Preparation And Electrocatalytic Performance For Water Splitting Of Transition Metal Chalcogenides

In order to meet the energy needs of modern society,people are still trying to find sustainable renewable and efficient clean energy.Hydrogen energy（H ₂）is an ideal clean chemical fuel and is considered as one of the most promising carbon-based fossil fuel alternatives due to its high energy density.Among various hydrogen production methods,electrochemical water splitting is an economical,environmentally friendly,and efficient method for hydrogen pro duction,which can be used to store intermittent renewable energy sources such as solar and tidal energy.Transition metal chalcogenides（TMC）have been extensively studied as effective substitutes for noble metal catalysts.Among the many ways to improve their catalytic performance,combining TMC with other materials to form composite structures is considered to be an effective way to improve electrocatalytic activity.This thesis mainly studies the water splitting catalytic activity of the synthesized com posite structural materials by synthesizing TMC composites,and explores the reasons for the improved catalytic performance.The specific research contents of this thesis are as follows:1.Among TMC,transition metal dichalcogenides（TMDs）have been widel y studied due to their excellent hydrogen evolution reaction（HER）performance.The integration of metal with TMDs is considered as one of the promising strategies to improve the HER performance of TMDs through modifying the electrocatalytic kinetics.However,the deposition of metal on TMDs often requires reducing agents,surfactants,or additional energy consumption,which increases the synthesis complexity and application cost.In this work,Cu was deposited on the Ni₃S₂nanomembranes grown in situ on a nickel foam substrate by a simple spontaneous substitution reaction of Cu²⁺and Ni at room temperature（Cu/Ni₃S₂/NF）.Microstructural characterization shows that Cu is uniformly distributed on the Ni ₃S₂nanomembranes in an amorphous state.The XPS test res ults show that the modification of Cu enriched electrons at the S site and depleted electrons at the Ni site.Electrochemical test results show that the Cu/Ni ₃S₂/NF electrode exhibits good electrocatalytic HER activity under alkaline conditions with an ons et potential(η₁₀)of only 130 mV.In addition,the Cu/Ni₃S₂/NF electrode also showed good electrocatalytic stability,with almost no increase in overpotential after continuous testing at a current density of-50 mA cm^-2 for 48 h.This work provides a conv enient method for metal-modified TMDs materials to prepare high-performance electrocatalysts and is expected to facilitate the application of TMDs in practical HER applications.2.Developing an efficient oxygen evolution reaction（OER）catalyst is an effective strategy for water electrolysis to achieve sustainable hydrogen energy production.Ni-based and Co-based selenides in TMC have attracted much attention due to their high electronic conductivity and excellent OER performance.The bimetallic selenides exhibit higher OER activity than single metal selenides due to the synergistic effect of Ni and Co.In this work,we used NiCo bimetallic selenide（Ni-Co-Se/NF）nanowires on nickel foam substrates for OER reaction.The catalyst was electrochemically tested to demonstrate higher OER activity than single Ni-Se/NF catalyst and Co-Se/NF catalyst.The as-prepared Ni-Co-Se/NF electrode can reach a current density of 50 mA cm^-2 at an overpotential of only 287 mV.Meanwhile,the electrochemical stability test showed that the current density of Ni-Co-Se/NF electrode did not decrease under the overpotential test of 300 mV for 24 h continuously.The XPS results prove that the high-valent metal oxides/hydroxides converted from Co during the OER test of the Ni-Co-Se/NF electrode are the actual active species.Such well-performing composites hold promise as OER catalysts to replace noble metals.