Preparation And Electrocatalytic Hydrogen Evolution Of MoS₂/carbon Composites

With the increasing demand of energy and environmental protection on the global scale,development of technologies for clean and sustainable energy has been given great attention.As an alternative and renewable energy source,hydrogen has been hailed as a promising candidate to ameliorate the climate change and environmental problems associated with the combustion of fossil fuels.Electrocatalytic hydrogen evolution is one of the most efficient means of producing hydrogen.When compared with traditional Pt noble metal catalysts,molybdenum disulfide（MoS₂）in transition metals has become a hotspot in the field of electrolytic hydrogen catalyst because of its low cost and high performance.However,the layered stacking and metal-semiconductor properties of MoS₂ materials are not conducive to the application in the electrocatalytic direction.Based on the characteristics and existing defects of MoS₂,this paper mainly designs a new type of MoS₂-based catalyst,which is effective in increasing the exposured active sites and improving the conductive properties of MoS₂,to achieve the high performance of electrocatalytic hydrogen evolution.The research contents of thesis are as follows:1.A three-dimensional MoS₂/nitrogen-doped graphene（MoS₂/N-rGO）hydrogel was prepared by simple one-step hydrothermal method using ammonium thiomolybdate as precursor,and the catalyst was applied to electrocatalytic hydrogen evolution.The effects of nitrogen doping on the morphology and catalytic properties of the composites were investigated by adjusting the volume of ammonia.The results showed that the appropriate amount of ammonia could effectively regulate the growth state and size of MoS₂ on N-rGO,obtaining vertical MoS₂ sheets and effectively increasing the electrocatalytic activity center of hydrogen evolution..The depleted negative charge on the nitrogen atom of N-rGO can be transferred to the planar carbon atoms to maintain the higher conductivity of the composite.The self-assembled threedimensional N-rGO framework not only provides a good attachment site for the growth of MoS₂,but also provides a convenient transmission channel for the transfer of the electrolyte.MoS₂/N-rGO0.5 hydrogels exhibit superior electrocatalytic hydrogen evolution performance,including smaller onset overpotential of 119 mV,smaller Tafel slope of 36mV/decade and good stability.2.The MoS₂/molybdenum disulfide/carbon（MoS₂/MoO₂/C）composites were prepared by the traditional solvent method,by using molybdenum trioxide as molybdenum source,thiourea as sulfur source and carbon cloth as growth substrate,and studied as catalysts in electrocatalytic hydrogen evolution.Experimental results show that the effective regulation of the sulfidization time in the reaction system is the key to obtain MoS₂/MoO₂/C composites.The ultra-thin MoS₂ nanosheets with exposed edges adhere to the edge of the MoO₂ sheet and provide more active centers for the catalytic reaction.Simultaneously,MoS₂ as a protective shell for MoO₂ can effectively prevent MoO₂ from being corroded by the acidic electrolyte.MoO₂ with good conductivity not only increases the hydrogen evolution site,but also provides a convenient channel for the transmission of electrons between MoS₂ and carbon cloth.A good synergistic effect between MoS₂ and MoO₂ promote the electrocatalytic hydrogen evolution reaction.On the other hand,as a load substrate,carbon cloth with a huge surface area and three-dimensional structure provides a restricted environment for the growth of MoS₂/MoO₂,and reduces the transmission distance of the electrolyte.In addition,the carbon cloth has good electrical conductivity and independence,and can be used as a self-supported electrode,avoiding the addition of other adhesives.Based on the above advantages of MoS₂/MoO₂/C composites,they exhibit excellent HER performance,including a smaller onset overpotential of 85 mV and a smaller Tafel slope of 38 mV/decade.