The Electronic Structure Of Ultra-thin Noble Metal/graphene Heterostrctures:A First-principles Study

We studied the structural,electronic and magnetic properties of the ultra-thin noble metal(Pd,Rh)and the compound system(single-layer Rh/graphene)by using the first-principles methods based on density functional theory.We illuminated the ground-state properties of the ultra-thin noble metal and the related physical mechanism of the single-layer Rh/graphene from the views of low dimensional material science,quantum size effect and computational physics.In addition,we reported the characteristics and applications in electrochemical catalysis of the ultra-thin noble metal sheets and single-layer Rh/graphene.First,we studied the classical noble metals Rh and Pd in order to elucidate the distinctions among bulk,single-layer,multilayer phases.Taking into consideration that the crystal face(111)is the close-packed face of these two FCC metals,we obtained the slab models by cleaving(111)crystal face from bulk Rh and bulk Pd.The calculated results of structural and electronic properties showed that the monolayer Rh emerges a magnetic moment 1.2?B/Rh which derived from the contribution of the dz orbital whereas bilayer Rh and bulk Rh had no magnetic moment.This phenomenon might imply that monolayer Rh can provide more active sites than bulk Rh for electrochemical catalytic reaction,which makes reaction rate efficiently.Compared with Rh,bulk Pd and Pd sheets both presented a weak magnetic moment with a value?0.4?B per Pd atom.The magnetic property of Pd will not be unusual with the configuration change.Next,in view of the magnetic moment of a free-standing monolayer Rh,we introduced graphene to combine with single-layer Rh to construct a single-layer Rh/graphene(Rh/G)heterostructure for studying its change in physical property.The structural changes showed that both single-layer Rh and graphene are wrinkled.And the corrugation in graphene is more remarkable than that in single-layer Rh.Interestingly,the single-layer Rh presented the same corrugation rule and corrugation region as graphene.Moreover,we found that the equally distributed magnetic moment in the monolayer Rh was localized and become isolated magnetic domains.In some areas,magnetic moment disappears due to the hybridization between C-2p and Rh-4d orbitals.Finally,we studied the hydrogen evolution reaction on the ultra-thin Rh/G.The Gibbs free energy revealed that the performance in Rh/G for hydrogen adsorption is better than Pt and Rh laminate.In the full attraction region(FAR)?G(Rh/G)is-0.07eV,which is closer to the summit of volcano than Pt and Rh metal.