Perovskite Oxide Based Electrodes for High‐Performance Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is an attractive strategy for the large‐scale production of renewable hydrogen from water. Developing cost‐effective, active and stable semiconducting photoelectrodes is extremely important for achieving PEC water splitting with high solar‐to‐hydrogen efficiency. Perovskite oxides as a large family of semiconducting metal oxides are extensively investigated as electrodes in PEC water splitting owing to their abundance, high (photo)electrochemical stability, compositional and structural flexibility allowing the achievement of high electrocatalytic activity, superior sunlight absorption capability and precise control and tuning of band gaps and band edges. In this review, the research progress in the design, development, and application of perovskite oxides in PEC water splitting is summarized, with a special emphasis placed on understanding the relationship between the composition/structure and (photo)electrochemical activity.     

High-performance potassium poly(heptazine imide) films for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is an appealing approach by which to convert solar energy into hydrogen fuel. Polymeric semiconductors have recently attracted intense interest of many scientists for PEC water splitting. The crystallinity of polymer films is regarded as the main factor that determines the conversion efficiency. Herein, potassium poly(heptazine) imide (K-PHI) films with improved crystallinity were in situ prepared on a conductive substrate as a photoanode for solar-driven water splitting. A remarkable photocurrent density of ca. 0.80 mA cm⁻² was achieved under air mass 1.5 global illumination without the use of any sacrificial agent, a performance that is ca. 20 times higher than that of the photoanode in an amorphous state, and higher than those of other related polymeric photoanodes. The boosted performance can be attributed to improved charge transfer, which has been investigated using steady state and operando approaches. This work elucidates the pivotal importance of the crystallinity of conjugated polymer semiconductors for PEC water splitting and other advanced photocatalytic applications.

Potassium poly(heptazine imide) photoanode is synthesized, and owing to the improved crystallinity, it has presented a remarkable performance for solar-driven water splitting.     

硫氧键合BiVO4光阳极与FeNi催化剂实现高效水氧化

光电催化分解水可以将充足的太阳能直接转化存储为绿色清洁的氢能,然而光阳极表面缓慢的析氧反应动力学严重限制了太阳能到氢能的转化效率。我们通过一种简单的S-O键合策略实现BiVO4光阳极与FeNi催化剂的界面耦合（S:BiVO4-FeNi）,其光电催化分解水的光电流达到6.43 mA/cm2（1.23 VRHE, AM 1.5G）。进一步研究结果表明：界面S-O键合能够有效实现BiVO4光阳极光生电荷分离并促进空穴向FeNi催化剂表面迁移。同时,S-O键合可以进一步调控FeNi催化剂表面的电荷分布,从而有效提高光电化学分解水析氧活性和稳定性。该工作为设计构建具有高效、稳定的太阳能光电催化分解水体系提供了一种新的研究策略。     

PEC films prepared from Chitosan-Alginate coacervates

Chitosan-alginate polyelectrolyte complex (PEC) have been prepared in situ in beads and microspheres. This study examines the preparation of suitable chitosan-alginate coacervates for casting into homogeneous PEC films for potential applications in packaging, controlled release systems and wound dressings. Coacervation between chitosan and alginate was rapid, but the rate may be controlled with the addition of water miscible organic solvents. Compared with ethanol and PEG200, acetone was the more promising solvent moderator. Suspensions of fine, uniformly dispersed coacervates were produced by a dropwise addition of 0.25% w/v chitosan solution (solvent: 1: 1 v/v of 2% acetic acid and acetone) into 0.25% w/v sodium alginate solution in water under rapid agitation. The PEC films were transparent and flexible. They exhibited high permeability to water vapor, but resisted complete dissolution in 0.1 M HCI, distilled water and pH 7.4 phosphate buffer solution. Microscopic heterogeneity in the films could be reduced by immersion in aqueous media, but this was accompanied by modifications in the thickness, permeability and mechanical property of the films.     

