Preparation Of Molybdenum Carbides And Electrocatalytic Performance In Water Splitting And Oxygen Reduction Reactions

The ever-increasing demands on traditional fossil fuels have stimulated considerable interests in renewable energy storage and conversion technology.The design and synthesis of cost-effective electrocatalysts with high activity and superior stability are crucial for water splitting and Zn-air battery.In this dissertation,Zeolitic Imidazolate Frameworks（ZIFs）were used as carbon source,nitrogen source and template,which were combined with molybdenum-based xoides and then carbonized at high temperature to form molybdenum-based carbide composite materials,and systematically studied the structure and electrocatalytic properties of the as-prepared materials.The main research contents of this dissertation are as follows.1.Nitrogen-doped molybdenum carbide mesocrystals were supported on carbon fiber paper（N-Mo₂C/CFP）as a self-supporting material for hydrogen evolution reaction（HER）under p H-universal conditions.Mo O₃·H₂O was readily coated on the surface of CFP by electrodeposition to form Mo O₃·H₂O/CFP.Mo O₃/CFP was obtained after dehydration.The topotactic transformation of Mo O₃/CFP in the presence of ZIF-67generated N-Mo₂C/CFP.The electrochemical deposition time,structure,morphology and element valence state of the as-prepared materials were well characterized by various test methods,and HER under p H-universal conditions were systematically studied.The results have demonstrated that the N-Mo₂C/CFP electrocatalyst electrochemically deposited for 45 min exhibits the excellent electrochemical activity,which only requires the overpotentials of only 45,80 and 37 m V to deliver the current density of 10 m A cm^-2in acidic,neutral and alkaline media,respectively.The free energy calculated by density functional theory also shows the excellent hydrogen evolution performance of N-Mo₂C/CFP.2.Ultra-thin molybdenum carbide（Mo₂C）nanosheets and cobalt（Co）and nitrogen（N）doped carbon polyhedron composite materials（Co@NC）were used for HER,oxygen evolution reaction（OER）and oxygen reduction reaction（ORR）.The introduction of molybdenum trioxide（Mo O₃）nanosheets during the synthesis of ZIF-67,and the precursor of Mo O₃/ZIF-67 was prepared by in-situ self-assembly.Subsequent pyrolysis under specific atmosphere gave rise to Mo₂C nanosheets on the surface of Co@NC polyhedron（Mo₂C/Co@NC）.The structure,microscopic morphology,specific surface area,and element valence state of the catalyst material were characterized by different test methods.HER,OER and ORR in the alkaline medium were studied systematically.In addition,it is also used as a cathode material for liquid metal research on zinc-air batteries.The research results have demonstrated that when compared with Mo₂C and Co@NC,the Mo₂C/Co@NC composite material can greatly improve the catalytic performance origin from the interface effect between Mo₂C and Co@NC,which improves the intrinsic activity to HER,OER and ORR.