光催化分解水制氢

… into H 2 and O 2 using semiconductor photocatalysts (sometimes called artificial … photocatalysts for overall water splitting. In particular, the Primer covers various pitfalls in photocatalysis …

Photocatalytic water splitting using sunlight is a promising technology capable of providing high energy yield without pollutant byproducts. Herein, we review various aspects of this technology including chemical reactions, physiochemical conditions and photocatalyst types such as metal oxides, sulfides, nitrides, nanocomposites, and doped materials followed by recent advances in computational modeling of photoactive materials. As the best-known catalyst for photocatalytic hydrogen and oxygen evolution, TiO2 is discussed in a separate section, along with its challenges such as the wide band gap, large overpotential for hydrogen evolution, and rapid recombination of produced electron-hole pairs. Various approaches are addressed to overcome these shortcomings, such as doping with different elements, heterojunction catalysts, noble metal deposition, and surface modification. Development of a photocatalytic corrosion resistant, visible light absorbing, defect-tuned material with small particle size is the key to complete the sunlight to hydrogen cycle efficiently. Computational studies have opened new avenues to understand and predict the electronic density of states and band structure of advanced materials and could pave the way for the rational design of efficient photocatalysts for water splitting. Future directions are focused on developing innovative junction architectures, novel synthesis methods and optimizing the existing active materials to enhance charge transfer, visible light absorption, reducing the gas evolution overpotential and maintaining chemical and physical stability.

Currently, problems associated with energy and environment have become increasingly serious. Producing hydrogen, a clean and renewable resource, through photocatalytic water splitting using solar energy is a feasible and efficient route for resolving these problems, and great efforts have been devoted to improve the solar‐to‐hydrogen efficiency. Light harvesting and electron–hole separation are key in enhancing the efficiency of solar energy utilization, which stimulates the development of new photocatalytic materials. Here, recent advances in material design for photocatalytic water splitting are presented from a theoretical perspective. Specifically, aiming to enhance the photocatalytic performance, general strategies of materials design are discussed, including codoping and introducing a built‐in electric field to improve the light harvesting of materials, reducing the dimension of materials to shorten the migration pathway of carriers to inhibit electron–hole recombination, and constructing heterojunctions to enhance light harvesting and electron–hole separation. Future opportunities and challenges in the theoretical design of photocatalytic materials toward water splitting are also included.

… and future challenges in photocatalytic water splitting, with a … , photocatalytic activity for overall water splitting is strongly dependent on the physicochemical properties of a photocatalyst, …

A widely used term, “photocatalysis”, generally addresses photocatalytic (energetically downhill) and photosynthetic (energetically uphill) reactions and refers to the use of photonic energy as a driving force for chemical transformations, i.e., electron reorganization to form/break chemical bonds. Although there are many such important reactions, this contribution focuses on the fundamental aspects of photocatalytic water splitting into hydrogen and oxygen by using light from the solar spectrum, which is one of the most investigated photosynthetic reactions. Photocatalytic water splitting using solar energy is considered to be artificial photosynthesis that produces a solar fuel because the reaction mimics nature’s photosynthesis not only in its redox reaction type but also in its thermodynamics (water splitting: 1.23 eV vs glucose formation: 1.24 eV). To achieve efficient photocatalytic water splitting, all of the parameters, though involved at different time scales and spatial resolutions, should be op...

… for overall water splitting. Our work demonstrates the feasibility of overall water splitting free … losses and introduces an ideal cocatalyst/photocatalyst structure for efficient water splitting. …

… is photoelectrochemical water splitting, … water splitting can be regarded as an intermediate approach between photovoltaic-assisted water electrolysis and photocatalytic water splitting 5,…

This paper examines photocatalytic hydrogen production as a clean energy solution to address challenges of climate change and environmental sustainability. Advantages and disadvantages of various hydrogen production methods, with a particular emphasis on photocatalytic hydrogen production, are discussed in this paper. Social, environmental and economic aspects are taken into account while assessing selected production methods and types of photocatalysts. In the first part of this paper, various hydrogen production options are introduced and comparatively assessed. Then, solar‐based hydrogen production options are examined in a more detailed manner along with a comparative performance assessment. Next, photocatalytic hydrogen production options are introduced, photocatalysis mechanisms and principles are discussed and the main groups of photocatalysts, namely titanium oxide, cadmium sulfide, zinc oxide/sulfide and other metal oxide‐based photocatalyst groups, are introduced. After discussing recycling issues of photocatalysts, a comparative performance assessment is conducted based on hydrogen production processes (both per mass and surface area of photocatalysts), band gaps and quantum yields. The results show that among individual photocatalysts, on average, Au–CdS has the best performance when band gap, quantum yield and hydrogen production rates are considered. From this perspective, TiO2–ZnO has the poorest performance. Among the photocatalyst groups, cadmium sulfides have the best average performance, while other metal oxides show the poorest rankings, on average. Copyright © 2016 John Wiley & Sons, Ltd.

An overview of the advantages and challenges of photocatalytic water splitting is provided to encourage new research directions mainly on data reproducibility and photocatalyst scalability.

… Photocatalytic water splitting represents a promising strategy … steps for the photocatalytic water splitting reaction: solar light … first two steps in the photocatalytic process, much less efforts …

Over the past decades, various photocatalysts have been developed and great progress has been achieved in the field of solar-driven photocatalytic water splitting. However, the lack of an accurate and comprehensive evaluation method greatly hinders the meaningful comparison between different systems and becomes a serious impediment for the development of photocatalysts. Although many researchers are aware of this, there has been little work in this area. In this Viewpoint, we first analyze the insufficiencies of the existing evaluation methods and then make preliminary suggestions, aiming to stimulate discussion in the research community and hopefully lead to a widely accepted and authoritative evaluation system to assess photocatalyst performance.

Abstract Solar light-driven water splitting provides a promising way to store and use abundant solar energy in the form of gaseous hydrogen which is the cleanest chemical fuel for mankind; therefore this field has been attracting increasing attention over the past decades. The fundamental steps for efficient photocatalyst for water splitting include uptake of photons of targeted energy range by appropriate electronic band structure, excited electrons and holes (excitons) migration, as well as recombination and selective conversion excited electrons for H+ reduction to H2 and holes and OH− to O2 on catalyst surface. Each step if not efficiently taken place could hamper the overall photocatalytic activity. Numerous semiconductors with appropriate bandgaps have mainly been developed as candidates for effective solar energy capture, whereas at present, their low quantum efficiency still remains as the major obstacle in further applications. In this minireview, we will disentangle the progress to develop photocatalysts with good photon uptake from photocatalytic water splitting performance. In accordance with the thermodynamic and kinetic considerations of the photocatalytic water splitting reaction, different strategies for improving the fundamental processes have been briefly reviewed. Some recent advances in facilitating charge carriers separation have also been presented. Photocatalytic water splitting at elevated temperatures is emphasized as a novel approach to suppress photo-excitons recombination on catalyst surface owing to adsorption of enhanced concentration of ionic species including H+ and OH− to create their local polarization to the excitons. Stronger polarization to hinder the excitons recombination can also be obtained by using polar-faceted support materials to the active phase of semiconductor. It is clearly demonstrated in this minireview that such high temperature–promoted photocatalytic water splitting systems could open up a new direction and provide a new innovation to this field.

… and participate in reduction and oxidation of adsorbed water molecules [4 • ]. Each of the steps involved in photocatalytic water splitting play a critical role in determining the overall …

… the photocatalyst with … photocatalytic materials has relied on both photocatalysts and cocatalysts. This review article describes the historical development of water-splitting photocatalysts…

Understanding the water splitting mechanism in photocatalysis is a rewarding goal as it will allow producing clean fuel for a sustainable life in the future. However, identifying the photocatalytic mechanisms by modeling photoactive nanoparticles requires sophisticated computational techniques based on multiscale modeling. In this review, we will survey the strengths and drawbacks of currently available theoretical methods at different length and accuracy scales. Understanding the surface-active site through Density Functional Theory (DFT) using new, more accurate exchange-correlation functionals plays a key role for surface engineering. Larger scale dynamics of the catalyst/electrolyte interface can be treated with Molecular Dynamics albeit there is a need for more generalizations of force fields. Monte Carlo and Continuum Modeling techniques are so far not the prominent path for modeling water splitting but interest is growing due to the lower computational cost and the feasibility to compare the modeling outcome directly to experimental data. The future challenges in modeling complex nano-photocatalysts involve combining different methods in a hierarchical way so that resources are spent wisely at each length scale, as well as accounting for excited states chemistry that is important for photocatalysis, a path that will bring devices closer to the theoretical limit of photocatalytic efficiency.