Emerging materials for plasmon-assisted photoelectrochemical water splitting

Energy production and environmental pollution are the two major problems the world is facing today. The depletion of fossil fuels and the emission of harmful gases into the atmosphere leads to the research on clean and renewable energy sources. In this context, hydrogen is considered an ideal fuel to meet global energy needs. Presently, hydrogen is produced from fossil fuels. However, the most desirable way is from clean and renewable energy sources, like water and sunlight. Sunlight is an abundant energy source for energy harvesting and utilization. Recent studies reveal that photoelectrochemical (PEC) water splitting has promise for solar to hydrogen (STH) conversion over the widely tested photocatalytic approach since hydrogen and oxygen gases can be quantified easily in PEC. For designing light-absorbing materials, semiconductors are the primary choice that undergoes excitation upon solar light irradiation to produce excitons (electron-hole pairs) to drive the electrolysis. Visible light active semiconductors are attractive to achieve high solar to chemical fuel conversion. However, pure semiconductor materials are far from practical applications because of charge carrier recombination, poor light-harvesting, and electrode degradation. Various heteronanostructures by the integration of metal plasmons overcome these issues. The incorporation of metal plasmons gained significance for improving the PEC water splitting performance. This review summarizes the possible main mechanisms such as plasmon-induced resonance energy transfer (PIRET), hot electron injection (HEI), and light scatting/trapping. It also deliberates the rational design of plasmonic structures for PEC water splitting. Furthermore, this review highlights the advantages of plasmonic metal-supported photoelectrodes for PEC water splitting.     

提高氧化铁光电催化分解水效率的策略进展

为了解决能源危机与环境污染问题,发展一种可再生的清洁能源至关重要.太阳能是一种取之不尽用之不竭的清洁能源,而氢气是一种良好的能源载体.利用太阳能光电催化水分解制氢,是一项有望能够解决能源与环境问题的技术,具有很大的应用前景.其中,氧化铁因为具有合适的能带位置与带隙、良好的稳定性与廉价无毒等优点,成为一种理想的光阳极材料...     

Electrochromic and photoelectrochromic properties of sol–gel derived tungsten trioxide/titania composite thin films

Tungsten trixoide/titania (WO₃-titania) composite thin films with W/Ti molar ratios of 100/0, 98/2, 96/4, 94/6 92/8 and 90/10 were prepared on fluorine-doped tin oxide conducting glass, and their electrochromic (EC) and photoelectrochromic (PEC) performances were investigated in this study. The composite thin films were synthesized by sol–gel process using peroxotungstic acid and titanium (IV) n-butoxide as the precursors. The surface morphology and composition of the composite thin films were characterized using scanning electron microscope with energy dispersive spectrometer. Electrochemical experiments with in situ spectroscopic measurement were employed to study the EC properties of the composite thin films. It was found that the presence of titania in the WO₃ matrix might slightly decreases its EC performance. PEC cells using the composite thin films as the working electrode and a sputtered semitransparent platinum thin film on ITO as the counter electrode were fabricated and their PEC performances were investigated. The device using composite thin film prepared from sol solution with a W/Ti molar ratio of 96/4 exhibited the best PEC performance.     

Near infrared-driven photoelectrochemical water splitting: Review and future prospects

Photoelectrochemical (PEC) water splitting supplies an environmentally friendly, sustainable approach to generating renewable hydrogen fuels. Oxides semiconductors, e.g. TiO₂, BiVO₄, and Fe₂O₃, have been widely developed as photoelectrodes to demonstrate the utility in PEC systems. Even though significant effort has been made to increase the PEC efficiency, these materials are still far from practical applications. The main issue of metal oxides is the wide bandgap energy that hinders effective photons harvesting from sunlight. In solar spectrum, over 40% of the energy is located in the near-infrared (NIR) region. Developing sophisticated PEC systems that can be driven by NIR illumination is therefore essential. This review gives a concise overview on PEC systems based on the use of NIR-driven photoelectrodes. Promising candidates as efficient yet practical NIR-responsive photoelectrodes are suggested and discussed. Future outlooks on the advancement of PEC water splitting are also proposed.     

