Investigation On Electrocatalytic Performance Of Transition Metal Composite Nitrogen-doped Carbon Materials

Hydrogen energy is considered as as the most ideal substitute for fossil energy because of wide sources,high combustion efficiency and pollution-free.Electrochemical water splitting,is a kind of hydrogen energy preparation method with the advantages of abundant raw materials,simple operation and environmental friendliness,which has a wide application prospect.Transition metals have the advantages of abundant reserves,low cost,and excellent performance.Nitrogen-doped carbon materials possess outstanding electrical conductivity,easily adjustable electronic properties and favorable stability.In this paper,a series of efficient and stable electrocatalysts for hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）were prepared by combining transition metal and nitrogen-doped carbon materials through reasonable design.By means of various characterization methods and catalytic performance tests,the catalytic mechanism and active components of the catalyst were explored,providing a feasible route for the preparation of highly active non-precious metal catalysts.The details are listed as follows:（1）A series of Mo and N co-doped carbon materials（Mo/NC-T）were prepared by ion exchange method and high temperature pyrolysis using metal organic framework as precursors.The as-synthesized Mo/NC-T samples exhibited superior electrocatalytic OER properties,and he sample obtained from pyrolysis at 650℃（Mo/NC-650）presented the best OER catalytic performance and stability.In 1 M KOH electrolyte,it just required a low overpotential of 320 m V to reach a current density of10 m A cm^-2,and the corresponding Tafel slope was 71 m V dec^-1.It was found that the presence of abundant Mo³⁺and pyridinic N in Mo/NC-650acted as the active sites for OER,and carbon material as substrate improved the oxidation resistance and accelerated the charge transfer.Therefore,the synergistic effect of various factors jointly promoted the improvement of OER performance.（2）A series of nitrogen-doped carbon-coated Ni₃Mo₃N porous microrods grown on Ni foam（Ni₃Mo₃N-NC/NF）were synthesized by hydrothermal reaction and high-temperature pyrolysis.It was found that Ni₃Mo₃N-NC/NF catalysts possessed moderate hydrogen adsorption capacity due to the interaction between Ni and Mo.In addition,the morphology of three-dimensional porous microrod array increased the surface area and accelerated gas evolution,and the coating of nitrogen-doped carbon enhanced conductivity and oxidation resistance of the catalyst.HER test results showed that the HER performance of Ni₃Mo₃N-NC/NF is much better than that of single-metal nitride.It just required a small overpotential of 39 m V to reach a current density of 10m A cm^-2,and the corresponding Tafel slope is 77 m V dec^-1,which is superior to most reported metal nitride catalysts.Compared with most metal nitrides previously reported,the material showed excellent HER catalytic activity,excellent stability and oxidation resistance.This paper includes 40 figures,8 tables and 139 references.