Preparation And Electrocatalytic Hydrogen Evolution Properties Of Double Transition Metal MXene Based Composites

Hydrogen energy is one of the candidates for renewable energy and green energy because of its high energy density and zero pollution emission.Two dimensional MXene materials have many advantages,such as large specific surface area,layered structure,rich active sites and so on.In this thesis,MXene and transition metal sulfides were studied.Nanomaterials were prepared by hydrothermal method and in-situ vulcanization.The chemical composition,morphology,growth mechanism and application in electrocatalytic hydrogen evolution of these nanomaterials were explored.The main contents of this thesis are as follows:（1）Multilayer Ti₂VC₂T_x MXene was successfully synthesized by etching Ti₂VAl C₂ with hydrofluoric acid（HF）.Ti₂VC₂T_x/Mo S₂ nano heterostructures were prepared by hydrothermal synthesis,and hydroxylated carbon nanotubes（CNTs）were added to improve their conductivity.The hydrogen evolution performance of the catalyst was prepared with the conditions of different mass ratio,different catalyst loading and different CNTs addition.The results show that the hydrogen evolution performance reaches the best when the mass ratio of Ti₂VC₂T_x/Mo S₂ to CNTs is 5:1,the mass ratio of Ti₂VC₂T_x is 20 mg,the mass ratio of ammonium molybdate tetrahydrate（AMT）is 78 mg.The overpotential and Tafel slope are 183 m V（10mA/cm~2）and 83 mv/dec,respectively.Ti₂VC₂T_x MXene is used as the growth skeleton of Mo S₂,which is conducive to the dispersion of Mo S₂ nano sheets,improve the conductivity of Mo S₂ and expose more active sites.In addition,the stability test shows that the heterostructure can maintain catalytic activity for a long time.（2）Multilayer Ti VCT_x was successfully synthesized by etching Ti VAl C with HCl/Li F.Ti VCT_x/Mo S₂ nanoheterostructure was prepared by hydrothermal synthesis,and hydroxylated CNTs were added to improve their conductivity.The hydrogen evolution performance of the catalyst with the conditions of different mass ratio,different catalyst loading and different CNTs addition was investigated.The results show that the overpotential and Tafel slope are 180 m V（10 mA/cm~2）and 79 m V/dec,respectively.The nanoheterostructures of catalyst not only enhances the conductivity of Mo S₂,but also activates its inert surface activity.The stability test shows that the heterostructure can maintain catalytic activity for a long time.（3）Mo₂Ti C₂T_x was successfully synthesized by etching Mo₂Ti Al C₂ with HF.In addition,Ni-MOF material was prepared by solution blending method.Mo₂Ti C₂T_x/MOF was first obtained by hydrothermal method and Mo₂Ti C₂T_x/Mo NiS was obtained by sulfide The hydrogen evolution properties with different Mo₂Ti C₂T_xand MOF mass ratios and different hydrothermal temperatures were investigated.The results show that the hydrogen evolution performance reaches the best when the mass ratio of Mo₂Ti C₂T_x and MOF is 1:4.The overpotential and Tafel slope are 153 m V and 92 m V/dec,respectively.MOF-derived Ni₂S can tune the electronic properties of Mo₂Ti C₂T_x/Mo NiS heterostructures and reduce the aggregation of Mo₂Ti C₂T_x.The oxide layer on the surface of MXene is converted into Mo S₂ after in-situ sulfide,thereby enhancing the HER performance.A hybrid system with excellent electron and ion transport properties is formed between Mo₂Ti C₂T_x/Mo S₂ and Ni₂S.Furthermore,the stability indicates that the heterostructure can maintain catalytic activity for a long time.