Sunlight-driven photocatalytic water splitting is one of the most promising approaches to generating renewable hydrogen as an energy source. In recent years, significant progress has been made in the development of photocatalytic water-splitting systems. Among these, the one- and two-step-excitation overall water-splitting processes are most widely investigated. Realization of visible-light-driven overall water splitting is one of the most important goals at present because of the need to obtain systems exhibiting high solar-to-hydrogen energy conversion efficiency for practical applications. The present review focuses on recent progress in the field of photocatalytic water splitting, especially in the research and design of visible-light-driven overall water-splitting systems, and outlines potential strategies to overcome the difficulties related to practical applications.

The development of clean and renewable energy materials as alternatives to fossil fuels is foreseen as a potential solution to the crucial problems of environmental pollution and energy shortages. Hydrogen is an ideal energy material for the future, and water splitting using solar/electrical energy is one way to generate hydrogen. Metal‐organic frameworks (MOFs) are a class of porous materials with unique properties that have received rapidly growing attention in recent years for applications in water splitting due to their remarkable design flexibility, ultra‐large surface‐to‐volume ratios and tunable pore channels. This review focuses on recent progress in the application of MOFs in electrocatalytic and photocatalytic water splitting for hydrogen generation, including both oxygen and hydrogen evolution. It starts with the fundamentals of electrocatalytic and photocatalytic water splitting and the related factors to determine the catalytic activity. The recent progress in the exploitation of MOFs for water splitting is then summarized, and strategies for designing MOF‐based catalysts for electrocatalytic and photocatalytic water splitting are presented. Finally, major challenges in the field of water splitting are highlighted, and some perspectives of MOF‐based catalysts for water splitting are proposed.

Graphene oxide (GO) sheets have highly tunable electronic properties because of their unique 2D carbon structure, which allows extensive modification with surface functionalities. Photo-driven water splitting uses semiconducting materials that have electronic structures suitable for electron and hole injection for H2 and O2 evolution from water decomposition. GO is an ideal material to mediate photogenerated charges for water decomposition. This paper introduces strategies for tuning the electronic structure of GO and presents GO, alone and with other materials, as a mediator for photocatalytic water splitting.

… Therefore, we organize such a review and focus on screening 2D materials for photocatalytic water splitting. In this review, we discuss the discovery of 2D photocatalysis from a …

… of photocatalytic water splitting and the concept of different kinds of photocatalytic water splitting … strategies for searching more efficient photocatalysts will be presented with selected …

This review focuses on the efficiency of different nanomaterials used in photocatalytic hydrogen production. Some 200 articles were reviewed for photocatalytic hydrogen production (…

… Unfortunately, the hydrogen production efficiency of single phase photocatalysts is too low to … rational design and fabrication of nanoheterostructured photocatalysts. The heterojunction …

… Photocatalytic hydrogen (H 2) production represents a very promising but challenging … The photocatalyst material plays a key role in photocatalytic H 2 production, and it has proven …

Hydrogen represents a renewable energy alternative that may positively contribute to get over the global energy crisis while at the same time reducing its environmental burden. Overcoming the challenge of reaching this potential could be helped by careful choice of hydrogen (H₂) sources. Photocatalytic generation of H₂, although a minor alternative, appears to be a very good option at the time that liquid wastes are being degraded; therefore, this approach has given rise to an increasing number of interesting studies. Here, we aim to provide an integrated overview of the different photocatalytic, heterogeneous, homogeneous and hybrid systems. First, we categorize the units and mechanisms that take part in the photocatalytic process, and secondly we analyze their role and draw comparative conclusions. Thus, we analyze the role of (i) the electron source to carry out proton reduction, (ii) the proton source, which can be free protons in the medium or a proton donor compound, (iii) the catalyst nature and concentration, and (iv) the photosensitizer nature and concentration. We also provide an analysis of the influence of the solvent, especially in homogenous systems as well as the influence of pH. We provide a comparison of the photocatalytic performance, highlighting the advantages and disadvantages, of different systems. Thus, this review is, on the one hand, an update on the state of the art of photocatalytic generation of H₂ from a full perspective that integrates homogeneous, heterogeneous and hybrid systems, and, on the other, a source of useful information for future research. © 2019 Society of Chemical Industry

… source such as solar energy, hydrogen can then be considered a green … of photocatalytic hydrogen generation in the hydrogen energy system. Such an approach to energy production …

Energy shortage and environmental pollution are two major issues hindering the sustainability of modern civilization. Photocatalytic water decomposition provides a promising approach to harvest solar energy for generating environmental-friendly hydrogen...

… Photocatalytic hydrogen production using semiconductor … Sulphide semiconductor photocatalysts have attracted much … clean energy future by photocatalytic hydrogen production. …

… photocatalysts and cocatalysts, modification of photocatalysts, the morphology control of photocatalyst, … photocatalytic hydrogen production systems from water and biomass derivatives. …

Solar-driven hydrogen production from water using particulate photocatalysts is considered the most economical and effective approach to produce hydrogen fuel with little environmental concern. However, the efficiency of hydrogen production from water in particulate photocatalysis systems is still low. Here, we propose an efficient biphase photocatalytic system composed of integrated photothermal–photocatalytic materials that use charred wood substrates to convert liquid water to water steam, simultaneously splitting hydrogen under light illumination without additional energy. The photothermal–photocatalytic system exhibits biphase interfaces of photothermally-generated steam/photocatalyst/hydrogen, which significantly reduce the interface barrier and drastically lower the transport resistance of the hydrogen gas by nearly two orders of magnitude. In this work, an impressive hydrogen production rate up to 220.74 μmol h−1 cm−2 in the particulate photocatalytic systems has been achieved based on the wood/CoO system, demonstrating that the photothermal–photocatalytic biphase system is cost-effective and greatly advantageous for practical applications. The solar-driven H2 production from water by particulate photocatalysts is an effective approach to produce H2 fuel. Here, the authors propose an integrated photothermal–photocatalytic biphase system, which lowers the reaction barrier and the delivery resistance of the H2, boosting the catalytic H2 evolution rate.

… As an ideal secondary energy source, hydrogen has the title … Photocatalytic hydrogen production technology is an … heterojunction photocatalysts for photocatalytic hydrogen production, …

Abstract Owing to the structural controllability, pore modification and unique semiconductor property of metal-organic frameworks (MOFs), the investigation on MOFs as efficient photocatalysts for hydrogen production from water splitting under UV, visible or even NIR light irradiation have made great progress. In this review, we systematically summarized the recent advances of MOFs-based photocatalysts for hydrogen production from water, and divided them into three categories: MOFs, MOFs composites and MOFs-derived photocatalysts. The high hydrogen production efficiency and possible hydrogen production mechanism of MOFs-based photocatalysts were analyzed in detail. A brief perspective was given to achieve high effective and stable MOFs-based materials for photolysis of water, providing suggestions to explore new and efficient MOFs-based photocatalysts.

