含有二价锡的水分解光阳极的光电化学稳定性研究

Photoelectrochemical (PEC) water splitting provides a cost-efficient means of solar hydrogen production with strategic application potential, and is currently facing the challenge of developing photoanodic materials with high efficiency and long-term stability operable at low applied bias, i.e., between 0.2~0.7 V vs.RHE. This project aims to investigate the potentials of Sn(II)-based ternary oxides as novel photoanodic materials for addressing the challenge above, by seeking possible solutions to the instability problem of these materials through rigorously studying the PEC surface corrosion process and its effect on the rapid decay of photoelectronic properties. Sn(II)-based oxides are an promising category of photoanodic semiconductors with narrower band gaps than conventional binary oxides and suitable band positions. However, due to the fact that Sn(II) tends to be easily oxidized and the difficulty of preparing electrodes, the application in photoelectrochemical water splitting is rarely reported. We will first attempt to develop efficient methods for materials and electrodes preparation, using tin niobate as an example, and then to study the mechanisms behind the PEC oxidation and corrosion process and to understand the accompanying surface changes in chemical compositions and crystal structures, and especially the determining factors for PEC property degradation, by developing suitable methods for photovoltage measurements in combination with various spectroscopic and PEC characterization methods. Based on the obtained insights, non-oxidative deposition techniques will be developed to deposit multi-purpose surface modifier or multi-layer coating materials with synergetic effect to improve the PEC properties and to reach a long-term stability of over 100 hours. The effect of the surface modifying layers on surface protection, charge transfer and PEC catalytic efficiency will be carefully studied to draw general principles for surface and interface engineering for this type of semiconductors.

光电解水制氢是一种具有战略应用潜力的低成本制氢技术，开发低偏压下具高效率长寿命的光阳极材料是该领域现阶段面临的重要挑战。本项目旨在发掘含有Sn(II)的三元氧化物作为新型阳极材料应对上述挑战的潜力，通过研究其光电化学腐蚀过程和光电性能衰减的关系，寻找解决稳定性难题的可行方案。此类半导体材料具有比传统氧化物更窄的能隙以及合适的平带电位，但是由于二价锡易被氧化以及电极制备方面的挑战，极少被报道用于光电解水制氢。我们将以铌酸锡为代表性材料，开发高品质合成和电极制备工艺，发展合适的光电压测试方法并结合多种光谱表征和光电化学分析手段，探究导致光电极氧化及腐蚀的机制和由此带来的表面化学组分和晶体结构的改变，分析电极光电性能衰减的关键因素。同时利用非氧化性沉积方法发展多功能单层修饰材料以及多层协同修饰材料，研究其对稳定性和光电性能的作用原理，总结设计依据，开发电极寿命100小时以上的高效铌酸锡光电极。

光电解水制氢是通过半导体材料将太阳能转化为化学能的过程，是解决未来能源问题和环境变化的途径之一。开发低偏压下高稳定性半导体材料仍面临巨大挑战。本项目重点研究以SnNb2O6为代表的二价锡材料作为水分解光阳极的潜力，并探究其合成条件对形貌特征，物理性质及光电性能的影响。通过研究二价锡表面光电腐蚀机理和性能衰减关系对其进行表面处理以提升其光电性能及稳定性并借助各种手段深剖其作用机理，以得到兼顾高性能，高稳定性及可重复性的光阳极。本项目执行顺利，圆满完成各项目标，具有较高的科学性和创新性。本项目取得的主要成果包括：1）通过低温熔盐法在氢气气氛中合成了氧缺陷高性能SnNb2O6片状材料，在1.23VRHE标准光谱AM1.5G牺牲剂存在情况下光电流密度达到3.1mA/cm2；2）熔盐法可控合成500nm-20um尺度的SnNb2O6片状单晶；3）光电腐蚀机理是由于表面二价锡氧化造成，从而造成性能及稳定性衰减；4）表面加载CoOx催化剂可有效提取空穴到表面进行氧化牺牲剂或水，进一步阻止了空穴不能导出而富集在表面对二价锡造成氧化；5）CoOx作为空穴提取层，NiOx作为产氧助催化剂具有高效的催化水分解能力，其光电流密度与催化氧化牺牲剂相当，在低偏压0.6VRHE下稳定性可以达到100小时以上。5）SnNb2O6光电催化性能具有温度依存性，温度上升带来该材料量子效率的进一步突破，1.23VRHE下量子效率超过60%，揭示了材料的导电性是效率的限制性因素之一；6）SnNb2O6表面二价锡氧化导致的光电腐蚀具有可逆性，在合适的溶液和电化学条件下，使氧化部分溶解从而暴露出未氧化部分，为以后光电极的循环利用和电极活化新方法奠定了基础；8）在铌酸亚锡光电极材料研究基础上拓展了其它亚锡基材料在光电催化水分解中的应用，并实现了效率突破。

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