Theoretical Study On Catalytic Mechanism Of Ru Carboxyl Complex/Co DMA Complex In Water Oxidation

With the shortage of fossil fuels and the increasingly serious environmental pollution,the solar energy as the ultimate energy source of the earth has attracted increasing attention.Artificial photosynthesis can use solar energy to decompose H2O into H2 and O2.The splitting reaction of water molecule includes water oxidation half reaction and proton reduction half reaction.Water oxidation reaction is considered as the bottleneck of water splitting for its high overpotential and kinetic energy barrier.Therefore,the development of water oxidation catalyst?WOCs?with excellent performance is essential to achieve efficient water splitting.The oxygen evolution complex?OEC?in the natural photosynthetic system?PSII?provides an idea for the design of efficient water oxidation catalysts.However,the complex structure of amino acid ligands and Mn clusters in OEC makes the synthesis of OEC very difficult.The WOCs with simple structure,low overpotential,large number of turnover,high turnover rate were synthesized by using proton acceptor ligands,such as the ligand containing carboxylic instead of amino acid ligand and mononuclear or dinuclear transition metal atoms instead of Mn cluster.The catalytic activity of the catalyst can be improved by modifying the ligand or changing the spatial structure of the ligand.Based on quantum chemistry methods,the influence of ligands on catalytic performance and the mechanism of catalysts can be investigated,which provide theoretical guidance for the design of excellent performance catalysts.This thesis consists of four chapters.The first chapter mainly introduces the classification of water oxidation reaction and the development of water oxidation catalysts.The second chapter mainly introduces density functional theory?DFT?and transition state theory.The third and fourth chapters are the main contents of this thesis,which are as follows:1.Ru-based water oxidation catalyst[LRu^II]⁺?L=5,5-chelated 2-carboxy-phen,2,2';6',2''-terpyridine?was studied by density functional theory.The oxidation activation reaction of catalyst,O?O bond formation and oxygen release process are studied.The results show that the intramolecular oxidizing ligands?carboxyl?can be used as proton receptors in the catalytic process of water oxidation,which can improve the whole catalytic cycle.Therefore,the intramolecular proton receptor can be used as a ligand of WOCs for the design and synthesis of efficient catalysts.2.Co-based water oxidation catalyst[L^HCo^II?CH₃CN?₂]⁺?a?and[L^DMACo^II?CH₃CN?₂]⁺?b??L=N,N?-dimethyl-N,N?-bis?2-pyridylmethyl?ethane-1,2-diamine;DMA=dimethylamine?were studied by density functional theory calculations.The oxidation activation reaction of catalyst and O?O bond formation were studied.The results show that the water bridge in the reaction has slightly influence on the reaction energy barrier,which is related to the steric hindrance caused by the spatial structure of the system.The ligands as proton receptors significantly effect on the energy barrier of O?O bond formation.Therefore,ligand can be used as a proton receptor to effectively improve the activity of water oxidation catalyst.