Abstract Hydrogen represents a clean and sustainable energy source with wide applications in fuel cells and hydrogen energy storage systems. Photocatalytic strategies emerge as a green and promising solution for hydrogen production, which still reveals several critical challenges in enhancing the efficiency and stability and improving the whole value. This review systematically elaborates on various coupling approaches for photocatalytic hydrogen production, aiming to improve both efficiency and value through different oxidation half‐reactions. Firstly, the fundamental mechanism is discussed for photocatalytic hydrogen production. Then, the advances, challenges, and opportunities are expanded for the coupling of photocatalytic hydrogen production, which focuses on the integration of value‐added reactions including O 2 production, H 2 O 2 production, biomass conversion, alcohol oxidation, and pollutants treatment. Finally, the challenges and outlook of photocatalytic H 2 production technology are analyzed from the aspects of coupling hydrogen production value, photocatalyst design and reaction system construction. This work presents a holistic view of the field, emphasizing the synergistic benefits of coupled reactions and their practical application potential, rather than focusing on catalysts or single reaction systems. This review provides valuable references for the development and application of photocatalytic hydrogen production in energy conversion and environmental conservation through sustainable, eco‐friendly and economic pathways.

… we report that hydrogen could be produced … photocatalyst with high efficiency to demonstrate PWS. Thus we employed three systems to evaluate the photocatalytic hydrogen production …

… Sun god: Photocatalytic hydrogen production from water and … process for efficient energy production. In this Review, the … on the development of novel photocatalysts is presented with …

The increasing interest and applications of photocatalysis, namely hydrogen production, artificial photosynthesis, and water remediation and disinfection, still face several drawbacks that prevent this technology from being fully implemented at the industrial level. The need to improve the performance of photocatalytic processes and extend their potential working under visible light has boosted the synthesis of new and more efficient semiconductor materials. Thus far, semiconductor–semiconductor heterojunction is the most remarkable alternative. Not only are the characteristics of the new materials relevant to the process performance, but also a deep understanding of the charge transfer mechanisms and the relationship with the process variables and nature of the semiconductors. However, there are several different charge transfer mechanisms responsible for the activity of the composites regardless the synthesis materials. In fact, different mechanisms can be carried out for the same junction. Focusing primarily on the photocatalytic generation of hydrogen, the objective of this review is to unravel the charge transfer mechanisms after the in-depth analyses of already reported literature and establish the guidelines for future research.

… the electron transfer and enhances the photocatalytic activity. This work shows not … photocatalytic H 2 -production but also demonstrates a new way for enhancing hydrogen production …

… of photocatalytic hydrogen production process were studied, which include: photocatalyst type and its … The prepared photocatalyst gave good results for the hydrogen production rate. …

Abstract Searching a sustainable way to efficiently produce hydrogen (H2) is critical to realizing the “hydrogen economy”, which may resolve the global energy and environmental issues nowadays. The conversion of solar energy to hydrogen energy based on photocatalytic water splitting is an ideal technology for environmental-friendly and economically producing H2. Exploring high-performance and earth-abundant cocatalysts that can replace noble metal-based cocatalysts is essential to achieving highly efficient and cost-effective photocatalytic H2 production. In recent years, transition metal phosphides (TMPs) have been regarded as promising candidates to replace noble metal-based cocatalysts for photocatalytic H2 production. This review presents a panorama of the latest progress in the developments of TMPs for photocatalytic H2 production. Concretely, this review starts with the functions of TMPs in photocatalytic H2 production, followed by the synthetic strategies of TMPs and the loading methods of TMPs on semiconductors. Then the application and mechanism of the common TMPs in photocatalytic H2 production are discussed in detail, including iron phosphides, cobalt phosphides and nickel phosphides. Lastly, we provide a comprehensive conclusion and outlook on the major challenges and opportunities for better developments in the future research. It is reasonable to believe that the TMPs is a rising star in photocatalytic H2 production.

Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

… This article will introduce the basic principles of solar water splitting and highlight recent … Separate articles in this special issue will focus on recent developments in watersplitting …

… from solar-driven water-splitting has the potential to be a clean, sustainable and abundant energy source. Inspired by natural photosynthesis, artificial solar water-splitting devices are …

… solar energy that can be used on demand on a global scale. Solar water splitting provides a scalable route to store solar … directly used in a fuel cell with water as the only emission or as …

… Photocatalytic (PC) or photoelectrochemical (PEC) water splitting (WS) into H 2 and O 2 using solar energy and semiconductors (SCs) is a promising way to solve both the solar energy …

Photoelectrochemical (PEC) water splitting has been intensively studied in the past decades as a promising method for large-scale solar energy storage. Among the various issues that limit the progress of this field, the lack of photoelectrode materials with suitable properties in all aspects of light absorption, charge separation and transport, and charge transfer is a key challenge, which has attracted tremendous research attention. A large variety of compositions, in different forms, have been tested. This review aims to summarize efforts in this area, with a focus on materials-related considerations. Issues discussed by this review include synthesis, optoelectronic properties, charge behaviors and catalysis. In the recognition that thin-film materials are representative model systems for the study of these issues, we elected to focus on this form, so as to provide a concise and coherent account on the different strategies that have been proposed and tested. Because practical implementation is of paramount importance to the eventual realization of using solar fuel for solar energy storage, we pay particular attention to strategies proposed to address the stability and catalytic issues, which are two key factors limiting the implementation of efficient photoelectrode materials. To keep the overall discussion focused, all discussions were presented within the context of water splitting reactions. How the thin-film systems may be applied for fundamental studies of the water splitting chemical mechanisms and how to use the model system to test device engineering design strategies are discussed.

… The key of a successful solar-to-fuel technology is the design … for absorbing sunlight and driving water splitting reactions. To this … interfaces for solar water splitting applications using first-…

It is widely accepted within the community that to achieve a sustainable society with an energy mix primarily based on solar energy we need an efficient strategy to convert and store sunlight into chemical fuels. A photoelectrochemical (PEC) device would therefore play a key role in offering the possibility of carbon-neutral solar fuel production through artificial photosynthesis. The past five years have seen a surge in the development of promising semiconductor materials. In addition, low-cost earth-abundant co-catalysts are ubiquitous in their employment in water splitting cells due to the sluggish kinetics of the oxygen evolution reaction (OER). This review commences with a fundamental understanding of semiconductor properties and charge transfer processes in a PEC device. We then describe various configurations of PEC devices, including single light-absorber cells and multi light-absorber devices (PEC, PV-PEC and PV/electrolyser tandem cell). Recent progress on both photoelectrode materials (light absorbers) and electrocatalysts is summarized, and important factors which dominate photoelectrode performance, including light absorption, charge separation and transport, surface chemical reaction rate and the stability of the photoanode, are discussed. Controlling semiconductor properties is the primary concern in developing materials for solar water splitting. Accordingly, strategies to address the challenges for materials development in this area, such as the adoption of smart architectures, innovative device configuration design, co-catalyst loading, and surface protection layer deposition, are outlined throughout the text, to deliver a highly efficient and stable PEC device for water splitting.

Reliable measurement of the photoconversion efficiency for semiconductor electrodes is essential to the assessment of electrode performance. In this paper, the influence of the choice …

… water splitting, an ideal PEC cell with high solar energy to … for water splitting. In this review, recent progresses in photoelectrocatalytic materials for photoelectrocatalytic water splitting …

… with champion solar cells 10,11 , these are nanostructures that provide the highest solar conversion … Among the nanoparticle-based electrodes used in solar water-splitting, α-Fe 2 O 3 (…

… water splitting involves complicated photoelectrochemical processes (Scheme 1). During the photocatalytic water splitting … solar irradiation and realize overall solar water splitting. …

… development of plasmonics for water splitting and, more broadly, solar-to-chemical … water splitting, because this area provides the clearest examples of plasmon-enhanced water splitting…

… of enhanced solar PC H 2 production from water splitting is the focus of this study. More examples of Cu acting as the cocatalyst in PC H 2 production from water reduction can be found …

… of solar energy, solar water splitting is remarkable since it can accomplish the conversion of solar … are the research focuses for the solar water splitting. Tantalum-based semiconductors, …

… As the most commonly encountered form of iron oxide in nature, hematite is a semiconducting crystal with an almost ideal bandgap for solar water splitting. Compelled by this unique …

… Solar water splitting provides a sustainable and environmentally … photoelectrochemical cell (PEC) for water splitting using TiO 2 as a … The key components of the water-splitting PEC are …

