过渡金属水氧化催化剂结构与催化机理的理论研究

The development of efficient and stable water oxidation catalyst is crucial to improve the "Solar energy - fuel" conversion efficiency. In 2011, Sun Licheng et al reported a mononuclear Ru water oxidation catalyst that has by far the fastest catalytic rate, even comparable to the oxygen evolving complex in photosystem II in nature, among artificial water oxidation catalysts. However, the study of the "structure-property" relation and the reaction pathway at the microscopic level is still rather preliminary. The development of water oxidation catalysts based on the first row transition metals have economic advantages. In the past few years, Nocera et al reported the amorphous Co-oxo and Ni-oxo cluster systems which have good performance under mild conditions, i.e., room temperature and near neutral pH, and extraordinary self-healing capabilities. However, experiments such as in situ X-ray absorption spectroscopy only gave indirect information concerning the topology of the resting state and the activated state of the systems. The assignments of the oxidation states along the reaction pathway and the proposal of the key O-O bond formation transition state are also controversial. This project aims to find the root cause for the high efficiency and stability of the above Ru system and Co-oxo/Ni-oxo cluster systems by investigating systematically the reaction potential energy surface using the density functional theory and assigning accurately structural parameters based on combined quantum mechanics/experimental spectra refinement.

发展高效稳定的水氧化催化剂对提高“太阳能–燃料”转化效率至关重要。2011年，孙立成等报道了已知体系中速率最快的单核Ru水氧化催化剂，催化活性接近自然界光系统II中的放氧复合物。然而，对其“结构–性质”关系和反应历程的微观探索尚处于初步阶段。发展基于第一周期过渡金属的水氧化催化剂具有经济意义。近年来，Nocera等报道了基于Co–氧基和Ni–氧基的无定型簇合物体系，在室温和近pH中性的温和条件下有可观的反应速率和良好的自恢复特性。然而，原位X射线吸收光谱等实验只能给出关于Co–/Ni–氧基簇合物体系稳定态和活化态几何结构的间接数据，对于反应历程中体系氧化态的变化和关键O–O化学键生成步的研究也存在着争议。本项目针对上述Ru体系和Co–/Ni–氧基簇合物体系，使用密度泛函理论对催化反应势能面开展系统的研究，基于量子力学/实验谱联用精修，准确计算体系的结构参数，阐释催化剂高效稳定的内在驱动力。

本项目采用杂化密度泛函理论 B3LYP 研究了几种含第一周期过渡金属的水氧化催化剂的反应机理, 系统探索了体系在氧化过程中的电子结构变化, 阐释了关键的 O-O 过氧键成键步的机理. 结果表明, 两种含 Cu 的水氧化催化剂在生成过氧键时, 都将达到 Cu(III)-O• 形式氧化态. 含有未取代吡啶的 Cu 水氧化催化剂采取 O• 与 OH- 直接耦合的方式形成过氧键. 含有羟基取代基的 Cu 水氧化催化剂与光系统 II 更加类似, 采取 O• 与 O2- 直接耦合的方式形成过氧键. 而对于两种含 Co 的水氧化催化剂, Co(IV)-O• 是活性氧化态. 本项目同时研究了两种含有贵金属 Ru 的水氧化催化剂的反应机理. 最后, 本项目在微观水平研究了几种过渡金属酶蛋白体系的反应机理.