Recent advances in bismuth vanadate-based photocatalysts for photoelectrochemical water splitting

Photoelectrochemical(PEC) technology is considered to be a promising approach for solar-driven hydrogen production with zero emissions. Bismuth vanadate(BiVO_4) is a kind of photocatalytic material with strong photoactivity in the visible light region and appropriate band gap for PEC water splitting.However, the solar-to-hydrogen efficiency(STH) of BiVO_4 is far away from the 10% target needed for practical application due to its poor charge separation ability. Therefore, this review attempts to summarize the strategies for improving the photocurrent density and especially hydrogen production of BiVO_4 materials through PEC techniques in the last three years, such as doping nonmetal and metal elements, depositing noble metals, constructing heterojunctions, coupling with carbon and metalorganic framework(MOF) materials to further enhance the PEC performance of BiVO_4 photoanode. This review aims to serve as a general guideline to fabricate highly efficient BiVO_4-based materials for PEC water splitting.     

Hematite/Si nanowire dual-absorber system for photoelectrochemical water splitting at low applied potentials

Hematite (α-Fe(2)O(3)) was grown on vertically aligned Si nanowires (NWs) using atomic layer deposition to form a dual-absorber system. Si NWs absorb photons that are transparent to hematite (600 nm < λ < 1100 nm) and convert the energy into additional photovoltage to assist photoelectrochemical (PEC) water splitting by hematite. Compared with hematite-only photoelectrodes, those with Si NWs exhibited a photocurrent turn-on potential as low as 0.6 V vs RHE. This result represents one of the lowest turn-on potentials observed for hematite-based PEC water splitting systems. It addresses a critical challenge of using hematite for PEC water splitting, namely, the fact that the band-edge positions are too positive for high-efficiency water splitting.     

BiVO4/CuBi2O4薄膜光电极的制备及光电性能

通过金属有机物分解法(MOD)协同光电化学沉积法, 将p型氧化物半导体CuBi₂O₄沉积在BiVO₄纳米薄膜上, 形成包覆性异质结结构, 制备了一种新型p-n异质结光阳极n-BiVO₄/p-CuBi₂O₄, 用于太阳能光电化学(Photoelectrochemical, PEC)水分解. 研究结果表明, 在1.23 V(vs. RHE)电势下, BiVO₄/CuBi₂O₄ 异质结光阳极表现出优良的PEC水氧化性能, 光电流密度达到2.8 mA/cm², 负载磷酸钴(Co-Pi)的BiVO₄/CuBi₂O₄/Co-Pi光电极, 光电流密度达到4.45 mA/cm², 分别为BiVO₄电极光电流密度的3.1倍和4.9倍. X射线衍射(XRD)、 紫外-可见吸收光谱(UV-Vis)、 电化学阻抗谱(EIS)和能级结构图等结果也证实, BiVO₄/CuBi₂O₄和BiVO₄/CuBi₂O₄/Co-Pi复合电极材料在内建电场和能带弯曲作用下, 光吸收特性增强, 载流子界面转移电阻减小, 具有良好的光电化学性能与稳定性.     

A BiVO4 Photoanode with a VOx Layer Bearing Oxygen Vacancies Offers Improved Charge Transfer and Oxygen Evolution Kinetics in Photoelectrochemical Water Splitting

Sluggish oxygen evolution kinetics are one of the key limitations of bismuth vanadate (BiVO₄) photoanodes for efficient photoelectrochemical (PEC) water splitting. To address this issue, we report a vanadium oxide (VO_x) with enriched oxygen vacancies conformally grown on BiVO₄ photoanodes by a simple photo-assisted electrodeposition process. The optimized BiVO₄/VO_x photoanode exhibits a photocurrent density of 6.29 mA cm⁻² at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination, which is ca. 385 % as high as that of its pristine counterpart. A high charge-transfer efficiency of 96 % is achieved and stable PEC water splitting is realized, with a photocurrent retention rate of 88.3 % upon 40 h of testing. The excellent PEC performance is attributed to the presence of oxygen vacancies in VO_x that forms undercoordinated sites, which strengthen the adsorption of water molecules onto the active sites and promote charge transfer during the oxygen evolution reaction. This work demonstrates the potential of vanadium-based catalysts for PEC water oxidation.     