… means of water splitting over semiconductor photocatalysts is a … numerous photocatalytic materials and water-splitting systems … with solar water splitting by particulate photocatalysts for …

Overall water splitting based on particulate photocatalysts is an easily constructed and cost-effective technology for the conversion of abundant solar energy into clean and renewable hydrogen energy on a large scale. This promising technology can be achieved in a one-step excitation system using a single photocatalyst or via a Z-scheme process based on a pair of photocatalysts. Ideally, such photocatalysis will proceed with charge separation and transport unaffected by recombination and trapping, and surface catalytic processes will not involve undesirable reactions. This review summarizes the basics of overall water splitting via both one-step excitation and Z-scheme processes, with a focus on standard methods of determining photocatalytic performance. Various surface engineering strategies applied to photocatalysts, such as cocatalyst loading, surface morphology control, surface modification and surface phase junctions, have been developed to allow efficient one-step excitation overall water splitting. In addition, numerous visible-light-responsive photocatalysts have been successfully utilized as H2-evolution or O2-evolution photocatalysts in Z-scheme overall water splitting. Prototype particulate immobilization systems with photocatalytic performances comparable to or drastically higher than those of particle suspension systems suggest the exciting possibility of the large-scale production of low-cost renewable solar hydrogen.

… first successful example of overall water splitting induced by … An interesting and useful effect on overall water splitting … 2 , a typical photocatalyst, cannot decompose water in an aqueous …

… Photocatalytic overall water splitting is projected as a potential … This paper argues that photocatalytic overall water splitting is … of the photocatalytic overall water splitting and analyze the …

… overall water splitting and give an outlook for future research. … on the photocatalysis for overall water splitting is lacking, and… direction of the cleavage of pure water. Herein, we contribute …

Converting solar energy into storable and transportable chemical fuels using artificial photosynthetic systems can provide an alternative route to the current unsustainable use of fossil fuels, addressing the worldwide energy crisis and environmental issues. Recently, semiconducting polymers have emerged as a very promising class of photocatalysts for water splitting as their electronic and structural properties can be conveniently controlled and systematically designed at a molecular level. Among the various polymer photocatalysts that are reported so far, 2D polymer nanosheets are particularly interesting and gaining more attention. The 2D planar structure offers unique features such as high surface area, abundant surface active sites, efficient charge separation, and facile formation of heterostructures. The design and synthesis of 2D polymer nanosheets have greatly advanced the research in photocatalytic overall water splitting. Here, recent advances in developing photocatalysts based on 2D polymer nanosheets for photocatalytic overall water splitting are highlighted. Specifically, the existing approaches to tune their electronic structures and surface active sites for photocatalysis are discussed. Future opportunities and challenges for developing 2D polymers for photocatalytic overall water splitting are also included.

ConspectusSunlight-driven one-step-excitation overall water splitting (OWS) using a single particulate photocatalyst is a simple and cost-effective approach to producing sustainable hydrogen on a large scale, providing an important impetus to achieving a carbon-neutral society. Technoeconomic studies have determined that a minimum solar-to-hydrogen (STH) energy conversion efficiency of 5% must be achieved to allow this process to be economically competitive. Meeting this goal will require the fabrication of particulate photocatalysts comprising composites of semiconductors and cocatalysts that are sufficiently active under sunlight. A one-step-excitation OWS system based on a metal oxide semiconductor having a wide bandgap was first reported in 1980, and the performance of such systems has been improved significantly over the past decade. In particular, work by the authors' group increased the apparent quantum yield (AQY) obtainable for ultraviolet (UV)-active SrTiO3 to more than 90% in 2020. However, the STH conversion efficiency of a photocatalyst that absorbs only UV light (that is, λ < 400 nm) is limited to 1.7% even at an AQY of unity. It is therefore highly important to develop one-step-excitation OWS processes utilizing narrow bandgap photocatalysts having absorption edge wavelengths equal to or longer than 500 nm. Such systems would be expected to meet the desired 5% STH energy conversion efficiency once a constant AQY of approximately 63% is obtained.This Account summarizes the development and application of narrow-band-gap (oxy)nitride and oxysulfide photocatalysts in the authors' laboratory that are able to split water in response to wavelengths as high as 500 to 650 nm via single-step photoexcitation. At first, the authors briefly recount the key steps required to progress from the initial utilization of a UV-active SrTiO3 photocatalyst as an OWS-active material to the realization of an AQY of almost unity. Multiple design and refinement strategies applied to both the semiconductor and cocatalysts associated with this benchmark photocatalyst are summarized, providing insights into the rational design of narrow-band-gap OWS-active photocatalysts. Furthermore, the necessity, target, and current status of developing narrow-band-gap OWS-active photocatalysts are discussed, followed by a comprehensive discussion of progress in the fabrication of OWS-active (oxy)nitride and oxysulfide photocatalysts with absorption edge wavelengths at up to the range of 500-650 nm in our laboratory. Specific examples are used to show the importance of several factors. First, adjusting the properties of the semiconducting material based on designing appropriate precursors, optimizing the synthetic conditions and aliovalent doping is described. Second, loading of efficient dual cocatalysts is examined. Lastly, the effectiveness of coating the particulate photocatalysts with surface nanolayers is addressed. Deficits related to the performance of present-day photocatalysts are also evaluated. Expectations with regard to future improvements of (oxy)nitride- and oxysulfide-based photocatalysts as a means of increasing the AQY are considered. The strategies summarized in this Account are expected to promote the development of nonsacrificial long-wavelength-responsive photosynthesis systems using water as a hydrogen/oxygen source.

Abstract In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co‐catalyst (e.g. Pt). For pursuing a carbon neutral and cost‐effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench‐top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half‐reaction, and have so far shown limited success in hydrogen production from overall water‐splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water‐splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar‐to‐hydrogen) conversion efficiency.

… photocatalytic overall water splitting (POWS) reaction can take place on TiO 2 -based photocatalysts … We found that the stable overall water splitting with stoichiometric H 2 /O 2 ratio can …

Photocatalyst overall water splitting is usually restricted by low carrier separation efficiency and a slow surface reaction rate. Cocatalysts provide a satisfactory solution to significantly improve photocatalytic performance. In this review, some recent advances in cocatalysts for photocatalytic overall water splitting are gathered and divided into groups. Firstly, the loading method of the cocatalyst is introduced. Then, the role of the cocatalyst applied for the photocatalytic overall water splitting process is further discussed. Finally, the key challenges and possible research directions of photocatalytic overall water splitting are proposed. This review is expected to promote research on the design of efficient cocatalysts in photocatalytic systems for overall water splitting.

… a bandgap of 1.9 eV, as a photocatalyst for overall water splitting. On loading of IrO 2 and Rh/… The discovery of the overall water splitting capabilities of Y 2 Ti 2 O 5 S 2 extends the range …

Photocatalytic overall water splitting (OWS) without using any sacrificial reagent to realize H 2 and O 2 production in the stoichiometric ratio of 2:1 is viewed as the “ holy grail ” in the field of solar fuel production. Developing stable, low cost, and nontoxic photocatalysts that have satisfactory solar-to-hydrogen conversion efficiency is of significance but challenging for realizing the large-scale use of this sustainable technology. Among various photocatalysts, graphitic carbon nitride (GCN) has shown great potential as an ideal candidate to fulfill the breakthrough in this dynamic research field due to its attractive physicochemical properties. Herein, for the first time, the state-of-the-art research progress of GCN for photocatalytic OWS is reviewed. We first summarize the basic principle of photocatalytic OWS along with the advan-tages/challenges of GCN introduced. The strategies that have been used to modulate the OWS activity of GCN are then reviewed, including cocatalyst investigation, morphology modulation, atomic structure modification, crystallinity engineering, and heterostructure construction. Toward the end of the review, the concluding remarks and perspectives for the future development are presented, with our expectation to provide some new ideas for the design of advanced OWS photocatalysts.

