Theoretical Study On The Structure,composition And Hydrogen Evolution Of Co_xS_y Clusters

As an important part of nano-science,the cluster science has been rapidly developed in the aspects of both fundamental research and applications in the past decade.The synthesis of hierarchical solids is a hot and promising research topic in cluster science.In this aspect,Co8S6(PH3)8 cluster is one of the most potential candidates for constructing layered materials.However,the theoretical studies of Co8S6 and its various ligands are not sufficient.Here,we performed systematic density functional theory(DFT)calculations on structure stability,electrical and magnetic properties of the ground state Co8S6(PH3)8 cluster,as well as the effects of ligand replacements and transition metal atoms embedding on the properties above.The electromagnetic stability and HER performance of Co8S6 and Co6S8 clusters were then discussed,providing some predictions in the improvement of HER activity in CoS binary clusters.It was found that the ground state structure of the Co8S6(PH3)8 cluster is an antiferromagnetic(AFM)configuration,and spin-up and spin-down magnetic moments are alternately arranged along the y-direction.The replacement of CO ligands didn't change the AFM feature of Co8S6(PH3)8-x(CO)x clusters,and their ground state structures support symmetrical substitution of ligands.The CO ligands act as the charge acceptor,which causes the partial charge transfer from neighboring Co atoms to CO and thus the magnetic moment distributions of Co8S6(PH3)8-x(CO)x clusters are ununiform.The increasing number of CO ligands enhances the activity of the cluster,which is manifested in the gradual increase in affinity and ionization energy.This theory is vital for the applications of semiconductor dopants and superatoms assembled from clusters.Secondly,we studied the effect of transition metal(TM)atom embedding on the structure and electronic features of Co8S6(PH3)8 cluster.It was found that the presence of TM atoms slightly expanded its structure,and made the interaction between the Co-S "cage" and the PH3 ligand stronger,which further stabilized the cluster.The newly formed TM@Co8S6(PH3)8 still maintains antiferromagnetic properties,but the AFM configuration has a "spin boundary" on the(111)plane of the Co cube.The charge transfer and interaction between TM and Co atoms lead to the generation of a larger HOMO-LUMO gap,which significantly enhances the stability of the cluster and also completely quenches the magnetic moment of TM atoms.The current theoretical research results provide theoretical support for people to control the magnetic properties of clusters by intercalating transition metal atoms.Finally,we compared the ground states of Co8S6 and Co6S8 clusters,and found that Co8S6 is AFM configuration and Co6S8 is FM configuration.HER calculations show that the hydrogen evolution performance of Co6S8 is better than Co8S6,and the S site of Co6S8 is the ideal hydrogen evolution site.This theoretical discovery is helpful to stimulate people's interest in selecting new CoS clusters as nano catalysts,thereby expanding the applications of CoS clusters in the field of electrocatalysis.