Preparation Of MoS₂-based Catalytic Materials And Their Applications In Hydrogen Evolution Reaction

The energy and environmental issues derived from the extensive usage of traditional fossil fuels make the development of new types of clean energy an inevitable part of social development.Hydrogen is an ideal clean energy with a high energy density,a pollution-free production of only water and abundant reserves.Besides,the production and utilization process of green hydrogen will not generate carbon emissions,which is of great significance for the low-carbon transformation of energy.At present,the large-scale production of green hydrogen is limited by the high cost of water electrolysis.During the water electrolysis process in the proton exchange membrane electrolyzer,Pt-based materials are commercially used in hydrogen evolution reaction（HER）at the cathode,which is a key factor in the high cost.Developing alternative non-precious metal-based catalysts is an effective approach to reduce the cost of HER process.The two-dimensional material MoS₂ has the advantages of abundant reserves,low cost and moderate hydrogen absorption free energy,making it a promising alternative HER catalyst to Pt-based materials.Nonetheless,as HER catalysts,MoS₂-based materials suffer from limited active sites,intrinsic activity and conductivity,which needs to be improved urgently.In response to the above issues,the following research works have been carried out aiming to modify MoS₂-based HER catalysts.（1）Preparation of eggshell-like MoS₂ and its application in HERRegarding the issues of limited active sites and insufficient intrinsic activity in MoS₂-based HER catalysts,a pure phase eggshell-like MoS₂ was designed and prepared through a template removal method in this part,which simultaneously brings massive active sites and boosts the intrinsic activity.As a HER catalyst,the eggshell-like MoS₂ shows excellent activity,with an overpotential of 180 m V at–10 m A cm^–2.Such a performance ascribes to:（i）the design of eggshell structure not only makes more edge sites exposed in MoS₂,but also converts the inert plane of MoS₂ into active surface with negative curvature,creating massive active sites;and（ii）the negative curvature surface and stepped face formed along with the eggshell-like structure can reduce the hydrogen adsorption of MoS₂,making it present enhanced intrinsic HER activity.（2）Preparation of rGO/Cu-MoS₂ and its application in HERThe conductivity of pure phase MoS₂ is insufficient,which is still to be solved.Therefore,a material of rGO with high conductivity was proposed to serve as the substrate of MoS₂ in this part,which will bring more exposed active sites and improved conductivity in MoS₂.In addition,further introduction of Cu element in the composite can modify the electronic structure of MoS₂,thus enhancing the intrinsic HER activity.The composite rGO/Cu-MoS₂ prepared through the above dual modification method presents excellent HER activity,with an overpotential of 168m V at–10 m A cm^–2 and a Tafel slope of only 41.5 m V dec^–1.The advanced HER activity ascribes to the synergistic effect of multi-components:（i）as a substrate,rGO effectively disperses MoS₂ and provides good conductivity for the composite;（ii）the doping of Cu element leads to the expansion of MoS₂（002）lattice,thus optimizing its electronic structure to enhance the intrinsic activity;and（iii）the active material MoS₂presents a dense petal-like structure under the joint effect of rGO substrate and Cu doping,maximizing the exposure of edge active sites.（3）Preparation of rGO-MoS₂/TiO_2/C and its application in HERThe aforementioned works have effectively boosted the HER activity of MoS₂-based materials.However,further improvement in electrochemical stability is still demanded.For this purpose,an ultrastable TiO₂/C substrate was proposed to support MoS₂ in this part.Besides,rGO was also introduced for the better conductivity of the composite.The as-prepared rGO-MoS₂/TiO₂/C presents good HER activity,with an overpotential of 207 m V at–10 m A cm^–2.Meanwhile,the composite also shows excellent electrochemical stability,exhibiting a negligible attenuation of catalytic activity after 150,000 cycles of CV test and a 95%potential retention after a 200,000s galvanostatic measurement.The advanced HER activity of rGO-MoS₂/TiO₂/C ascribes to the synergistic effect of the three components:（i）the TiO₂/C substrate can maintain long-term stability under strong acid conditions and also provide a large number of attachment sites for active material;（ii）the active material MoS₂ vertically grows on the TiO₂/C substrate,which is beneficial for exposing more active edges and forming firm chemical bonds with the substrate to ensure the stability of the catalytic system;and（iii）the modification of rGO provides good conductivity to the composite.