Photocatalytic splitting of water with solar energy is considered as the most promising approach for the production of hydrogen fuel. However, its solar to hydrogen conversion efficiency is much below the industrial requirement (10%). This situation has stimulated intensive efforts to improve photocatalytic overall water splitting (namely, simultaneously providing unassisted oxidation and reduction of water), leading to the invention of novel catalysts in the recent years. The evaluation of these recent progresses constitutes this review article, with emphasis on the strategies employed for the development of catalysts. The catalysts were deeply reviewed and were classified into four types: (a) perovskite compounds, (b) metal oxides (sulfides and nitrides), (c) Bi‐ and In‐based materials, and (d) multicomponent catalysts. Furthermore, the challenges that remain with the process and catalysts and the potential advances were discussed as an outlook for future research.

… In this respect, heterogeneous particulate photocatalytic overall water splitting is one of the most promising systems for sustainable and competitive solar hydrogen generation from an …

… visible-light-driven overall water splitting on a novel oxynitride photocatalyst, a solid solution of … photocatalysts, such as CdS, the solid solution is stable during the overall water splitting …

The development of narrow-bandgap photocatalysts for one-step-excitation overall water splitting (OWS) remains a critical challenge in the field of solar hydrogen production. SrTaO2N is a photocatalytic material having a band structure suitable for OWS under visible light (λ ≤ 600 nm). However, the presence of defects in the oxynitride and the lack of cocatalysts to promote simultaneous hydrogen and oxygen evolution make it challenging to realize OWS using this material. The present work demonstrates a SrTaO2N-based particulate photocatalyst for OWS. This photocatalyst, which was composed of single crystals, was obtained by nitriding SrCl2 and Ta2O5 together with NaOH, with the latter added to control the formation of defects. The subsequent loading of bimetallic RuIrOx nanoparticles accelerated charge separation and allowed the SrTaO2N photocatalyst to exhibit superior OWS activity. This research presenting the strategies of controlling the oxygen sources and promoting the cocatalyst function is expected to expand the range of potential OWS-active oxynitride photocatalysts and permit the design of efficient cocatalysts for photocatalytic OWS.

… in both one-step and two-step (Z-scheme) water splitting systems and presents state-of-the-… recent progress in photocatalytic overall water splitting using SrTiO 3 photocatalyst, primarily …

… photocatalysts and water molecules, necessitating a photon energy greater than the band gap of the photocatalyst to drive the overall water splitting … , that is, water formation from H 2 …

Photocatalytic overall water splitting using cocatalyst-modified photocatalysts faces a significant challenge to achieve highly efficient performance in pure water, as the back reaction─where the evolved H2 and O2 recombine back into H2O─is also catalyzed by the cocatalysts. Overlayers on modified photocatalysts have been reported to prevent the back reaction and significantly enhance the overall water splitting activity. This review provides a comprehensive overview of the use of overlayers in suppressing the back reaction in photocatalytic overall water splitting and their multifunctional roles in facilitating charge separation and transport, and stabilizing cocatalysts and photocatalysts. The application of overlayers is also explored in suppressing the back reactions in other photocatalytic reactions and systems, including Z-scheme systems, electrochemical and photoelectrochemical water splitting systems, pollutant degradation reactions, and photocatalytic CO2 conversion. Furthermore, this review addresses the challenges facing overlayers, particularly their durability during photoreaction, and suggests future research areas. Overall, the knowledge gained to date emphasizes the potential of overlayers to enhance the efficiency and stability of cocatalyst-modified photocatalysts in the field of photocatalysis.

Abstract The construction of Z-scheme system is a promising approach for photocatalytic hydrogen evolution (PHE). In this study, we fabricated a direct Z-scheme system consisting of defect-rich g-C3N4 nanosheets (DR-CNNS) crumpled nanosheets with defect-rich TiO2 (DR-TiO2) nanoparticles via a dual defective strategy. The optimized dual-defective rich TiO2/CNNS composite showed a superior PHE rate of ˜651.79 μmol/h with a turnover frequency of ˜419.3 h−1 as well as high stability and recyclability, which presented the highest value in single defective TiO2 or g-C3N4-based photocatalysts families reported previously. Furthermore, this protocol could also be extended to synthesize other dual defective g-C3N4/oxides (ZnO, SnO2, etc.) heterostructures. The improved photocatalytic performances could be ascribed to the following aspects: (1) rich dual defect, narrowing the band gap and providing more reactive sites for PHE; (2) intimate interface, facilitating interfacial migration and utilization of photogenerated charges; (3) Z-scheme structure, accelerating photogenerated electron-hole pair separation and thus leading to more efficient PHE. Our work highlights the critical role of defects in construction of Z-scheme system and provides the possibility of utilizing dual defective g-C3N4-based systems for other photocatalytic applications including CO2 reduction and water purification.

… challenges associated with the Z-scheme mechanism. In this … Z-scheme systems, that is, liquid-phase Z-scheme systems, all-solid-state Z-scheme heterojunctions, and direct Z-scheme …

The development of innovative technologies for solar energy conversion and storage is important for solving the global warming problem and for establishing a sustainable society. The photocatalytic water‐splitting reaction using semiconductor powders has been intensively studied as a promising technology for direct and simple solar energy conversion. However, the evolution of H2 and O2 gases in a stoichiometric ratio (H2/O2 = 2) is very difficult owing to various issues, such as an unfavorable backward reaction and mismatched band potentials. Two important findings have widened the variety of photocatalysts available for stoichiometric water‐splitting, viz. the carbonate anion effect and the Z‐scheme photocatalytic reaction using a redox mediator. The bicarbonate anion has been found to act as a redox catalyst via preferential peroxide formation and subsequent decomposition to O2. As the Z‐scheme reaction using a redox mediator mitigates band potential mismatches, it is widely applicable for various visible‐light‐active photocatalysts. This review describes the development of photocatalytic water‐splitting for solar hydrogen production using the carbonate anion effect and the Z‐scheme reaction. Moreover, recent developments in photocatalysis–electrolysis hybrid systems, an advanced Z‐scheme reaction concept, are also reviewed for practical and economical hydrogen production.

… of the photocatalytic system. Here, the historical development of the Z‐scheme photocatalytic system is summarized, from its first generation (liquid‐phase Z‐scheme photocatalytic …

… photocatalytic activity of the composites highly depended on WO 3 content. The enhanced photocatalytic activity could be ascribed to the Z-scheme … , a typical Z-scheme photocatalyst is …

The construction of Z-scheme heterojunctions has been demonstrated as an effective strategy to improve photocatalytic hydrogen (H2) production efficiency. Herein, a Zn vacancy defect-mediated direct Z-scheme CdS/ZnS (CSZS–VZn) heterojunction was developed to optimize the H2 production performance, and the introduction of cation defects in ZnS could regulate the band structure of the photocatalyst by forming additional energy levels within the band gap and help to form ohmic contacts. The CSZS–VZn heterojunction exhibited a H2 evolution rate of 46.63 mmol h−1 g−1 under visible light illumination in an aqueous Na2S/Na2SO3 system, which was about 388 and 1727 times higher than those of CdS and Zn-vacancy ZnS (ZnS–VZn), respectively. The enhanced photocatalytic activity of CSZS–VZn was mainly attributed to the presence of Zn vacancy defects upon the formation of the Z-scheme heterojunction structure, by which the photogenerated electrons were trapped in the Zn vacancy defect levels of ZnS and recombined with holes in the valence bands of CdS at heterojunction interfaces through ohmic contacts. In such a way, electrons in the conduction bands of CdS were boosted to participate in H2 evolution reactions and photocorrosion was suppressed. This work provides a viable design strategy via the engineering of cation defects in Z-scheme photocatalysts for photocatalytic H2 evolution.

