α-Fe_2O_3光阳极光电化学分解水的研究进展与挑战

近年来,光电化学分解水制氢(PEC)技术为未来的能源需求提供了一个清洁、可再生的途径.赤铁矿(α-Fe_2O_3)因其带隙小(～2.1 eV)、无毒、存储量大以及光电化学稳定等优点而受到广泛关注.然而,导电性差、空穴扩散长度短(2～4 nm)、表面水氧化动力学缓慢、激发态寿命短(10×10~(-12) sec)等缺点,极大地限制了Fe_2O_3光阳极的光转换效率.我们回顾了赤铁矿光阳极用于PEC水氧化的研究进展,主要集中在促进Fe_2O_3光阳极表面的水氧化反应,体相的电荷分离和迁移以及提高光吸收能力.最后,对Fe_2O_3光阳极面临的挑战和未来的发展进行了展望.     

Ti和乳酸共改性α-Fe2O3光阳极光电化学性能研究

采用一步水热后在氮气中进行热处理的方法制备了Ti和乳酸共改性的纳米花状α-Fe₂O₃光阳极。对样品分别进行了X射线衍射、扫描电镜、X射线光电子能谱、紫外-可见吸收光谱和光电化学性能测试。与乳酸改性的纳米片状α-Fe₂O₃光阳极相比,最优的Ti与乳酸共改性样品0.075LA-Fe2O3-0.75Ti光阳极的光电流密度从0.55mA·cm^-2提高到1.39mA·cm^-2。Ti改性明显减少了0.075LA-Fe₂O₃膜的表面态,增加了表面载流子注入效率;同时Ti的掺入也增加了电极体内载流子浓度,增强了体内载流子的传输效率。     

光电化学分解水电池的电极性能提高方法及光阴极研究进展

光电化学水分解电池能够将太阳能直接转化为氢能,是一种理想的太阳能利用方式. p-n叠层电池具有理论转换效率高、成本低廉、材料选择灵活等优势,被认为是最有潜力的一类光电化学水分解电池. 然而,目前这类叠层电池的太阳能转化效率还不高,主要原因是单个电极的效率太低. 本文介绍了几种提高光电极分解水性能的方法--减小光生载流子的体相复合、表面复合以及抑制背反应等,同时综述了国内外关于几种p型半导体光阴极的研究进展,如Si、InP、CuIn_1-x GaxS(Se)₂、Cu₂ZnSnS₄等. 通过总结,作者提出一种p-Cu₂ZnSnS₄(CuIn_1-xGaxS(Se)₂)/n-Ta₃N₅(Fe₂O₃) 组装方式,有望获得高效低成本叠层光电化学水分解电池.     

光电催化分解水的光阳极改性策略

Photoelectrochemical water splitting is to utilize collected photo-generated carrier for direct water cleavage for hydrogen production. It is a system combining photoconversion and energy storage since converted solar energy is stored as high energy-density hydrogen gas. According to intrinsic properties and band bending situation of a photoelectrode, hydrogen tends to be released at photocathode while oxygen at photoanode. In a tandem photoelectrochemical chemical cell, current passing through one electrode must equals that through another and electrode with lower conversion rate will limit efficiency of the whole device. Therefore, it is also of research interest to look into the common strategies for enhancing the conversion rate at photoanode. Although up to 15% of solar-to-hydrogen efficiency can be estimated according to some semiconductor for solar assisted water splitting, practical conversion ability of state-of-the-art photoanode has yet to approach that theoretical limit. Five major steps happen in a full water splitting reaction at a semiconductor surface:light harvesting with electron excitations, separated electron-hole pairs transferring to two opposite ends due to band bending, electron/hole injection through semiconductor-electrolyte interface into water, recombination process and mass transfer of products/reactants. They are closely related to different proposed parameters for solar water splitting evaluation and this review will first help to give a fast glance at those evaluation parameters and then summarize on several major adopted strategies towards high-efficiency oxygen evolution at photoanode surface. Those strategies and thereby optimized evaluation parameter are shown, in order to disclose the importance of modifying different steps for a photoanode with enhanced output.     

