Construction And Performance Of Transition Metal Sulfur、Selenide Heterostructures Electrocatalysts For Alkaline Hydrogen Evolution Reaction

Hydrogen is a green,high calorific value secondary energy source that can be used to replace increasingly depleted fossil energy sources.Electrolyzers powered by renewable energy can not only fully absorb renewable energy such as wind and solar that are currently available to humans,but also convert them into hydrogen energy and use them in industries and transportation.As a more mature means of hydrogen production,alkaline electrolytic water technology can meet the requirements of industrial hydrogen production.However,hydrogen evolution reaction（HER）in alkaline environment requires a water dissociation step with high activation barrier,which raises the electrolysis reaction potential.The use of catalysts can reduce the electrolysis reaction potential and increase the kinetic rate of HER.The best performing catalysts in alkaline environments are noble metal-based catalysts（Pt,Ru and Ir,etc.）,but the expensive price and scarce crustal abundance limit their use.Transition metal sulfides and selenides contain great potential for application because of their high crustal content,unique physicochemical properties and good electrochemical HER activity.The alkaline HER involve H,H₂O and OH adsorption intermediates,and their reaction processes are relatively complex.It is shown that the construction of heterogeneous structures is important for reactions involving multiple intermediates.By constructing heterogeneous structures,the synergistic effect of different components can be exploited to improve the catalytic activity of HER,and the kinetic rate of alkaline HER can be improved by reducing the water dissociation energy barrier of the catalyst through the introduction of water dissociation sites and other strategies.In this paper,we constructed heterostructures with molybdenum diselenide and trinickel disulfide and successfully enhanced their catalytic performance for alkaline HER.First,to obtain 1T-phase molybdenum diselenide（1T-Mo Se₂）with higher HER activity and enhance its application in alkaline hydrogen evolution reaction,we combined phase engineering and heterostructure engineering and used a two-step hydrothermal method to load heterostructured Mo Se₂/Ni_0.85Se/Cu₂Se containing 1T-Mo Se₂ nanosheets on carbon cloth.It was shown that the HER activity and electronic conductivity of the catalysts were effectively enhanced thanks to the 1T-Mo Se₂component in the heterostructure.It is shown that the Cu₂Se component of the heterostructure plays an electron-modulating role,and its HER activity is enhanced by electron injection into 1T-Mo Se₂ through electron tuning at the interface.In addition,the slow kinetic process of water molecule cleavage was promoted by the good water dissociation ability of Ni_0.85Se under alkaline environment.Finally,the above heterostructure is loaded on the carbon cloth,which has a high density of active sites and avoids the disadvantages such as obscuring the active sites caused by the use of binder.As a result,the heterostructure exhibits excellent hydrogen precipitation performance when used as a basic hydrogen precipitation catalyst:a low overpotential of 52 m V（vs RHE）is required to achieve a current density of 10 m A cm^-2,the Tafel slope is only 51 m V dec^-1,and it has good electrochemical stability.Secondly,we constructed the heterostructure Cu₂S@Ni₃S₂.Using hydrothermal technique,we successfully loaded the above heterostructure on the porous nickel foam3D skeleton,which consists of Cu₂S nanosheets loaded on Ni₃S₂ polyhedra.Described as Cu₂S@Ni₃S₂/NF,it is a three-dimensional hierarchical structure,which facilitates the exposure of active sites and bubble mass transfer process.A hydrogen spill-over strategy was successfully introduced in the heterostructure Cu₂S@Ni₃S₂ to avoid the limitation of Sabatier’s principle and achieve the separation of hydrogen capture and hydrogen precipitation sites.The hydrogen spill-over process in Cu₂S@Ni₃S₂ was confirmed by density functional theory（DFT）calculations and electrochemical experiments.In addition,the electron transfer at the heterogeneous interface further enhances the water dissociation of Ni₃S₂.Thanks to the advantage of its morphological structure,the self-supported electrode Cu₂S@Ni₃S₂/NF has a high density of active sites.When used as a basic HER catalyst,an overpotential of only 39 m V is required to achieve a current density of 10 m A cm^-2.When used as an alkaline HER catalyst,an overpotential of only 39 m V is required to achieve a current density of 10 m A cm^-2.It also exhibits excellent electrochemical stability with stable operation at current densities of 20 and 100 m A cm^-2 for 24 hours.