Theoretical And Experimental Studies On Oxygen Evolution Reaction Of Surface Modified Ni₃Fe-LDHs

Among non-precious metal catalysts for electrochemical oxygen evolution reaction,NiFe-based catalysis has shown excellent performance.The research shows that the activity of the catalyst is closely related to the surrounding environment of the active site.In this paper,the overpotential of the metal site when the exposed surface(110)of Ni3Fe-LDHs is covered with different oxygen and sulfur atoms is calculated by density functional theory.The calculation results show that when the exposed surface is covered by 1/4 molecular layer of oxygen or sulfur,its overpotential is smaller.For the Fe site,the overpotentials when the 1/4 molecular layer is covered by oxygen/sulfur are 0.45 eV/0.153 eV,which are smaller than the overpotential of 0.57 eV on a clean surface.To explain the effect of oxygen/sulfur coverage on the performance,we further calculated the density of states and charge density.The density of states calculation results show that the oxygen/sulfur coverage will affect the electronic structure around the metal,and the charge density analysis shows that the electron of the metal site decreases,which is more conducive to the OH adsorption in the first step of the reaction.The application of phosphate-modified Ni3Fe-LDHs in water splitting was also studied.The effects of phosphate were studied by calculating the adsorption energy of intermediates and overpotential during oxygen evolution reaction when the(001)and(100)faces were modified with phosphate.The calculation results show that Ni3Fe-LDHs has better OER selectivity in the presence of phosphate.By analyzing the density of states,it is found that the phosphate will make the d-band center of the metal site closer to the Fermi level,and optimize the adsorption energy of the intermediate.The analysis of Gibbs free energy found that phosphate is a good proton acceptor,which can accelerate the decomposition of water in solutions and reduce the adsorption energy of OH to further improve the selectivity of OER.Ni3Fe-LDHs grown directly on CoPx nanowires were synthesized by hydrothermal and electrodeposition method,and the performance of OER were conducted and material structure is analyzed.The results show the presence of phosphate root on the surface of the material,which is beneficial to OER.The experimental and theoretical analysis results are consistent,which provides a new idea for the catalyst design of water splitting.