Design Of Transition Metal Sulfide Composites And Study On Their Electrocatalytic Properties

With the aggravation of environmental problems and the emergence of energy crisis,searching for renewable energy resources to replace the traditional fossil fuels has become the most urgent task.In recent years,metal-air battery and electric hydrolysis system have attracted much attention as efficient and environmentally friendly electrochemical energy conversion systems.However,the electrochemical reaction kinetics of these two kinds of electrochemical energy conversion systems are slow.Moreover,the electrocatalysts required for the reactions are faced with high price and low reserves,thereby drastically limiting their large-scale application.It is thus vitally important to develop non-noble metal catalysts with excellent performance to meet the large-scale application requirements.In this thesis,a series of composite catalysts with excellent bifunctional properties were prepared based on transition metal sulfides and successfully used as cathodes for zinc-air batteries and catalytic electrodes for electrohydrolysis systems.The specific research content and results include the following three aspects:(1)First,a series of transition metal sulfide and graphene oxide composite catalysts were prepared by solvothermal method.Through the analysis of characterization results,it was found that Co_xFe_yS_z/r GO catalyst could support more active sites,graphene oxide surface was bonded with transition metal sulfides,and bimetallic synergistic effect was produced,resulting in the excellent catalytic excellent catalytic performance and stability for oxygen reduction(E_1/2=0.85 V)and oxygen evolution(E₁₀=1.66 V)(The attenuation of E_1/2and E₁₀is small).The rechargeable zinc-air battery assembled with it has excellent charge and discharge capabilities.However,it exists in the form of powder.In practical applications,it is necessary to use a binder to fix it on the working electrode,which reduces the catalytic efficiency.Therefore,it is imperative to develop a self-supporting catalyst.(2)The transition metal sulfide was in-situ grown on the surface of the copper mesh by solvothermal method.The characterization results show that Co_xZn_yS_z/Cu-F catalyst has a three-dimensional structure which can increase the active surface area and electrolyte diffusion rate.Moreover,the transition metal sulfides are firmly attached to the surface of the copper mesh,resulting in the excellent electrocatalytic activity and durability of the self-supporting Co_xZn_yS_z/Cu-F mesh electrode for oxygen evolution(E₂₀=1.44 V)and hydrogen evolution(E_-20=-0.18 V)(E₂₀and E_-20have little attenuation).It also showed very good electrolysis performance for overall water splitting.(3)MXene is an important energy storage material emerging in recent years due to its excellent physical and chemical properties.In the third part of the thesis,MXene was first compounded with copper mesh by solvothermal method,and Fe S/MXene/Cu-F mesh electrode was finally prepared through S-doping.The characterization results show that Fe S/MXene/Cu-F catalyst has unique layered structure,high conductivity and hydrophilicity.Moreover,this unique structure is conducive to improving charge transfer rate,fast approaching electrolyte and accelerating gas release,resulting in the as-synthesized Fe S/MXene/Cu-F mesh electrode exhibited excellent catalytic activity and durability of oxygen evolution(E₂₀=1.45 V)and hydrogen evolution(E_-20=-0.17 V)under alkaline conditions(E₂₀and E_-20have little attenuation).It also showed excellent performance for overall water splitting.