Research On The Structure Design And Performance Of Molybdenum Carbide As A Hydrogen Evolution Catalyst

The non-renewable nature of fossil fuels and the increasing consumption demand urge researchers to explore clean and renewable alternative energy source.Hydrogen energy has attracted much attention because of its high energy density and pollution-free characteristics.Water splitting employing renewable resource is considered to be the most promising technology.Platinum-group metals are currently the most effective electrocatalysts.However,due to their high prices and low reserves,they cannot be widely used.Therefore,it is an important way to realize the wide application of hydrogen energy to develop highly efficient HER electrocatalysts with low-cost to replace noble metal catalysts.In recent years,a large number of transition-metal-derived compounds with high reserves have attracted the interest of many researchers.Transition metal alloys,dichalcogenides,nitrides and carbides all exhibit high activity and stability for hydroelectric hydrogen resolution(HER).Among them,molybdenum carbide exhibits considerable catalytic activity compared with other molybdenum-based derivatives(sulfides,nitrides,etc.).Research suggests that molybdenum carbide has the similar band structure with Pt.Therefore,it has outstanding performance and is known as "platinum-like catalyst".In this paper,self-supporting catalytic electrode containing molybdenum carbide was prepared by simple in-situ carburization on synthesis.Mo-C@NF precursors were synthesized by using(NH4)6Mo7O24·4H2O as molybdenum source,glucose as carbon source and nickel foam as substrate.Mo2C@NF was prepared by high temperature in-situ carburizing,and a series of characterization of the materials were carried out.The results showed that the Mo2C@C materials contain ?-Mo2C,which were microspheric and uniformly distributed on the nickel foam(NF)framework.By changing the C-Mo ratio in the reactants,the temperature and atmosphere in the process of high temperature carbonization,it was found that the Mo2C@NF electrode had the best hydrogen catalytic properties in the C-Mo ratio of 20:1,850? and the mixture of hydrogen and nitrogen gas.It only need 42 mV can reach the current density of 10 mA·cm 2,and the Tafel slope is only 76 mV·dec-1.Compared with commercial platinum electrode,it had more beneficial hydrogen evolution performance.This is due to its better morphology,uniform dispersion of Mo2C nanoparticles resulting in larger specific surface area and more active sites.In order to further investigate the electrocatalytic performance of molybdenum carbide in electrolyte solutions with different pH values,we abandoned the method of directly adding nickel foam as collector to prepare self-supporting catalytic electrode.After preparing the fiber film containing Mo-PVP by Electrospinning technology,the Mo2C@CF self-supporting electrode constructed by carbon fiber cross-linked was obtained by high temperature carbonization.Mo-PVP fiber film was synthesized by electrospinning with(NH4)6Mo7O24·4H2O as molybdenum source,polyvinylpyrrolidone(PVP)as carbon source,water and N,N-dimethylformamide(DMF)as solvent.Then,Mo2C@CF was obtained by carburizing at 850?.XRD characterization shown that the main phase of molybdenum carbide in Mo2C?CF is ?-Mo2C.TEM images shown that this method can effectively avoid the aggregation of molybdenum carbide crystals.The electrochemical performance of Mo2C@CF electrode was tested.It was found that it exhibited an overpotential of 209 mV at the current density of 10 mA·cm-2 and the Tafel slope of 94 mV·dec-1 in acidic electrolyte.The catalytic performance of hydrogen evolution under alkaline conditions is better than that under acidic conditions.It yielded a current density of 10 mA·cm-2 at a relatively low overpotential(101 mV)and exhibit a low Tafel slope(63 mV·dec-1).