Theoretical Investigation Of Fe-based Water Oxidation Catalyst For Photocatalytic Oxygen Evolution

In the photocatalytic driven water decomposition technology,the oxygen generation step of water is always the key step of the whole reaction.In order to improve the efficiency of water decomposition,it is very important to develop a cheap,efficient and environment-friendly water oxidation catalyst.In this paper,we selected Fe(TPA)Cl2 and a pyridine substituted quinoline molecule in TPA as objects,and studied the catalysis of Fe(TPA)Cl2 and Fe(L)Cl2 by B3LYP-D3 functional of DFT.The geometry of Fe complexes with different valence states,the reference potential of oxidation reaction and proton coupling electron transfer reaction,and the change of Gibbs free energy of different reactions were calculated.Firstly,through the study of direct oxidation and ligand exchange reaction,it is determined that[Fe(TPA)Cl-H2O]+(1TPA)and[Fe(L)Cl-H2O]+(1)are the water oxidation catalysts in the subsequent catalytic cycle,and the ground state is quintuple.Then the catalytic cycle undergoes PCET,ion exchange and other processes,and the high spin reaction of metal Fe is most likely to occur.In the process of key oxygen oxygen bond formation,[Fe(X)(OH)=O...H2O]+(X=TPA?L)undergoes a five membered ring transition state with two intramolecular hydrogen bonds,which does not need the participation of proton coupling and electron transfer reaction,making the formation of oxygen bond simpler.Because the energy barrier formed by O-O bond in Fe(L)Cl2 system is 13.3kcal/mol higher than that of Fe(TPA)C12,the intermediate of Fe(?)complex with high oxidation state can be observed in the experiment,but the catalytic performance of Fe(L)Cl2 is weaker.Our theoretical calculation results explain that high valence Fe(?)intermediate can be observed in Fe(L)Cl2 system,but the activity of Fe(TPA)Cl2 and Fe(L)Cl2 catalysts for water oxidation still needs further study.