Abstract High efficiency hydrogen generation from water has been achieved in sulfide-polymer heterojunction. In this work, a novel direct Z-scheme CdS/polyimide heterojunction was fabricated by in situ growth of CdS nanoparticles on polyimide (PI) ultrathin nanosheets through solvothermal method. The highest activity achieved on 15%CdS/PI sample reaches to H2-production rate of 613 μmol h−1 g−1 under visible-light irradiation, which is nearly 5 and 60 times higher than that of neat CdS and 1%Pt/PI. Most importantly, the excellent photostability is also achieved over 15% CdS/PI. The enhanced photocatalytic performance and photostability can be attributed to the direct Z-scheme charge transfer in the intimate interfacial between CdS and PI, which accelerates the charges separation and effective suppress of the photocorrosion in CdS/PI heterojunction. The direct Z-scheme charge transfer mechanism is evidenced by in-situ XPS analysis and time-resolved fluorescence (TRPL) decay. This work highlights the role of polymer in constructing efficient sulfide/polymer heterojunction photocatalyst.

… Therefore, a large number of Z-scheme heterojunction … been investigated and used for photocatalytic reactions [10], [11]… can form an artificial Z-scheme photocatalytic system, which can …

Abstract Herein, ZnO/CdS hierarchical composite was prepared through a hydrothermal and chemical bath deposition (CBD) process. Its photocatalytic H2-production performance was tested. Mass ratio of CdS acted a pivotal part in light absorption and photocatalytic properties. Noticeably, promoted photocatalytic H2-production activity of 4134 μmol g−1 h-1 was achieved by the sample with optimal CdS content. Significantly, the photoluminescence (PL) detection of hydroxyl radicals, as well as the in-situ XPS measurements was selected to verify the direct Z-scheme charge migration mechanism. This mechanism endowed the composite with strong capability for hydrogen evolution and elucidated the improved photocatalytic performance. The improvement of photocatalytic activity was due to hierarchical structure, extended visible light response and direct Z-scheme mechanism. This work will give an innovative vision in constructing direct Z-scheme photocatalytic system with great photocatalytic H2-production activity.

… photocatalytic hydrogen evolution from water under visible light, using newly developed direct Z-scheme … The highest rate for hydrogen production reaches 2518 μmol h –1 over optimal …

… by insufficient hole extraction during the photocatalytic reaction, thereby promoting the … /NiWO 4 composite photocatalyst. This study paves the way for constructing other Z-scheme nano-…

Inspired by natural photosynthesis, direct Z-scheme heterostructures are considered as promising photocatalysts for solar-driven water splitting and attract ever-growing interest.

… strong redox ability to the Z-scheme system. Consequently, the simulated solar-light-driven (AM 1.5) photocatalytic H 2 evolution rate of the as-prepared Zn 0.5 Cd 0.5 S-MWCNT-TiO 2 …

… of the Z-scheme heterostructure. The construction of WO 3 /ZIS direct Z-scheme composites … ingenious design of high-performance Z-scheme heterostructured catalysts toward the solar …

Abstract Heterojunction photocatalysts are very promising for solar hydrogen production due to their high efficiency in photo-driven charge generation and separation. A C3N4/ZnO heterostructure nanocomposite harvests a wide range of solar light from the UV and visible regions and retains a high redox potential due to its Z-scheme band structure. However, since both C3N4 and ZnO have sufficiently high conduction band energies to drive hydrogen photoreduction, a type II heterojunction is more beneficial for enhancing the hydrogen production efficiency in the current system. In this study, we first demonstrated the charge transfer mechanism switching from the Z-scheme to type II by simple boron (B) doping of C3N4/ZnO. The doping of C3N4 with low-electronegativity boron increases its Fermi level by 0.4 V, making it even higher than that of ZnO. As a result, the Fermi level alignment of B-doped C3N4 with ZnO causes a reversed band bending direction at the C3N4/ZnO junction. The resultant charge transfer switching from the Z-scheme (C3N4/ZnO) to type II (B-doped C3N4/ZnO) was confirmed by UPS and ESR analysis. Type II B-doped C3N4/ZnO shows a stable, drastic increase in the photocatalytic hydrogen evolution rate, approximately 2.9 times higher than that of undoped C3N4/ZnO. The decreased bandgap energy of B-doped C3N4/ZnO also contributes to an additional improvement in efficiency through enhanced light harvesting. Our work presents a simple but effective strategy to design highly capable heterojunction photocatalysts via charge transfer switching with a doping method.

… Z-scheme photocatalysts have recently received tremendous … This cutting-edge photocatalytic platform allows photocatalysts … (B,C) Visible-light-driven photocatalytic hydrogen evolution …

A photocatalytic Z-scheme system based on 2D/2D WO3/ZnIn2S4 nanocomposite was prepared to generate sustainable hydrogen.

As the world decides on the next giant step for the renewable energy revolution, scientists have begun to reinforce their headlong dives into the exploitation of solar energy. Hitherto, numerous attempts are made to imitate the natural photosynthesis of plants by converting solar energy into chemical fuels which resembles the “Z‐scheme” process. A recreation of this system is witnessed in artificial Z‐scheme photocatalytic water splitting to generate hydrogen (H2). This work outlines the recent significant implication of the Z‐scheme system in photocatalytic water splitting, particularly in the role of electron mediator and the key factors that improve the photocatalytic performance. The Review begins with the fundamental rationales in Z‐scheme water splitting, followed by a survey on the development roadmap of three different generations of Z‐scheme system: 1) PS‐A/D‐PS (first generation), 2) PS‐C‐PS (second generation), and 3) PS‐PS (third generation). Focus is also placed on the scaling up of the “leaf‐to‐tree” challenge of Z‐scheme water splitting system, which is also known as Z‐scheme photocatalyst sheet. A detailed investigation of the Z‐scheme system for achieving H2 evolution from past to present accompanied with in‐depth discussion on the key challenges in the area of Z‐scheme photocatalytic water splitting are provided.

… a Z-scheme gC 3 N 4 /ZnO/Au heterojunction using a simple chemical method for photocatalytic H 2 … friendly Z-scheme heterojunction for photocatalytic H 2 evolution applications. …

… This critical review seeks to give an overview of the concept of heterojunction construction … water splitting photo(electro)catalysts reported over the past ten years. For water splitting, …

… splitting, these drawbacks include massive recombination of charge carriers, limited visible … N 4 -based heterojunction photocatalyst for H 2 production via PC water splitting. The review …

… heterojunction-based photocatalytic system, this review article also provides future directions for photocatalytic water splitting. … various heterojunction strategies applied in water splitting. …

… heterojunction photocatalyst. The CBM of Y layer and VBM of O layer are all located outside the redox potentials of water. … to the redox potentials for water splitting due to a large surface …

… The CdS/Pt is again dispersed in water to simulate photocatalytic water splitting. The lifetime … This work reveals the role of Pt cocatalysts in enhancing the photocatalytic performance of …

… photocatalytic performance. This article reviews the recent progress of CN-based heterojunction photocatalysts for overall water splitting, … principles of different heterojunctions from the …

… TOCN showed higher photocatalytic water splitting activity under simulated sunlight, which is … construct an efficient photocatalyst with S-Scheme heterojunction for overall water splitting. …

… Heterojunction photocatalysts, by tailoring their band structure and lattice matching, … heterojunctions are promising S-scheme photocatalysts for water splitting. In particular, the GaS/SnC …

Abstract An (oxy)nitride‐based heterostructure for powdered Z‐scheme overall water splitting is presented. Compared with the single MgTa 2 O 6− x N y or TaON photocatalyst, a MgTa 2 O 6− x N y /TaON heterostructure fabricated by a simple one‐pot nitridation route was demonstrated to effectively suppress the recombination of carriers by efficient spatial charge separation and decreased defect density. By employing Pt‐loaded MgTa 2 O 6− x N y /TaON as a H 2 ‐evolving photocatalyst, a Z‐scheme overall water splitting system with an apparent quantum efficiency (AQE) of 6.8 % at 420 nm was constructed (PtO x ‐WO 3 and IO 3 − /I − pairs were used as an O 2 ‐evolving photocatalyst and a redox mediator, respectively), the activity of which is circa 7 or 360 times of that using Pt‐TaON or Pt‐MgTa 2 O 6− x N y as a H 2 ‐evolving photocatalyst, respectively. To the best of our knowledge, this is the highest AQE among the powdered Z‐scheme overall water splitting systems ever reported.

