Structural Regulation And Electrocatalytic Hydrogen Evolution Of Transition Metal Selenides

Hydrogen energy is one of the most important clean and renewable energy sources for future energy sustainability,and will become an important way to achieve clean energy transition in the context of the global advocacy of"dual carbon".Sustainable hydrogen production technology using renewable energy to drive electrocatalytic water cracking is considered to be the most promising commercial strategy for large-scale hydrogen production.Two-dimensional transition metal dichalcogenides（TMDs）with special graphene-like structures have attracted wide attention.Because Se has larger atomic radius,stronger gold property and lower ionization energy than S,selenide in TMDs family is more likely to be a replacement of precious metal Pt-based catalysts for electrocatalytic hydrogen evolution reaction（HER）.However,like many catalysts in the TMDs family,the high activation energy of selenide on Se on the exposed surface is unfavorable to the adsorption of H⁺.The active site of HER of the 2H phase selenide is mainly from the edge site,while the base site is inert and poor electrical conductivity hinders the practical application.In this paper,we took WSe₂and MoSe₂as the main research objects.The electrocatalytic HER performance of WSe₂and MoSe₂were further optimized through heteroatomic doping,heterostructure construction and morphology regulation.The details are as follows:（1）NiCo-WSe₂were synthesized by hydrothermal method.The overpotential of WSe₂electrocatalytic HER after metal-decreased WSe₂compared to pristine WSe₂.Specifically,Co-WSe₂has a smaller overpotential and charge transfer resistance,and Ni-WSe₂has a larger electrochemical active surface area and a smaller Tafel slope.NiCo-WSe₂obtained after co-doping with Niand Co showed an overpotential of 205 m V at 10 m A cm^-2and a Tafel slope of 118.6 m V dec^-1.Crystal structure analysis showed that Co Se₂aggregated in Co-WSe₂after Niand Co co-doping with WSe₂,but it was evenly distributed on the surface of NiCo-WSe₂.Competitive substitution between Niand Co slowed down the growth rate of Co Se₂,resulting in the formation of the Co Se₂/NiWSe₂heterostructure.The catalyst is endowed with efficient interfacial active sites,excellent electrical conductivity and enhanced electron transfer kinetics.In addition,due to the high electronegativity of Niand Co,the electron density around W and Se decreased,which changed the electron structure of WSe₂and accelerated the mass transfer efficiency between charges,thus improving the HER performance of NiCo-WSe₂.（2）The NiMo-WSe₂catalyst has been synthesized by hydrothermal reaction,with lower overpotentials of 177 and 188 m V at a current density of 10 m A cm^-2in 0.5 M H₂SO₄and 1 M KOH,respectively.The large specific surface area and thinner edge morphology provide more active sites for hydrogen production,thereby significantly improving the charge transfer kinetics.Density functional theory calculation results show that under acidic conditions theΔG_H*values of NiMo-WSe₂with different structures and hydrogen adsorption sites are also different,when the hydrogen adsorption site was located at the top of the Se-Nibond,the meta NiMo-WSe₂has aΔG_H*value（-0.04 e V）that is closest to 0.Meanwhile,NiMo-WSe₂（Meta）also has a minimum ofΔG_H*under alkaline conditions.DOS confirmed that Nidoping has a large impact on the electronic states at the WSe₂Fermi level,while NiMo co-doping greatly reduces the potential energy barrier of the HER reaction,thus improving the HER performance.（3）Ni,Mo bimetallic selenides with hollow core-shell heterostructure MoSe₂@NiSe₂were synthesized by selenization reaction combining MoSe₂with NiMOF derived NiSe₂.The spherical clusters of MoSe₂prevent the agglomeration and sintering of NiSe₂and shorten the electron transfer distance from MoSe₂to NiSe₂.The NiMOF-derived NiSe₂facilitates the catalytic process of HER by providing more active centers and better conductivity to accelerate the rate of electron transfer.In addition,the electron flow between the transition metals Niand Mo alters the electronic structure of NiSe₂and MoSe₂.Electrochemical analysis confirmed that HER activity of MoSe₂@NiSe₂increased significantly in 0.5 M H₂SO₄,with an overpotential of 187 m V at 10 m A cm^-2and a Tafel slope of 71.43 m V dec^-1.This provides a new way for the design and preparation of NiMOF based catalysts in HER.