygen and carbon atoms of the phenoxyl radical (Srad = ½). The broad absorption in the vis-NIR region of the optical spectrum of the one-electron oxidised complex is due to intervalence charge transfer in the triplet species 3[CuL7]+, but not in the [CuL7]2+ one. The doubly oxidised [CuL7] species shows very close doublet and quartet states, where the doublet state has an unpaired electron located on the Cu(II) d-orbital, while the quartet state has one unpaired electron on the Cu(II) d-orbital and two unpaired electrons on π-bonding orbitals. In all state-averaged CASSCF cases, the occupation of the Cu(II) d-orbital is nearly 1.0, indicating its limited involvement in the excited states. Catalytic studies showed that [CuL7] acts as a catalyst for the oxidation of alkanes with peroxides under very unusual solvent-free conditions, converting cyclohexane into cyclohexanol and cyclohexanone (with hydrogen peroxide or tert-butyl hydroperoxide as the oxidant) or into cyclohexanol and ε-caprolactone (with m-chloroperoxybenzoic acid as the oxidant). Theoretical investigations of the catalytic reaction mechanisms disclosed the principal intermediates.