In-Situ Construction Of Multicomponent Heterogeneous Catalyst For Oxygen Evolution Performance

Hydrogen energy is the reliable clean energy to solve the energy crisis and environmental pollution.Water electrolysis technology is a typical new technology for green hydrogen production and expected to replace fossil hudeogen production.However,the water electrolysis process is limited to the anodic oxygen evolution reaction（OER）which undergoes a four-electron transfer process,so catalyst is needed.Transition metal oxide-based electrocatalysts have become the focus of scientific researchers due to their low price,abundant reserves and easy structure regulation.Multi-component transition metal oxides with heterogeneous interfaces can effectively improve the disadvantages of single structure and low catalytic activity of traditional single-component transition metal oxide catalysts by utilizing the synergistic effect and phase interface effect between components.However,the current preparation of heterojunction catalysts focuses on the layer-by-layer stacking method,and the active layer is easily detached during the oxygen evolution catalytic process,which affects the catalytic activity and structural stability of the electrode.Therefore,rational design of composite oxygen evolution catalysts with close contact between phase and phase interface and exploration of their mechanism of action have become the focus of research.Based on the thermodynamic instability of solid solution oxides,this paper proposes to prepare supersaturated solid solution oxide precursors by adjusting element composition and combining rapid self-propagating combustion technology.The decomposition of precursors was promoted by hydrogen thermal reduction,and the oxygen vacancies and nanoscale contact heterojunction were introduced in one step to increase the electrocatalytic activity and conductivity,and finally the controllable construction of high-efficiency heterojunction oxygen evolution catalysts were realized.The specific work is as follows:1)Construction of Co Fe₂O₄/Ni O heterojunction catalytic and study on catalytic performance for oxygen evolution.Ni-supported rock salt phase Fe Co Ni O_x solid solution oxide precursor（SNCF）was obtained by self-propagating solution combustion method using iron nitrate,nickel nitrate,cobalt nitrate and glycine as raw materials and nickel foam as matrix.By regulating the hydrogen reduction process,nanoporous heterojunction electrocatalysts with different compositions were successfully obtained.Through the characterization of morphology and phase structure,the thermodynamic influence mechanism of the solid solution oxide decomposition under reducing atmosphere was clarified.The oxygen evolution electrochemical tests of different samples showed that Co Fe₂O₄/Ni O heterojunction catalyst（R-SNCF4.5）had the best oxygen evolution catalytic efficiency.At the current densities of 10 m A·cm^-2 and 100 m A·cm^-2,only 231m V and 331 m V overpotentials were required,and the stability was maintained for more than 80 h.The total water splitting system assembled with R-SNCF4.5 and commercial Pt/C as anode and cathode achieved alkaline total water splitting at 1.51 V(10 m A·cm^-2).Further DFT calculations showed that the Co Fe₂O₄/Ni O heterojunction effectively adjusted the*OOH binding energy and hydrogen desorption energy,reducing the energy barrier in the OER process.Theoretical calculations proved that Fe can be used as an active site,and the presence of Ni and Co improved the conductivity of the electrode.2)The construction and oxygen evolution catalytic performance of high entropy alloy/oxide heterojunctions.In order to further strengthen the high catalytic effect of the heterogeneous interface and improve the conductivity,in this experiment,five different nitrates and glycine were used as the main raw materials,and different systems of alloy/oxide dual-phase heterogeneous structure electrodes were prepared by self-propagating solution combustion method and hydrogen thermal reduction method.The effects of element composition and reduction temperature on the phase,morphology and catalytic performance of the electrode were investigated.XRD showed that Fe Co Ni Cu/Fe Co Ni Cu Mn O_x and Fe Co Ni Cu/Fe Co Ni Cu Al O_x heterostructure electrodes（R-SNCFCM4.5 and R-SNCFCA4.5）were formed at 450℃.It was found that R-SNCFCA4.5 had excellent oxygen evolution catalytic performance.The overpotential of R-SNCFCA4.5 electrode was 228 m V at 10 m A·cm^-2.The cyclic test also showed that the R-SNCFCA4.5 electrode had excellent catalytic stability.This is mainly because R-SNCFCA4.5 contain abundant conductor/semiconductor heterogeneous interfaces,suitable vacancy concentration and pore structure,thereby improving the catalytic oxygen evolution performance.