Preparation And Electrocatalytic Properties Of Transition Metal Carbide-Based Nanocomposites

As the energy crisis and environmental pollution problems become more and more serious,energy conversion and storage devices have been rapidly developed.The reactions mainly involve electrocatalytic hydrogen evolution reaction(HER),oxygen evolution reaction(OER),and oxygen reduction reaction(ORR).However,the high overpotential and sluggish kinetics greatly hindered their applications.By developing novel and efficient electrocatalysts can effectively reduce the reaction energy barrier and improve the reaction kinetics.At present,precious metal-based catalysts exhibit the best catalytic performance,but possess low reserves and high price.Therefore,reducing the amount of precious metals and developing transition metal-based catalysts with excellent performance have become the hotspot in the field of electrocatalysis.Transition metal carbide with Pt-like electron configuration is considered to be promising electrocatalytic materials.However,high temperature pyrolysis usually leads to large particle size,agglomeration and sintering of products,which reduce the catalytic performance.Therefore,it is of great significance to design and develop transition metal carbides with high performances and low price.Based on this,this thesis carries out the following research work:1.Nitrogen-doped carbon-wrapped iron carbide nanocomposites(Fe₃C@NPGL)were prepared by sacrificial template method together with g-C₃N₄ and dopamine as dual-nitrogen source.The presence of carbon layers can not only effectively avoid agglomeration of iron carbide nanoparticles,but also improve the activity and stability of catalysts through synergistic effects.XPS results showed that the nitrogen doping amount(8.86%)of Fe₃C@NPGL prepared by dual-nitrogen-source strategy was higher than that of g-C₃N₄(1.85%)or dopamine(2.23%)catalyst prepared by single nitrogen source.In addition,the graphitization degree of carbon layer will increase with the increase of carbonization temperature,but the nitrogen content will decrease.The electrocatalytic results showed that Fe₃C@NPGL exhibits a larger electrochemical active area,and the onset potential and half-wave potential were 1.05 V and 0.87 V,respectively,which were superior to commercial Pt/C catalyst.This work proves that the dual-nitrogen-source strategy can effectively improve the activity and stability of the catalyst.2.Cu embedded in Mo₂C octahedrons were prepared by pyrolyzing POMOFs.The existence of Cu can protect molybdenum carbide from being covered by excess carbon.Through acid etching of copper,pure phase of Mo₂C catalyst can be obtained.BET specific surface area results show that Mo₂C exhibits a larger specific surface area(251.12 m² g^-1),which is higher than that of Cu/Mo₂C(91.88 m² g^-1).When ruthenium supported on Mo₂C(Ru/Mo₂C),the overpotential is 52.6 m V at the current density of10 m A cm^-2 and Tafel slope of 40.1 m V dec^-1 in acidic medium.Moreover,the LSV curves of the catalyst did not deviate significantly before and after 10000 cycles,indicating Ru supported on molybdenum carbide could effectively improve HER performance of the catalyst.