光电催化用于高附加值化学品合成

化石燃料的过度消耗导致了能源短缺和环境破坏,因此可再生清洁能源的开发已成为当务之急.在众多可再生能源中,太阳能因其环境友好,储量巨大且分布广泛等特点而引起了研究者们的兴趣.光电催化(PEC)是一种能够将可再生太阳能转化为化学能的方法,而最受关注的是通过PEC水分解来获得高附加值的氢能源.欲使PEC系统实现水分解,理论上...     

Research Progress of Ferrite Materials for Photoelectrochemical Water Splitting

Photoelectrochemical(PEC)water splitting is an effective strategy to convert solar energy into clean and renewable hydrogen energy.In order to carry out effective PEC conversion,researchers have conducted a lot of exploration and developed a variety of semiconductors suitable for PEC water splitting.Among them,metal oxides stand out due to their higher stability.Compared with traditional oxide semiconductors,ferrite-based photoelectrodes have the advantages of low cost,small band gap,and good stability.Interestingly,due to the unique characteristics of ferrite,most of them have various tunable features,which will be more conducive to the development of efficient PEC electrode.However,this complex metal oxide is also troubled by severe charge recombination and low carrier transport efficiency,resulting in lower conversion efficiency compared to theoretical value.Based on this,this article reviews the structure,preparation methods,characteristics and modification strategies of various common ferrites.In addition,we analyzed the future research direction of ferrite for PEC water splitting,and looked forward to the development of more efficient catalysts.     

Developing high-quality g-C3N4 film electrode for the photoelectrocatalytic degradation of methylene blue in water

Developing a high-quality photoelectrode for photoelectrochemical applications is still an ongoing challenge. In this study, we prepared the g-C₃N₄ film on the indium tin oxide (ITO) glass through conventional coating, liquid-based growth, in-situ calcination, and vapor deposition methods, respectively. These electrodes were characterized and used as photoanodes to degrade methylene blue (MB) in water. Among these methods, the in-situ calcination method was most appropriate for preparing the continuous and organized g-C₃N₄ film electrodes with uniform g-C₃N₄ coverage and strong adhesion to the ITO substrate. It also had the highest activity in the photocatalytic (PC), electrochemical (EC), and photoelectrocatalytic (PEC) degradation processes of MB. In the PEC reaction, at an applied potential of 1.0 V and a light intensity of 0.96 W/cm², the removal rate of MB was 62.5%, which was much higher than those in the PC and EC reactions. The high degradation rate was due to the synergistic effect of PEC degradation, wherein the PC and EC reactions promote and optimize each other. In the PC reaction, MB was degraded by ?CH₃ elimination, while the EC degradation pathway mainly included the conversion of sulfhydryl into sulfoxide and the opening of the central aromatic ring. Both methyl loss and aromatic ring opening occurred in the PEC reaction. Moreover, some monocyclic compounds were formed, and MB showed more complete degradation in the PEC reaction.     

TiO_2纳米阵列光阳极光电催化水分解研究进展

光电催化水分解制氢是目前解决能源危机与环境污染最理想的技术之一.设计和构筑高效的光阳极是实现光电催化技术实际应用的关键.在众多半导体光阳极材料中,TiO_2纳米阵列由于其快的电荷传输速率,高的光热稳定性,无毒和成本低等优点,已经被广泛用于光电催化水分解反应的研究.但是TiO_2本征的光吸收范围窄、光生电荷复合率高、表面水氧化动力学缓慢严重地制约了其太阳能-氢能转换效率.我们结合近年来国内外及本课题组的研究工作详细论述了TiO_2纳米阵列的改性策略,主要包括利用元素掺杂来拓展TiO_2的光吸收范围并提高导电性,构筑异质结促进光电极电荷的分离与转移,半导体敏化增加光电极的可见光吸收并促进电荷转移,表面处理用于增加表面水氧化反应速率.最后指出了该材料发展现状,并对其发展前景做出展望.我们为进一步提高TiO_2纳米阵列的光电催化水分解活性提供了理论指导和实践借鉴.     

Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting

Nanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro-architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze-casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm⁻² before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm⁻² and an accordingly high incident photon-to-current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance.     

硫化钴装饰BiVO4光阳极提升其光电化学水分解性能

太阳能驱动的光电化学(PEC)水分解可以有效地将太阳能转化为化学能,作为解决环境排放和能源危机最具前景的途径之一,已经引起了科学界的广泛关注.PEC水分解系统由两个半反应组成:在光阳极上的析氧反应(OER)和光阴极上的析氢反应(HER).PEC系统的太阳能转化效率主要由光阳极/电解质界面的OER过程所决定,这是一个非常复杂且涉及质子偶联的多步四电子转移过程.钒酸铋(BiVO₄)是应用于PEC水分解的典型且具有实际应用前景的光阳极材料之一.然而,由于不良的表面电荷转移、电荷在光阳极/电解质结面处的表面复合以及缓慢的OER动力学等因素,导致BiVO₄的PEC性能受到严重限制.本文开发了一种新颖有效的解决方案,以低成本、高电导率和具有快速电荷转移能力的硫化钴装饰来提升BiVO₄光阳极的PEC活性,X射线多晶衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征,研究结果表明CoS成功装饰于BiVO₄表面.采用紫外-可见吸收光谱(UV-VisDRS)研究了BiVO₄和复合光阳极CoS/BiVO₄的光学性质,结果表明,与纯的BiVO₄相比,CoS/BiVO₄光阳极在可见光范围内光吸收能力有所增强.将制备的BiVO₄和CoS/BiVO₄光阳极应用于PEC分解水实验中,结果表明,相对于1.23 V可逆氢电极,在光照下,CoS/BiVO₄光阳极的光电流密度显著提升,可高达3.2 m Acm^-2,是纯BiVO₄的2.5倍以上.与纯BiVO₄相比,CoS/BiVO₄光阳极的起始氧化电位显示出负向偏移0.2 V,表明析氧过电势得到有效减小.入射光子转换效率(IPCE)测试结果表明,CoS/BiVO₄光阳极的入射光子转换效率在500 nm之前的可见光范围内得到明显提升,其中,CoS/BiVO₄的IPCE值在380 nm处达到最大.此外,由于CoS的装饰作用,CoS/BiVO₄光阳极的电荷注入效率和电荷分离效率均得到较大的提升,分别达到75.8%(相较于纯BiVO₄光阳极的36.7%)和79.8%(相较于纯BiVO₄光阳极的66.8%).电化学阻抗谱(EIS)测试结果表明,通过CoS的装饰,CoS/BiVO₄光阳极的界面电荷转移电阻得到有效降低,证明其界面电荷转移动力学得到有效提升.光致发光光谱测试结果表明,CoS的装饰显著提高了BiVO₄的光生电子-空穴对的分离效率,进一步证明BiVO₄表面的CoS装饰在其PEC分解水中起着非常积极的作用.本文为通过表面修饰设计应用于PEC水分解的有效的光阳极提供了新思路.     

