Controlled Synthesis,Structural Modulation And Hydrogen Evolution Property Of Molybdenum Carbide/Sulfide/Phosphide Electrocatalysts

With the rapid comsuption of coal-,oil-,and natural gas-based fossile energies,more and more people are desiring the development of clear energies,which are believed to be the alternatvies of conventional fossile energies.Hydrogen,owing to its high energy density and environmental benign,has attracted much research attention and is considered as a robust condidate for future energy uses.At present,researchers are attempting to acquire the hygrogen energy via a hydrogen evolution process through electrocatalytic decomposion of H₂O using excessive electricity generated by solar cell,wind,and tidal power generation.As such,highly efficient electrocatalysts for hydrogen evolution reaction are urgently needed for pushing forward the practical application of electrocatalytic hydrogen generation.Noble metal Pt are currently used as a commercial avaiblable electrocatalyst.However,in consideration of its high price and limited production,the large-scale application of Pt electrocatalyst is practially impossible.Transition metal molybdenum?Mo?is abundant and relatively cheaper and has good chemical stability and,thus,attracts much research attention for its use as electrocatalysts in hydrogen evolution reaction.Many researches have been attempted to construct Mo-based electrocatalysts with controlled structure and multifunctionality for improving their hydrogen evolution property.Meanwhile,the studies have also tried to modulate the conductivity and electrocatalytic behavior through complexion,hybridization and doping.However,until now,the controlled synthesis and structural modulation of Mo-based electrocatalysts still are the big challenges.Accouting for the above research background,this thesis aims to develop unique synthetic strategies for controlled synthesis of three-dimensional hybrid or doped type molybdenum phosphide/nitrogen-doped carbon?MoP/C-N?,molybdenum carbide/nitrogen-doped carbon?Mo_xC/C-N?,and vanadium-doped molybdenum sulfide nanoelectrocatalysts.The composition,structure,size and morphology,surface area and porous structure,and surface elemental composition and valence state are investigated systematically and the hydrogen evolution property is also studied.The results show that the hydrogen evoltion property of molybdenu-based electrocatalysts is largely colerrated to their compsiiton and structure.Thus,through modulating the synthesis and structures,the optimizatin of molybdenu-based electrocatalysts can be realized.The obtained molybdenu-based electrocatalysts show great potential for applications in hydrogen generation.The detailed research contents are listed below:1.Three-dimensional porous MoP/C-N hybrid electrocatalysts were prepared by evaporating the precursor mixture containing SiO₂ spheres dissolved in H₂O as templates,cyanoguanidine,ammonium molybdate and diammonium hydrogen phosphate as precursors,which was subjected to the phosphatization treatment under high temperature followed with removal of SiO₂ with HF.The composition,structure,size and morphology,surface elemental composition and valence state of the obtained hybrid electrocatalyst were characterized by a variety of techniques and their hydrogen evolution property was evaluated.2.Three-dimensinal porous Mo_xC/C-N hybrid electrocatalysts were synthesized via ionothermal synthesis using ammonium molybdate as Mo source,ammonium chloride as an ionothermal agent,cyanoguanidine as both nitrogen and carbon sources.Through modulating the amounts of ammonium molybdate and cyanoguanidine during the synthesis,the structure,size and morphology,and electrochemical property can be modulated.When the molar ratios of ammonium molybdate and cyanoguanidine was set at 1:1,the synthesized Mo₂C/C-N hybrid electrocatalysts possess the optimum hydrogen evolution performance with an initial overpotential of 6 mV and a overpotential of 98 mV at a current density of 10mA·cm^-2,showing the superior perforamce over most previously reported Mo₂C electrocatalysts.3.Three-dimensional V-doped MoS₂ electrocatalysts were fabricated via a solvothermal method using sodium molybdate as Mo source,sodium vanadate as V source,thiourea as S source.Through modulating the Mo/V molar ratio during the synthesis,the structure,size and morphology and hydrogen evolution property can be controlled.When the molar ratio of Mo/V was fixed at 1:1,the hydrogen evolution performace of the obtained V-doped MoS₂ electrocatalysts can be largely improved.