Theoretical Studies On Oxygen Evolution Performance And Mechanism Of TM-N-C Transition Metal Single-atom Catalysts

Water splitting technology is a critical renewable energy conversion method that involves the decomposition of water into hydrogen and oxygen,generating clean and sustainable hydrogen energy.However,the efficiency of hydrogen production through water electrolysis is limited by the high reaction potential and complex reaction process of the oxygen evolution reaction（OER）,which is a half-reaction of the electrolysis process.To address this issue,transition metal single-atom catalysts have emerged as a promising alternative to traditional precious metal catalysts,due to their comparable catalytic activity,low preparation cost,and excellent application potential in OER.In this thesis,the application of nitrogen-doped graphene-supported transition metal single-atom catalysts in OER was investigated,and the OER performance of various transition metal single-atom catalysts was theoretically investigated using density functional theory.Furthermore,the influence of axial oxygen-containing ligands on the catalytic activity of these catalysts was analyzed,laying a theoretical foundation for the design of highly active transition metal single-atom OER catalysts.This thesis focuses on nitrogen-doped graphene anchored Fe single-atom（Fe-N-C）catalysts,and determines that the most stable structure involves anchoring the transition metal single atom with four nitrogen atoms（TM-N₄-C）,with the Eley-Rideal mechanism being a reliable reaction pathway.Subsequently,the impact of axial oxygen-containing ligands on the oxygen evolution activity of Fe-N-C catalysts is investigated,along with an analysis of changes in the electronic structure of the active site before and after ligand adsorption.The results reveal that the adsorption of oxygen-containing ligands shifts the center of the dz² band of the active site metal atom closer to the Fermi level,thereby reducing the adsorption strength of reaction intermediates.This is identified as the main factor affecting the oxygen evolution activity of the catalyst.Further investigation of the oxygen evolution performance of other TM-N-C catalysts（Mn,Co,Ni,Cu）revealed that Co-N-C catalyst had the best catalytic activity(ΔG_max=1.562 e V)and moderate adsorption strength for the reaction intermediate*OH.Electronic structure analysis showed that the stronger the adsorption strength of the TM-N-C catalyst for the reaction intermediate,the more electrons were transferred from the active site.In this thesis,a systematic molecular orbital model was established,and the differential adsorption strength of*OH on different TM-N-C catalysts was explained by the bond order of*OH adsorption.Due to differences in the number of bonds,axial oxygen-containing ligand adsorption had different effects on the oxygen evolution activity of different TM-N-C catalysts.Axial oxygen-containing ligand could enhance the catalytic activity of Mn-N-C and Fe-N-C,but had a negative impact on Co-N-C.Through crystal orbital Hamiltonian population analysis and its integral results,we found that axial oxygen-containing ligand adsorption weakened the majority of TM-O bonds formed between most TM-N-C catalysts and the reaction intermediate,thereby reducing the adsorption strength and changing the oxygen evolution activity of the TM-N-C catalysts.The results of the theoretical calculations in this subject provide the necessary theoretical support for an in-depth understanding of the catalytic mechanism of highly active TM-N-C catalysts,as well as the experimental design and preparation of related transition metal single-atom catalysts.