Preparation And Performance Of Polymetallic Transition Metal Sulfide Based Electrocatalysts For Oxygen Evolution Reaction

Electrochemical water splitting,as an efficient method to produce clean and green hydrogen energy,can effectively solve the problems of fossil energy shortage and environmental pollution.However,oxygen evolution reaction（OER）,which is generally considered to be the bottleneck of the water-splitting system due to the slow reaction kinetics caused by the four-electron transport mechanism,greatly limits the efficiency of water splitting.At present,noble metal oxides of Ru O₂ and Ir O₂ are used as commercial OER electrocatalysts due to their inherent high activity.However,the scarcity and high cost have severely hindered their large-scale industrial application.Therefore,it is of great significance to develop high-efficiency and low-cost non-precious metal electrocatalysts.In this thesis,several polymetallic transition metal sulfide-based electrocatalysts are prepared and characterized through various analysis techniques.Their electrocatalytic OER performances are systematically investigated,and the catalytic mechanisms are explored.The main research contents are as follows:1.Medium-entropy metal sulfides（MEMS）of（Ni Fe Co X）₃S₄（where X=Mn,Cr,Zn）are synthesized by a facile one-pot solvothermal strategy using molecular precursors.Benefiting from the low crystallinity and the multiple-metal synergistic effect,these MEMS catalysts show significantly enhanced electrocatalytic OER activity compared with the binary-metal（Ni Fe）₃S₄ and ternary-metal（Ni Fe Co）₃S₄counterparts.Especially,（Ni Fe Co Mn）₃S₄ delivers a low overpotential of 289 m V at 10m A cm^-2,a decent Tafel slope of 75.6 m V dec^-1,and robust catalytic stability in alkaline solution.Based on density functional theory（DFT）calculation and X-ray photoelectron spectroscopy（XPS）analysis,it is revealed that there is a synergistic effect between metal atoms in（Ni Fe Co Mn）₃S₄,resulting in the optimized electronic state to enhance electrocatalytic OER activity.This research paves a new route for the design,synthesis and practical application of medium-entropy sulfide electrocatalysts.2.A low crystallinity Fe-Co sulfide nanosheet modified with N-doped carbon dots（Fe Co S_y/NCDs）composite is prepared by a facile and mild one-pot solvothermal strategy.Benefitting from the low crystallinity and the synergistic effect between Fe Co S_y and NCDs,the optimal Fe Co S_y/NCDs-3 composite exhibits a low overpotential of 284 m V at 10 m A cm^-2,a decent Tafel slope of 52.1 m V dec^-1,and excellent electrochemical stability in alkaline solution.In addition,unlike ordinary metal sulfide electrocatalysts,the morphology,composition and structure of the Fe Co S_y/NCDs composite can be well retained after OER test.It is found that the introduction of NCDs can effectively increase the specific surface area of the catalyst and expose more catalytic active sites,and meanwhile enhance the electrical conductivity and promote electron transfer,thus boosting the electrocatalytic performance.This work provides a new approach for optimizing metal sulfide electrocatalysts.3.A V-doped polymetallic sulfide of V-（Co Fe Ni）S_y with porous hierarchical microsphere structure has been prepared on nickel foam（NF）by a simple two-step method.The V-doping not only changes the morphology of the catalyst and introduces more exposed active sites,but also optimizes the electronic structure and accelerates the electron transfer.Benefitting from the optimized electronic structure and the abundant catalytic active sites brought by the porous hierarchical microsphere structure,the V-（Co Fe Ni）S_y/NF electrode exhibits significantly improved electrocatalytic OER activity in alkaline media,showing a low overpotential of 186 and 239 m V at 10 and100 m A cm^-2,respectively,and an ultra-low Tafel slope of 16.5 m V dec^-1,as well as excellent electrochemical stability.This study provides a simple and effective method for the design and synthesis of high-performance V-doped OER electrocatalysts.