Abstract The design of p-n heterojunction photocatalysts to overcome the drawbacks of low photocatalytic activity that results from the recombination of charge carriers and narrow photo-response range is promising technique for future energy. Here, we demonstrate the facile hydrothermal synthesis for the preparation of Bi2O3/MoS2 p-n heterojunction photocatalysts with tunable loading amount of Bi2O3 (0–15 wt%). The structure, surface morphology, composition and optical properties of heterostructures were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL), electrochemical impedance spectroscopy (EIS). Compare to pure Bi2O3 and MoS2, the Bi2O3/MoS2 heterostructures displayed significantly superior performance for photocatalytic hydrogen (H2) production using visible photo-irradiation. The maximum performance for hydrogen evolution was achieved over Bi2O3/MoS2 photocatalyst (10 μmol h−1g−1) with Bi2O3 content of 11 wt%, which was approximately ten times higher than pure Bi2O3 (1.1 μmol h−1g−1) and MoS2 (1.2 μmol h−1g−1) photocatalyst. The superior performance was attributed to the robust light harvesting ability, enhanced charge carrier separation via gradual charge transferred pathway. Moreover, the increased efficiency of Bi2O3/MoS2 heterostructure photocatalyst is discussed through proposed mechanism based on observed performance, band gap and band position calculations, PL and EIS data.

Solar energy to hydrogen production is an effective way to solve the energy crisis. Here, we report a Ti 3 CN@TiO 2 /CdS photocatalyst with highly efficient photocatalytic performance. …

… visible and UV light adsorption, which enable AlN/BP heterostructure to have great potential applications in the field of solar energy conversion and photocatalytic water splitting. …

Summary The significance of photocatalysts is unquestionable, and scientists are devoted to improving their photocatalytic efficiency. To solve the high recombination rates of photogenerated electron-hole pairs and their low reduction and oxidation abilities in a single photocatalyst, heterojunction manipulation is urgently required. Two mainstream heterojunctions—type-II and Z-scheme heterojunctions—have been widely acknowledged. However, we soberly reflect the charge-transfer mechanism from many perspectives and are finally aware of the fundamental challenges they face. To ensure a correct understanding, it is necessary to share our analysis with others. Moreover, step-scheme (S-scheme) heterojunctions, consisting of a reduction photocatalyst and an oxidation photocatalyst with staggered band structure, are introduced to avoid misinterpretation. The differences in the charge-transfer mechanism between S-scheme, type-II, and Z-scheme heterojunctions are highlighted. Finally, limitations and the future research direction of S-scheme photocatalysts are discussed.

… the core–shell shaped xCoS@yTiO 2 heterojunction follows the S-scheme mechanism. The … yTiO 2 heterojunction catalyst is because of its favorable bandgap location for water splitting, …

… heterostructure photocatalysts to enhance the efficiency and stability of photocatalytic water splitting for … In this study, a semiconductor heterostructure photocatalyst composed of CdS …

… ) semiconductor heterostructures for photocatalytic water splitting. … and Z-scheme vdW heterostructure photocatalysts are presented. … for photocatalysts, specifically vdW heterostructures …

… and multicomponent heterojunctions. Several important photocatalytic applications, such as photocatalytic water splitting (H 2 evolution and overall water splitting), degradation of …

Hydrogen production via photocatalytic water splitting using sunlight has enormous potential in solving the worldwide energy and environmental crisis. The key challenge in this …

… Photocatalytic water-splitting … water-splitting photocatalysts (PCs). Adequate light absorption, effective photogenerated carrier separation, and sufficiently large overpotentials for water …

… The excited state of the Re(I) chromophore in 4 could be quenched with unity quantum efficiency either by the ferrocene or by the [FeFe]-H 2 ase mimic. (20) We also synthesized dyad 5 …

… quantum efficiencies of … quantum efficiency obtained from a sample with identical rods but with two Pt tips was only 58.5% (Figure 3). For a multi electron reaction such as hydrogen …

… based on semiconductor technology is very promising for future application of clean energy. However, pure semiconductors usually demonstrate low apparent quantum efficiency (AQE)…

… The essentials of the exceptionally high quantum efficiency (93%) of photocatalytic hydrogen production on Pt–PdS/CdS have been investigated by studying the roles of the dual …

1D semiconductor nanomaterials have generated a high interest in heterogeneous photocatalysis. However, most 1D photocatalysts still suffer from poor charge separation and severe charge recombination. Herein, a unique approach via surface doping of phosphorus (P) atoms into 1D Cd0.5Zn0.5S (CZS) nanorods is demonstrated, leading to an imbalanced charge distribution and a localized built‐in electric field, verified by characterizations including photoluminescence and transient absorption spectra. The CZS‐P nanorods exhibit more than two orders of magnitude enhancement in photocatalytic H2 production activity relative to pristine CZS under visible light. Further construction of spatially separated dual‐cocatalysts (Pt and PdS) on the tip and lateral surface of the CZS‐P nanorods enables a significant improvement in the photocatalytic activity, which results in an apparent quantum efficiency exceeding 89% at 420 nm. Such efficient photocatalytic hydrogen production is attributed to the synergistic effect of tuning the intrinsic built‐in electric field for spatial charge separation and simultaneously accelerating the reduction and oxidation reaction rates utilizing photogenerated charges. The idea of integrating spatial charge separation via morphology tailoring, additional built‐in electric field, and spatial separation of dual‐cocatalysts provides a pathway for rationally designing artificial photocatalysts for solar energy conversion.

… of photocatalytic activity for solar hydrogen evolution. Here we report efficient photo-generated … The quantum efficiency of solar hydrogen evolution over this photocatalyst, without noble …

… hydrogen production with semiconductor particulate systems. Several factors which affect the photocatalytic efficiency … Quantum efficiency of hydrogen production from 0.5 M NaOH (pH 8…

Organic semiconductors offer a tunable platform for photocatalysis, yet the more difficult exciton dissociation, compared to that in inorganic semiconductors, lowers their photocatalytic activities. In this work, we report that the charge carrier lifetime is dramatically prolonged by incorporating a suitable donor-acceptor (β-ketene-cyano) pair into a covalent organic framework nanosheet. These nanosheets show an apparent quantum efficiency up to 82.6% at 450 nm using platinum as co-catalyst for photocatalytic H_2 evolution. Charge carrier kinetic analysis and femtosecond transient absorption spectroscopy characterizations verify that these modified covalent organic framework nanosheets have intrinsically lower exciton binding energies and longer-lived charge carriers than the corresponding nanosheets without the donor-acceptor unit. This work provides a model for gaining insight into the nature of short-lived active species in polymeric organic photocatalysts. While organic semiconductors offer a tunable platform for photocatalysis, they often show worse performances. Here, authors examine how a donor-acceptor pair’s incorporation into a covalent organic framework boosts photocatalytic H_2 evolution performances with a platinum co-catalyst.

We use Pt-decorated CdS nanorods for photocatalytic hydrogen generation in the presence of sacrificial hole scavengers. Both the quantum efficiency for hydrogen generation and the stability of the colloidal nanocrystals in solution improve with increasing redox potential of the hole scavenger. The higher redox potential leads to faster hole scavenging, which increases quantum efficiency and stability since electron hole recombination and oxidation of the CdS become less important. The quantum efficiencies can be tuned over more than an order of magnitude. This finding is important for choosing hole scavengers and for comparing efficiencies and stabilities for different photocatalytic nanosystems.

