Preparation And Study Of Cobalt-based Electrocatalyst For Hydrogen Evolution Reaction

In recent years the problems of fossil energy depletion and the increasing environmental pollution are becoming more and more serious problems,it is imperative to develop sustainable clean energy source.Hydrogen as a potential sustainable and clean energy has always attracted much attention because of high burning value,clean and pollution-free,and abundant resources.Water electrocatalysis technology is a simple and feasible method for preparing high-purity hydrogen,but the hydrogen evolution reaction on the cathode is limited by the hydrogen evolution kinetics.Therefore,it is necessary to develop a high-efficiency catalyst electrode to accelerate hydrogen evolution reaction.The noble metal Pt is considered to be the most efficient hydrogen evolution catalyst,but the low reserves and high cost limit its wide application in the field of mass production of hydrogen by water splitting.Therefore,it is very urgent to develop non-precious electrocatalysts with high hydrogen evolution performance.Transition metal cobalt based electrocatalyst is a promising candidate due to its high reserves,low cost and high activity.This thesis focuses on the development of cobalt-based composite catalysts,and investigate its hydrogen evolution performance.The main work of this thesis is as follows:1.In this chapter,anodized amorphous TiO₂ nanotube arrays were used as templates to prepare Co_x P nanoparticles embedded in N-doped TiO₂ nanotube arrays by hydrothermal reaction,thermal treatment in ammonia and phosphating treatment.This unique nanostructure of Co_xP nanoparticles embedded in N-doped TiO₂ nanotubes not only maintained the structural stability,but also provided a fast electron channel for hydrogen evolution reaction through N-doped TiO₂ nanotube wall,which reducing the electron transfer impedance as well as the fast transport of electrolyte ion and hydrogen bubble diffusion.By studying the different phosphating temperature,it was found that Co_xP/N-TiO₂ NTAs with best catalytic performance canbe obtained when phosphating temperature is 300℃,the corresponding electrocatalysis shows low overpotential of 180mV at a current density of 10 mA/cm² with dynamics Tafel slope of 51 mV/dec,as well as long cycle stability.2.In this chapter,ZnCo₂O₄ nanosheet was grown on the nickel foam by simple hydrothermal method,and then ZnCo₂O₄ nanosheet was reduced by hydrogen gas and decomposed to form Co/ZnO hybrid structure wth original nanosheet shape.The composite electrode exhibites low electron contact resistance,and amount of hydrogen evolution reaction active sites.The three-dimensional connected pore structure and the special structure of vertically oriented nanosheet are beneficial to bubble extraction and electrolyte transport.The catalytic results showed that the composite structure has excellent catalytic activity in 1 M KOH electrolyte and exhibits low overvpotential of-137 mV at a current density of 10 mA/cm² as well as high stability without potential decline for 7 hours at a current density of 10 mA/cm².3.In this chapter,precursor of ZnCo₂O₄ nanosheet on nickel foam was obtained through hydrothermal reaction,and porous flake Co_xN/ZnO nanosheet was further obtained through therlmal treatment in ammonia.The composite material forms with Co_xN as a conductive skeleton for core,and the ZnO shell is coated on the Co_xN surface layer.This unique structure not only increases the reaction area of the catalyst but also accelerates electron transport and bubble diffusion,moreover the synergistic action of Co_xN/ZnO enhances the catalytic activity.In alkaline conditions,only overvpotential of63 mV is reached at a current density 10 mA/cm²,and after continuous hydrogen evolution for 10 h,only 18 mV overpotential shift was observed.