Preparation And Electrocatalytic Performance Of Metal Sulfide For Electrochemical N₂ Reduction Reaction

As an important chemical product,ammonia has been widely used in chemical intermediate,pharmaceutical intermediate,fertilizer and explosive.In addition,ammonia has attracted extensive attention with the advantage of high energy density and no carbon emission.At present,Haber-Bosch method is commonly adopted for the industrial ammonia synthesis,of which the reaction condition is greatly severe.What’s more,the waste water and gas produced in the synthesis process can easily bring great pollution to the environment.In comparison,electrocatalytic reduction of nitrogen to synthesize ammonia stands out in numerous ammonia synthesis paths because of its mild conditions,simple process,safety and controllability,which is considered to be one of the most promising methods for ammonia production.However,ammonia production rate and Faradic efficiency during the process of electrocatalytic NRR are relatively low,limiting its large-scale application.Therefore,it is of great significance to seek for high-efficiency,stable and cheap non-noble metal NRR electrocatalysts.In this paper,a series of catalysts with improved electrocatalytic NRR performance are prepared,and the electronic structure of the catalysts is regulated through the construction of heterojunction,defect engineering and transition metal atom modifying.The main research contents and experimental results are as follows:1.The construction of heterojunction between disulfides and the study of electrocatalytic NRR performance.The MoS₂/Ni₃S₂ catalyst has been in-situ assembled on Ni₃S₂ layer that grows on commercial Ni foam,with excellent charge transferring and enhanced catalytic activity.The successful construction of heterojunction not only improvs the charge transferring of MoS₂/Ni₃S₂,but also increases the electrochemical active areas for a large number of active sites,which boosts the electrocatalytic performance.The Faradaic Efficiency（FE）of NRR can reach 31.35%only at 0 V vs.RHE in neutral electrolyte.The results show that heterojunction plays an important role in enhancing catalytic activity of electrocatalyst.2.Regulating electronic structure of transition metal sulfide and enhancing electrocatalytic NRR performance through defect engineering.Sb₂S₃ with S vacancy（S_v-Sb₂S₃）is obtained by heat treatment of bulk Sb₂S₃ in reducing atmosphere.The results show that the introduction of S vacancy improves the conductivity of bulk Sb₂S₃and optimizes its electronic structure.Hence the electrocatalytic NRR performance of bulk Sb₂S₃ has been boosted.This work also uncovers the significance of defect engineering on the electronic structure and catalytic activity of catalysts,which provides an idea for the synthesis of low-cost and effective transition metal catalysts.3.Boosting the conductivity of metal sulfide through the modifying of transition metal atom and enhancing its electrocatalytic NRR performance.The electronic structure of the catalyst can be improved by the modification of metal atoms.In addition,the interaction between metal atoms and matrix can effectively boost the electrocatalytic properties of the material.Inspired from this,Ag-modifying S_v-Sb₂S₃（Ag-S_v-Sb₂S₃）has been synthesized through impregnation and subsequent calcination,during which the transition metal atom is anchored by sulfur vacancy.The successful modification of Ag enhances the conductivity of bulk Sb₂S₃,which promoted the charge transferring in the electrocatalytic NRR process,thus improving the NRR electrocatalytic activity of Sb₂S₃.