基于非贵金属催化剂、无氧化还原电对的Z-scheme光解水体系的构建及反应机理研究

This project is directed against the fact that a non-precious metal based complex could not be employed as proton reduction catalyst in a light-absorbing semiconductor induced Z-scheme water splitting system and its efficiency is limited by the backward reaction of redox couples on the surface of semiconductor. In this view, a manganese porphyrin functioning as catalyst for two-electron water oxidation and a cobaloxime functioning as catalyst for proton reduction were covalently linked to two different photosensitizers, respectively. Photocatalytic olefin oxygenation with water as oxygen source could be coupled with photocatalytic proton reduction through the photoinduced electron transfer between the two molecular photosensitizers. In that way, a visible light driven Z-scheme water splitting system without redox couple was established based on supramolecular assemblies of non-precious metal catalysts linked to the photosensitizers. The research focused on the effect of the photoinduced electron transfer kinetics between photosensitizers and catalyst centers on the efficiency of the catalytic system, and to explore the working princible of the two photoreaction units coupled in one pot system through electron transfer, providing new ideas for the development of highly efficient Z-scheme water splitting system for hydrogen production without sacrificial electron donor.

针对以半导体为光捕获剂的Z-scheme光解水制氢体系中无法使用非贵金属配合物作为产氢催化剂、氧化还原电对在半导体表面的逆反应制约体系效率的问题，本项目将活化水分子发生双电子氧化的卟啉锰和具有催化质子还原功能的丁二酮肟钴分别与两个不同的光敏剂通过共价键连接，通过两个分子光敏剂之间的光诱导电子转移，实现以水为氧源的烯烃光催化氧化与光催化质子还原在同一反应体系中耦合。采用非贵金属催化剂与光敏剂连接构成的超分子组装体，构建不含氧化还原电对的Z-scheme光分解水体系。着重讨论光敏剂与催化中心的光诱导电子转移动力学对体系催化性能的影响，探索两个光反应单元通过电子转移在同一体系中耦合的规律，为建立不含电子牺牲剂的高效Z-scheme光解水制氢体系提供新的思路。

高效利用波长范围400-700 nm内的可见光驱动分解水，是实现太阳能制氢的关键。本项目针对目前水氧化光阳极无法有效利用500nm以上可见光的问题，构建了以卟啉锡为光敏剂，联吡啶Ru配合物为分子水平水氧化催化剂的水氧化光阳极，依靠卟啉光敏剂的Q带吸收500 nm以上的可见光实现水氧化。在此基础上，模拟光合作用体系II中酪氨酸的功能，在光阳极中引入含有酚羟基的二级电子给体M，促进光敏剂再生、抑制光生电荷复合，从而提高了光阳极分解水的法拉第效率。鉴于分子光敏剂在反应过程中稳定性较差，开展了半导体光敏剂与分子催化剂相结合的水氧化光阳极构建。以WO3/BiVO4复合光阳极表面负载卟啉镍催化剂，表明了卟啉镍在光阳极表面促进光生空穴向水中注入的功能，在低偏压（0.6 V vs. RHE）下达到45%的空穴注入效率。并以能带位置与BiVO4相似的TiO2与WO3构成复合光阳极，通过瞬态光伏技术，阐明了光阳极内部光生电荷传输机制，并考察了卟啉镍在光阳极表面脱落的原因。进而在BiVO4光阳极表面引入富含氧空位的ZnO作为空穴传输层，并以ZnO为平台生长卟啉镍的MOF骨架结构，并证明ZnO中的氧空位可以将BiVO4中的光生空穴转移给MOF催化剂。此外，发展了能够吸收500-700nm可见光的p型CuO光阴极，并在表面制备NiS催化剂，提高了光阴极的稳定性，可与BiVO4光阳极构成Tandem串联光电化学池，实现光阳极与光阴极在不同波长下分别产氧、产氢。