BiVO4微纳结构光电极组合化学设计、构筑及其光解水制氢研究

Photoelectrochemical (PEC) water splitting for hydrogen production is a promising strategy for the capture and storage of the earth's abundant solar energy influx, through which intermittent unstorable solar energy can be converted into clean and storable hydrogen energy. This strategy provides a potential solution to the problems of energy shortage and environment pollution, and will benefit human for sustainable development. The greatest challenge in this field is developing efficient, stable and environment-friendly materials and devices to work under visible light irradiation for efficiency solar-hydrogen conversion. Ion doping, constructing heterojunction, surface modification and formation high efficient light-harvesting structures are four main methods to enhance the efficiency of photoelectrochemical solar-hydrogen conversion. BiVO4 is a potential material for solar-hydrogen photoelectrochemical conversion because of its non- toxicity, stable and appropriate band gap. Herein we propose the project, design and synthesis BiVO4-based micro/nano-structured photoanodes and their properties for hydrogen production from water splitting. In this project several BiVO4-based combinatorial materials libraries will be designed and synthesized with high-throughput by electrospray pyrolysis metal complex precursors, and then be rapid screened via scanning light absorption and photo-current measurements. By ion doping, construction heterojunction, surface modification and formation high efficient light-harvesting structures, we hope to improve electron mobility, promote the separation of photo-induced carriers and enhance the efficiency of photoelectrochemical hydrogen production. For the selected efficient lead materials we will investigate the crystal structure, morphology, energy band structure, optical absorption by XRD, SEM/TEM, PL, UV-vis etc and address microscopic understanding of their theoretical models regarding structural, optical, and electronic properties. Also photoelectrochemical properties for hydrogen production from water splitting will be systematically studied by Cyclic-Voltammetry (CV), photocurrent action spectroscopy, electrochemical impedance spectroscopy (EIS) and intensity modulated photocurrent spectroscopy (IMPS) for in-depth understanding of the effect and mechanism of charge carriers separation, migration in photoanodes and transfer at semiconductor/electrolyte interface. And these will rationally result in one or more efficient functional photoanodes for water splitting and all these investigations will provide useful theoretic and experimental supportings for their large scale manufacturing, industrial development and even pilot realization of solar-hydrogen systems.

研制和开发高效、稳定、环境友好的光解水材料和器件对解决能源短缺和环境污染两大问题具有重要的科学意义和实用价值。离子掺杂、构建异质结、表面修饰及形成高效捕光结构等是提高光解水效率的有效手段。本项目以具有可见光响应的BiVO4为研究对象，利用组合化学原理进行微纳结构光电极库的设计，采用金属络合物前驱液静电喷雾热分解进行高通量制备，通过扫描光学性能、光电流测试实现光解水材料的快速筛选；拟通过组合化学合成与传统单元合成相结合，建立和发展BiVO4微纳结构可控制备理论与工艺，揭示电极组成、结构、形貌与光解水产氢性能的关系；利用前述多种微纳结构促进光生电荷分离和传输，强化光生载流子利用，阐明其对提高光解水效率的作用机制，获得高活性光解水材料和器件；利用电化学分析、光电化学测试、光谱分析等手段揭示半导体/电解质界面反应过程机理及其动力学规律，为实现高效低成本太阳能制氢提供理论和技术支撑。

利用太阳能光解水制氢是根本性解决能源危机和清洁利用化石能源问题的理想方案。在光电化学分解水反应中,电极材料的性能是整个过程中的最大短板。本项目以BiVO4光电极为出发点，设计、构筑了一系列具有微纳结构的光电极，探究了结构设计与光解水性能的关系中诸多基础性的问题。首先，我们搭建了静电喷雾热分解薄膜材料制备平台，并在氟掺杂的氧化锡导电玻璃上成功制备出了纳米颗粒结构的BiVO4光电极。测试结果表明，在AM 1.5G模拟太阳光下，工作电位为1.9 V (相对于可逆氢电极) 时，光电流密度可至0.8 mA/cm2。在吸收谱内光电转换效率约为5%。过去的研究结果表明，电极表面的产氧反应是限制BiVO4光电极效率的最大短板。为了进一步提高BiVO4光电极的分解水制氢效率，我们提出了N2辅助静电喷雾热分解喷涂方案，成功的在多孔BiVO4表面均匀喷涂了薄层产氧助催化剂。值得注意的是，该喷涂过程可以在常压下进行，前驱液配置简单，具有良好的工业化推广前景。测试结果表明，喷涂Ni掺杂氧化钴后多孔BiVO4光电极具有更好的光解水制氢活性。工作电位在为1.23 V (相对于可逆氢电极) 时，电流密度可至2.6 mA/cm2。. 随后，我们采用多种化学合成方法合成了多种其他形貌结构的单一材质光电极： BiVO4纳米纤维光电极、WO3纳米纤维光电极、TiO2纳米纤维光电极、WO3纳米颗粒光电极、多孔WO3光电极等。光电化学测试结果表明，单一材料组成的纺丝纤维结构光电极在整体表现上并没有展现出优于其他微纳结构光电极。然而，以纺丝纤维结构为骨架的复合结构光电极却展现出非常优异的光电化学分解水性能。其中，核壳WO3/BiVO4 纳米纤维光电极在工作电极电位为1.9 V(相对于可逆氢电极)时，光电流密度可以达到1.75 mA/cm2。核壳TiO2/CdSe纳米纤维光电极的能量转换效率可至2.8%。最后，我们还成功的应用了第一性原理对光解水催化剂（BiVO4和锑锡二元金属氧化物）的晶体结构、能带结构进行了理论计算，进而促进了密度泛函理论在催化剂的设计与内在机理研究中的应用。