… To efficiently convert solar energy into chemical energy by artificial photosynthesis, we need to develop visible-light-responsive photocatalysts with a high quantum efficiency (QE). Here …

… the production of chemical fuels, of which molecular hydrogen (H 2 ) is an ideal example in … However, the system affords a solar-to-hydrogen (STH) energy conversion efficiency of only …

Sunlight is an abundant energy source for a sustainable society. Indeed, photosynthetic organisms harness solar radiation to build the world around us by synthesizing energy-rich compounds from water and CO2. However, numerous energy conversion bottlenecks in the natural system limits the overall efficiency of photosynthesis; the most efficient plants do not exceed solar storage efficiencies of 1%. Artificial photosynthetic solar-to-fuels cycles may occur at higher intrinsic efficiencies, but they typically terminate at hydrogen, with no process installed to complete the cycle for carbon fixation. This limitation may be overcome by interfacing solar-driven water splitting to H2-oxidizing microorganisms. To this end, hybrid biological-inorganic constructs have been created to use sunlight, air, and water as the only starting materials to accomplish carbon fixation in the form of biomass and liquid fuels. This artificial photosynthetic cycle begins with the Artificial Leaf, which accomplishes the solar process of natural photosynthesis-the splitting of water to hydrogen and oxygen using sunlight-under ambient conditions. To create the Artificial Leaf, an oxygen evolving complex of Photosystem II was mimicked, the most important property of which was the self-healing nature of the catalyst. Self-healing catalysts permit water splitting to be accomplished using any water source, which is the critical development for (1) the Artificial Leaf, as it allows for the facile interfacing of water splitting catalysis to materials such as silicon, and (2) the hybrid biological-inorganic construct, called the Bionic Leaf, as it allows for the facile interfacing of water splitting catalysis to bioorganisms. Hydrogenases in the bioorganism allow the hydrogen to be coupled to NADPH and ATP production, thus allowing the solar energy from water splitting to be converted into cellular energy to drive cellular biosynthesis. In the design of the hybrid system, water splitting catalysts must be designed that support hydrogen generation at low applied potential to ensure a high energy efficiency while avoiding reactive oxygen species. Using the tools of synthetic biology, a bioengineered bacterium, Ralstonia eutropha, converts carbon dioxide from air, along with the hydrogen produced from such catalysts of the Artificial Leaf, into biomass and liquid fuels, thus closing an entire artificial photosynthetic cycle. The Bionic Leaf operates at solar-to-biomass and solar-to-liquid fuels efficiencies that greatly exceed the highest solar-to-biomass efficiencies of natural photosynthesis.

In the context of a global artificial photosynthesis (GAP) project, we review our current work on nature's water splitting catalyst. In a recent report (Cox et al. 2014 Science 345, 804–808 (doi:10.1126/science.1254910)), we showed that the catalyst—a Mn4O5Ca cofactor—converts into an ‘activated’ form immediately prior to the O–O bond formation step. This activated state, which represents an all MnIV complex, is similar to the structure observed by X-ray crystallography but requires the coordination of an additional water molecule. Such a structure locates two oxygens, both derived from water, in close proximity, which probably come together to form the product O2 molecule. We speculate that formation of the activated catalyst state requires inherent structural flexibility. These features represent new design criteria for the development of biomimetic and bioinspired model systems for water splitting catalysts using first-row transition metals with the aim of delivering globally deployable artificial photosynthesis technologies.

This account deals with recent trends and challenges regarding photo(electro)chemical solar fuels produced by CO2 reduction and water splitting. The CO2 reduction process is limited by product sele...

… success of the artificial photosynthesis system undoubtedly … the water oxidation activity in an artificial photosynthesis system. … exploiting more efficient artificial photosynthesis system can …

The conversion of solar energy into chemical fuels can potentially address many of the energy and environment related challenges we face today. In this study, we have demonstrated a photochemical diode artificial photosynthesis system that can enable efficient, unassisted overall pure water splitting without using any sacrificial reagent. By precisely controlling charge carrier flow at the nanoscale, the wafer-level photochemical diode arrays exhibited solar-to-hydrogen efficiency ~3.3% in neutral (pH ~ 7.0) overall water splitting reaction. In part of the visible spectrum (400–485 nm), the energy conversion efficiency and apparent quantum yield reaches ~8.75% and ~20%, respectively, which are the highest values ever reported for one-step visible-light driven photocatalytic overall pure water splitting. The effective manipulation and control of charge carrier flow in nanostructured photocatalysts provides critical insight in achieving high efficiency artificial photosynthesis, including the efficient and selective reduction of CO2 to hydrocarbon fuels. A major challenge facing solar-to-fuel technologies is the integration of light-absorbing and catalytic components into efficient water-splitting devices. Here, the authors construct a photochemical diode array to harvest visible light and split pure water at high solar-to-hydrogen efficiencies.

… For light-to-chemical energy conversion as embodied in artificial photosynthesis, the splitting of water into its constituent elements is the key reaction, both energetically and …

… from sunlight-driven water splitting. Currently, research is … of water, together with a sacrificial electron acceptor or donor, respectively (Scheme 1C). The term “artificial photosynthesis”, …

… Although many of these alternative chemical solar energy systems are interesting, we focus here on the watersplitting reaction, because it effectively represents the scientific challenges …

The ongoing research and development of sunlight-driven water splitting in the “Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem)” is overviewed. Water splitting photocatalysts, photoelectrochemical devices, large-scale reactor panels, product gas transportation, H2/O2 gas separation devices and safety measures against explosion are included as the research objectives. ARPChem was formed as a research union of Japan’s leading chemical firms, in which related elementary technologies have been cultivated. This article introduces our general scope for artificial photosynthesis and describes present research activities, mainly on solar driven water splitting photocatalysts/photoelectrodes and briefly on the processes and plans for plant construction for future industrial extension.

… been studied as important components of artificial photosynthesis. This paper describes the … solar water splitting is discussed. Finally, a description of a possible artificial photosynthesis …

… of solar energy available to split water to produce dioxygen and the … This technology we will refer to as artificial photosynthesis. … of photosynthetic water splitting is further decreased. …

… Aiming at the significant improvement of the solar water splitting/artificial photosynthesis overall efficiency, attention should be focused for better fundamental knowledge of the …

… for light driven water splitting. Considering the catalytic water oxidation mechanisms of our … such a high photocurrent density on water splitting probably caused by the long flexible link …

… remains one of the focuses of the research on water splitting to hydrogen. … the artificial conjugated polymer only shows H 2 -producing activity from the half-reaction of water splitting, the …

Natural photosynthesis (NP) generates oxygen and carbohydrates from water and CO2 utilizing solar energy to nourish lives and balance CO2 levels. Following nature, artificial photosynthesis (AP), typically, overall water or CO2 splitting, produces fuels and chemicals from renewable energy. However, hydrogen evolution or CO2 reduction is inherently coupled with kinetically sluggish water oxidation, lowering efficiencies and raising safety concerns. Decoupled systems have thus emerged. In this review, we elaborate how decoupled artificial photosynthesis (DAP) evolves from NP and AP and unveil their distinct photoelectrochemical mechanisms in energy capture, transduction and conversion. Advances of AP and DAP are summarized in terms of photochemical (PC), photoelectrochemical (PEC), and photovoltaic-electrochemical (PV-EC) catalysis based on material and device design. The energy transduction process of DAP is emphasized. Challenges and perspectives on future researches are also presented.

Artificial photosynthesis has been devised and investigated in pursuit of solving 21th century's energy problem. Despite such advances in recent decades, applying the technology in real life is still a challenging subject for the scientists. As the term "artificial photosynthesis" stems from mimicking the natural photosynthesis, we can learn from the nature's strategies which have been evolved for 3.4 billion years. This review highlights important strategies of natural photosynthesis which can be borrowed for highly efficient and robust artificial photosystem for solar fuel production. Starting with a brief description of photosystem II in natural photosynthetic autotrophs, three relevant bioinspired strategies are discussed in this article: i) accumulative charge transfer, ii) photoprotection, and iii) self-healing. Then development of artificial photosystems mimicking those strategies will be discussed. Finally, remaining challenges and perspectives for future development of artificial photosynthesis are discussed.

… artificial photosynthesis and the use of the sun to drive solar fuel reactions for water splitting … by Honda and Fujishima on photoelectrochemical water splitting at TiO 2 with UV excitation. …

… the water splitting … artificial photosynthesis is dramatically reflected in the submissions we received for this themed issue: more than 2/3 of the papers deal with artificial photosynthesis…