Doping Of Rhenium Disulfide Nanosheets For Enhanced Hydrogen Evolution Performance

Two-dimensional(2D)layered ReS₂ nanosheets have a unique electronic structure of 1T'phase,and their electronic properties are independent of thickness.These characteristics distinguish ReS₂ from other 2D transition metal chalcogenides(TMDs)used as catalysts in the hydrogen evolution reaction(HER),and make it a suitable replacement catalyst for the most common expensive Pt towares HER.Similar to traditional TMDs,the catalytic activity of ReS₂ is mainly contributed by edge sites,while the base surface,which accounts for a large percentage of the surface area,has a poor catalytic activity.Activation of the ReS₂base surface will be an ideal strategy to improve its catalytic performance.In this thesis,through a simple synthesis method,ReS₂ nanosheets doped with transition metal atoms(Mo,V)were prepared,and the application of the impurity atom doped ReS₂ nanosheets in the electrocatalytic hydrogen evolution reaction was studied.The main findings are as follows:(1)A one-step hydrothermal method was reported to synthesize Mo-doped ReS₂ nanosheets,and the effect of Mo doping content on HER performance was studied.The as-prepared Mo-doped ReS₂ nanosheets have a ultrathin thickness of 3.25 nm,these small nanosheets are assembled to form hierarchical nanospheres with diameters of 40-50 nm.The number of exposed active sites of the electrocatalyst was greatly increased owing to the hierarchical structure and Mo-doping.The catalytic activity of ReS₂ basal plane can be effectively activated by doping with Mo.Doping with Mo can not only significantly reduce the free energy of hydrogen adsorption(?G_H^*)by adjusting the adsorption behavior of H atoms on the ReS₂ surface,but also can expose more active sites by introducing more unsaturated electrons.The 10%Mo-ReS₂catalyst has significantly enhanced HER performance with a small Tafel slope of 62m V dec^-1,a low overpotential of 81 m V at the current density of 10 m A cm^-2,and the long-term operation stability of 50 h.(2)A simple solvothermal method was developed to prepare interlayer-expanded and V-doped ReS₂ nanosheets.On the one hand,the interlayers of ReS₂ nanosheets are intercalated by Octylamine molecule from the n-octylamine solvent,resulting in interlayer expansion.Abundant defects are formed and more active sites are exposed owing to the interlayer expansion.On the other hand,the forbidden band width of the catalyst is reduced by V doping,which facilitates the fast charge transfer and accelerated reaction kinetics.In addition,V-S bondsat both the edge sites and the base planes have high catalytic activities.According to the literature,the hydrogen absorption free energy of the VS₂ base surface is calculated as?G_H^*=-0.16 e V,which is much smaller than the ReS₂ base surface(?G_H^*=+1.751e V).V doping may optimize the hydrogen Gibbs free energy of the ReS₂ base surface.Our results show that the freshly-prepared 10%V-doped ReS₂ nanosheets exhibit HER performance with a low Tafel slope of 55 m V dec^-1,a low overpotential of 83 m V at 10 m A cm^-2,long-term operation stability of 80 h.These prove that interlayer-expanded and V-doped ReS₂ can improve the catalytic HER performance.