Multi-doped Graphene As Catalysts For Oxygen Reduction And Evolution:Theoretical Consideration

Graphene-based materials have been demonstrated to be effective bifunctional catalysts for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).With the rising interest in developing graphene-based catalysts,it’s urgently needed to reveal the origin of the improved catalytic performance and establish design principle that would provide guidance and accelerate the discovery of the catalysts with desired bifunctional or multifunctional catalytic properties for clean energy technologies.In this work,Density Functional Theory(DFT)calculations were performed by VASP to reveal the synergistic effect between different type of dopants and the relationship between the catalytic performance and the intrinsic properties of active sites on graphene-based materials.The main results are summarized as follows:1.Theoretical research on the electrocatalytic performance of heteroatoms and structural defects co-doped graphene indicated that the introduction of structural defects to heteroatoms doped graphene can cause charge transfer from C atoms on graphene to the edge of defects,which led to more positive electronic distribution as well as more satisfactory catalytic performance for ORR/OER.Theoretical research on the electrocatalytic performance of heteroatoms and edge effect co-doped graphene showed that the introduction of edges to heteroatoms doped graphene can generate more localized spin density distribution,which is more favorable for ORR/OER.DFT calculations of the composite structure of Co compound and heteroatoms doped graphene indicated that the introduction of Co compound can cause charge transfer from the graphene substrate to the upper Co compound.And the doping of P can weaken the tendency of the charge transfer and change the location of pseudogap,which can make it more favorable for the adsorption of the reaction intermediates.2.In the theoretical research of the intrinsic mechanism for the catalytic performance of graphene-based materials,we proposed a universal descriptor(pz-center)based on pz-orbital property of active sites on the host graphene lattice for the ORR and OER activities of graphene-based materials.Crystal orbital Hamilton population analyses demonstrated that there is less filling of antibonding states for edge C-O orbital pairs than that for graphitic C-O orbital pairs with the same value of pz-center,which makes edge-C more favorable for the adsorption of OH*.DFT calculation showed that this new descriptor can well descript the relationship between the catalytic performance and the intrinsic properties of active sites on graphene and predict the catalytic activity of dual-doped graphene or tri-doped graphene with defects.Our results provide a comprehensive understanding for the catalytic mechanism of graphene-based materials,and the descriptor we carried out enables us to design new catalysts for ORR/OER based on graphene or other sp2 carbon materials.