Cobalt oxide and carbon modified hematite nanorod arrays for improved photoelectrochemical water splitting

Given the proper band gap, low cost and good stability, hematite(α-Fe_2O_3) has been considered as a promising candidate for photoelectrochemical(PEC) water splitting, however suffers from the sluggish surface water oxidation reaction kinetics. In this study, a simple dip-coating process was used to modify the surface of α-Fe_2O_3 nanorod arrays with cobalt oxide(CoO_x) and carbon(C) for the improved PEC performance, with a photocurrent density at 1.6 V(vs. reversible hydrogen electrode, RHE) increased from 0.10 mA/cm~2 for the pristine α-Fe_2O_3 to 0.37 mA/cm~2 for the CoO_x/C modified α-Fe_2O_3 nanorods. As revealed by electrochemical analysis, thanks to the synergistic effect of CoO_x and C, the PEC enhancement could be attributed to the enhanced charge transfer ability, decreased surface charge recombination, and accelerated water oxidation reaction kinetics. This study serves as a good example for improving PEC water splitting performance via a simple method.     

太阳能分解水制氢最近进展:光催化、光电催化及光伏-光电耦合途径

能源是人类生存和发展的物质基础,太阳能作为最丰富的清洁可再生能源之一,其开发利用受到了世界范围内的广泛关注.通过光催化分解水制氢将太阳能以化学能的形式储存起来不仅能利用太阳能制取高燃烧值的氢能,同时氢能可与CO2综合利用结合起来,在减少碳排放的同时,生成高附加值的化学品,实现碳氢资源的优化利用.光催化分解水制氢在过去的几年里取得了长足的进步,本综述从三种研究广泛的太阳能光催化分解水制氢途径(即光催化、光电催化以及光伏-光电耦合途径)入手,分别简要介绍了太阳能分解水制氢在近几年取得的最新研究进展.利用纳米粒子悬浮体系进行光催化分解水制氢成本低廉、易于规模化放大,被认为是未来应用最可行的方式之一,但是太阳能转化利用效率还偏低.最新报道的SrTiO3:La,Rh/Au/BiVO4:Mo光催化剂其太阳能到氢能(STH)转化效率已超过了1.0%,相比之前报道的大多数光催化剂体系有了数量级的飞跃,让人们对太阳能光催化分解水制氢未来的规模化应用看到了希望.高效宽光谱响应的光催化剂、高效电荷分离策略、新型高效助催化剂以及气体分离新方法和新材料等,均是粉末光催化剂体系研究最为关键的问题;光电催化分解水在过去2–3年内发展迅速,在一些典型的光阳极半导体材料(如BiVO4和Ta3N5等)体系上太阳能利用效率超过2.0%以上.最新研究发现,在Ta3N5光阳极的研究中,通过在光电极表面合理设计和构筑空穴传输层和电子阻挡层等策略,光电流和电极稳定性均可得到大幅度提升,光电流大小甚至可接近Ta3N5材料的理论极限电流.如果能进一步在过电位和电极稳定性上取得突破,该体系的STH转化效率还会得到大幅度改进.此外,光阴极的研究也越来越受到了研究者的关注;光伏-光电耦合体系在三种途径里面太阳能制氢效率最高,在多个体系上已超过10%以上,最近报道的利用多结GaInP/GaAs/Ge电池与Ni电催化剂耦合,其太阳能制氢效率可达到22.4%.虽然该种制氢途径的效率已超过其工业化应用的要求,但是光伏电池的成本(尤其是多结GaAs太阳电池)极大限制了其大面积规模化应用,同时还要考虑电催化剂的成本和效率等,光伏-光电耦合制氢是成本最高的太阳能制氢途径.需要指出的是,光伏-光电耦合制氢有望在一些特殊的领域最先取得实际应用,如为外太空航天器、远洋航海以及孤立海岛等传统能源无法满足的地方提供能源供给.总之,太阳能分解水制氢研究取得了一系列重要进展,太阳能制氢效率得到了大幅度提升,也是目前世界范围内关注的研究热点之一,不仅具有强的潜在工业应用背景,更为基础科学提供了诸多新的研究课题.这一极具挑战的研究领域,在先进技术快速发展和基础科学问题认识不断提高的基础上,不久的将来,有望在不久的将来在基础科学和应用研究方面取得重大突破.