尖晶石型铁酸盐的制备和表征研究

本文采用空气氧化湿法制备尖晶石铁酸盐，得到最佳生成条件为：Ｒ－２ＯＨ＾－／（Ｍ＾２＋＋Ｆ２＋）≥１．０；Ｍ＾２＋／Ｆｅ＾２＋＝０．５摩尔比；氧化温度３４３－３５８Ｋ；氧化时间１０－２５小时。通过ＸＲＤ、ＴＰＲ和ＴＰＤ等方法对其进行表征，讨论了尖晶石型铁酸盐的氧化－还原活及其化学组成和结构的变化。     

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.     

结合光电化学和瞬态吸收光谱技术研究光电化学分解水载流子动力学

半导体光电化学制氢是一种重要的、有前景的太阳能应用技术. 其产氢效率取决于光生载流子的产生、分离和传输效率. 深入理解光生载流子的动力学过程对于设计高效的太阳能产氢器件有重要的指导意义. 光电化学和瞬态吸收光谱技术是研究光催化反应微观动力学和机理的强有力手段. 本文介绍作者应用这些技术在半导体光电化学制氢方面所取得的部分最新研究结果, 并对存在的问题和今后研究重点提出了一些看法.     

尖晶石型铁酸盐纳米晶制备技术的研究进展

综述了尖晶石型铁酸盐纳米晶制备技术的研究进展,介绍了高能球磨法、聚合物热解法、自蔓延燃烧合成法、共沉淀法、水热法、溶胶-凝胶法、微乳液法等典型制备技术的作用原理和技术特点,并对尖晶石型铁酸盐纳米晶制备技术的发展趋势进行了展望。     

尖晶石型铁酸盐的制备及表征研究

本文采用空气氧化的湿法制备了尖晶石型铁酸盐，得到最佳生成条件为：在空气流速为２００ｍｌ／ｍｉｎ和配料比Ｒ＝２ＯＨ－／（Ｍ２＋＋Ｆｅ２＋）≥１．０，Ｍ２＋／Ｆｅ２＋＝０．５（摩尔比）下氧化温度和时间分别为３４３－３５８Ｋ和１０－２５ｈ。使用ＸＲＤ、ＴＰＲ和ＴＰＤ等方法对所制备的铁酸盐进行了表征，研究了其结构特征及氧化－还原活性，并讨论了该活性与化学组成及结构的关系。     

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.     

Photoelectrochemical and Photovoltaic Characteristics of Amorphous‐Silicon‐Based Tandem Cells as Photocathodes for Water Splitting

In this study amorphous silicon tandem solar cells are successfully utilized as photoelectrodes in a photoelectrochemical cell for water electrolysis. The tandem cells are modified with various amounts of platinum and are combined with a ruthenium oxide counter electrode. In a two‐electrode arrangement this system is capable of splitting water without external bias with a short‐circuit current of 4.50 mA cm^?2. On the assumption that no faradaic losses occur, a solar‐to‐hydrogen efficiency of 5.54 % is achieved. In order to identify the relevant loss processes, additional three‐electrode measurements were performed for each involved half‐cell.     

Epitaxial Cubic Silicon Carbide Photocathodes for Visible-Light-Driven Water Splitting

Cubic silicon carbide (3C-SiC) material feature a suitable bandgap and high resistance to photocorrosion. Thus, it has been emerged as a promising semiconductor for hydrogen evolution. Here, the relationship between the photoelectrochemical properties and the microstructures of different SiC materials is demonstrated. For visible-light-derived water splitting to hydrogen production, nanocrystalline, microcrystalline and epitaxial (001) 3C-SiC films are applied as the photocathodes. The epitaxial 3C-SiC film presents the highest photoelectrochemical activity for hydrogen evolution, because of its perfect (001) orientation, high phase purity, low resistance, and negative conduction band energy level. This finding offers a strategy to design SiC-based photocathodes with superior photoelectrochemical performances.     

Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells

Hydrogenases (H₂ases) are benchmark electrocatalysts for H₂ production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p‐type Si photocathode for optimal loading and wiring of H₂ase through the introduction of a hierarchical inverse opal (IO) TiO₂ interlayer. This proton‐reducing Si|IO‐TiO₂|H₂ase photocathode is capable of driving overall water splitting in combination with a photoanode. We demonstrate unassisted (bias‐free) water splitting by wiring Si|IO‐TiO₂|H₂ase to a modified BiVO₄ photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si|IO‐TiO₂|H₂ase to a photosystem II (PSII) photoanode provides proof of concept for an engineered Z‐scheme that replaces the non‐complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode.     

Facet Engineering on WO3 Mono-Particle-Layer Electrode for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) performance of WO₃ photoanodes for water splitting is heavily influenced by the orientation of crystal facets. In this work, mono-particle-layer electrodes, assembled by particulate WO₃ square plates with highly uniform alignment along the (002) facet, improved PEC water oxidation kinetics and stability. Photo-deposition of Au along the cracks formed on the surface of the plates, which are the edges of {110} facets, was found to further enhance electron collection efficiency. Combination of these two strategies allowed the facet-engineered WO₃ electrode to produce significantly higher efficiencies in charge separation and transfer than the electrode prepared without facet orientation. This work has provided a facile route for fabricating a structurally designed WO₃ photoelectrode, which is also applicable to other regularly shaped semiconductor photocatalysts with anisotropic charge migration.     

Spatially Separated Photosystem II and a Silicon Photoelectrochemical Cell for Overall Water Splitting: A Natural–Artificial Photosynthetic Hybrid

Integrating natural and artificial photosynthetic platforms is an important approach to developing solar‐driven hybrid systems with exceptional function over the individual components. A natural–artificial photosynthetic hybrid platform is formed by wiring photosystem II (PSII) and a platinum‐decorated silicon photoelectrochemical (PEC) cell in a tandem manner based on a photocatalytic‐PEC Z‐scheme design. Although the individual components cannot achieve overall water splitting, the hybrid platform demonstrated the capability of unassisted solar‐driven overall water splitting. Moreover, H₂ and O₂ evolution can be separated in this system, which is ascribed to the functionality afforded by the unconventional Z‐scheme design. Furthermore, the tandem configuration and the spatial separation between PSII and artificial components provide more opportunities to develop efficient natural–artificial hybrid photosynthesis systems.     

A Semiconductor-Mediator-Catalyst Artificial Photosynthetic System for Photoelectrochemical Water Oxidation

In fabricating an artificial photosynthesis (AP) electrode for water oxidation, we have devised a semiconductor-mediator-catalyst structure that mimics photosystem II (PSII). It is based on a surface layer of vertically grown nanorods of Fe₂O₃ on fluorine doped tin oxide (FTO) electrodes with a carbazole mediator base and a Ru(II) carbene complex on a nanolayer of TiO₂ as a water oxidation co-catalyst. The resulting hybrid assembly, FTO|Fe₂O₃|−carbazole|TiO₂|−Ru(carbene) , demonstrates an enhanced photoelectrochemical (PEC) water oxidation performance compared to an electrode without the added carbaozle base with an increase in photocurrent density of 2.2-fold at 0.95 V vs. NHE and a negatively shifted onset potential of 500 mV. The enhanced PEC performance is attributable to carbazole mediator accelerated interfacial hole transfer from Fe₂O₃ to the Ru(II) carbene co-catalyst, with an improved effective surface area for the water oxidation reaction and reduced charge transfer resistance.     

Fluorine‐Doped Porous Single‐Crystal Rutile TiO2 Nanorods for Enhancing Photoelectrochemical Water Splitting

Fluorine‐doped hierarchical porous single‐crystal rutile TiO₂ nanorods have been synthesized through a silica template method, in which F^? ions acts as both n‐type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F‐doped porous single crystals displays a remarkably enhanced solar‐to‐hydrogen conversion efficiency (≈0.35 % at ?0.33 V vs. Ag/AgCl) under 100 mW cm^?2 of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO₂ single crystals.