Theoretical Study Of Pentlandite On Structure And Electrocatalytic Hydrogen Evolution

Nowadays,fossil fuels are the main energy suppliers.With the rise of environment awareness and the depletion of traditional energy resources,hydrogen energy has attracted more attention as a renewable and environment-friendly energy.The electrocatalytic hydrogen evolution is one of the important methods to obtain hydrogen.It is necessary to seek an efficient and low-cost catalyst to trigger the industrial popularization on a large scale.Pentlandite is one high metal content transition metal sulfide composed of Fe,Ni and S atoms with a ratio of 9:8 between metal and sulfur atoms.Due to its abundance,low-cost,high metal content,good conductivity and stability,pentlandite has been studied toward hydrogen evolution reaction in recent years.In previous studies,(111)and(311)facets have been introduced as catalytic surfaces,and sulfur vacancy have been suggested as one possible catalytic active site.However,due to the argument about the explicit metal distribution,atomic scale mechanism of catalytic active site with electronic structure is still in infancy.The lack of theoretical research impedes the understanding of pentlandite on catalytic activity and subsequent modification research.Therefore,it is important to establish an explicit metal distribution model and electronic structures of pentlandite.In this study,we paid attention to the structure model with rational distribution of Fe/Ni and catalytic active sites on each surface,and the contents are as follows:(1)At firstly we discuss the influence of metal distribution on structure stability indicating that the model with heterogeneous distribution in tetrahedral metal sites,which form a cube moiety by 8 Fe/Ni atoms,shows better stability,and it even has the lowest formation energy than reported one.Consequently,a rational model structure is provided for subsequent theory study.(2)Based on the proposed model,the hydrogen adsorption of(100),(111)and(311)facets have been studied.On(100)facet,Fe and Ni atoms co-regulate the electronic structures of connected bridge site S with synergistic effect and make it to be active site.(311)is composed by stacking(111)facets with a step shape and the basal plane of(311)is the same as(111)facet.The step edge site of(311)is similar to bimetallic bridge sulfur active site on(100)plane and possess approximate performance.The active sites of basal plane are the connection Fe and S atoms of adjacent cubes,and the cross section of up and bottom step also presents comparable performance with bimetal co-catalytic sites.(311)facet integrates the active site of(111)with(311),and has additional active sites from basal planes overlapping without additional modification.We introduced one probable structure model on Fe/Ni distribution,which provides one solution for model controversy.Based on proposed structure model,cube moiety plays an important role in structure and surface configuration and is the reason for long activation process.In the part of the relation of different facets and catalytic active sites,the synergistic effect from adjacent Fe and Ni atoms and the interactions between cube atoms fill the vacancy about mechanism of pentlandite in theory,which is benefit for subsequent modification research.