Preparation Of Mo₂C-WC Materials And Study On Its Electrocatalytic Hydrogen Evolution Performance

In recent decades,human demand for energy has exploded,causing a drastically reduction in global fuels and environmental pollution.Faced with of energy crisis and environmental pollution,hydrogen has received widespread attention as an ideal clean energy.Electrocatalytic hydrogen evolution is an ideal way to obtain hydrogen energy,but catalysts are required to reduce the reaction overpotential.The ideal catalyst Pt is difficult to be widely promoted because of its low reserves and high price.Transition metal carbides represented by tungsten carbide（WC）and molybdenum carbide（Mo₂C）are regarded as potential substitutes for Pt due to their abundant reserves,low price,Pt-like electronic state structure and excellent electrocatalytic hydrogen evolution performance.In this thesis,starting from improving the electrocatalytic hydrogen evolution performance of WC and Mo₂C materials,using structural modulation and heterogeneous recombination,the Mo₂C-WC dual-phase composite materials with different structures are synthesized,and the influence of the introduction of the second phase on the electrocatalytic hydrogen evolution performance of the materials is studied.In this thesis,the Mo-AN rod template was formed by complexing ammonium molybdate and aniline,and two different Mo₂C-WC rod materials were prepared based on the preparation process of Mo-AN.The first is to directly introduce tungstic acid or phosphotungstic acid during the preparation of Mo-AN to obtain a rod structure,which is mainly composed of primary particles and has many pore structures.The second type is a three-dimensional rod（Mo₂C@WC/NRs-x）obtained by simultaneously introducing a carbon source and a molybdenum source to coat with Mo-AN.The specific structure is a three-dimensional composite rod structure with vertical nanosheets growing on a rod-shaped matrix.After optimization of the parameters,it is found that Mo₂C@WC/NRs needs 164 and 191 m V overpotentials to achieve 10 m A cm^-2 current density under acidic and alkaline conditions,respectively.After 11 h of i-t test,the material still has good catalytic stability.The performance of the Mo₂C@WC/NRs of the two structures is better than the single metal source WC/NRs and Mo₂C/NRs,indicating that the Mo₂C-WC heterostructure can improve the electrocatalytic hydrogen evolution performance of the single metal source tungsten carbide or molybdenum carbide.In the later stage,the Mo-W/PDA precursor is formed by complexing ammonium molybdate,ammonium tungstate and dopamine,and then the two-phase Mo₂C-WC is densely and uniformly confined in the ultra-thin carbon nanosheet assembly by in-situ pyrolysis of the polymer.Nanocrystals（Mo₂C-WC/NCAs）.Compared with single metal source WC/NCAs and Mo₂C/NCAs,Mo₂C-WC/NCAs only needs 126 m V overpotential to achieve 10 m A cm^-2 current density.Under acid and alkali conditions,the Tafel slope of Mo₂C-WC/NCAs They are 72 and 59 m V dec^-1 respectively.In addition,Mo₂C-WC/NCAs has excellent stability.After 36 h of stability test,it still has good catalytic performance.Density functional theory calculations show that the Mo₂C-WC structure can have a more suitable hydrogen adsorption free energy.The experimental performance and theoretical calculation together show that the heterostructure of dual-phase carbide（Mo₂C-WC）can improve the electronic structure of the catalyst and promote the charge transfer of the material,thereby improving the electrocatalytic hydrogen evolution performance of WC/NCAs or Mo₂C/NCAs.