Computational Insight into TM-N x Embedded Graphene Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions.

Due to the energy crisis, development of bifunctional electrocatalysts for both oxygen evolution and reduction reactions is highly demanding. In this study, we have systematically investigated the bifunctional activity of metal (Co/Rh/Ir) and N co-doped graphene systems with varying N-dopant concentrations (TM-N x @G, x = 0, 2, 4) using first-principles calculations. Charge transfer from the metal sites to the adsorbed intermediates and the adsorption free energy of the intermediates play important roles to help understand the potential-determining step and overpotential values for oxygen evolution reaction (OER)/oxygen reduction reaction (ORR). A dual volcano plot for all the systems using a common descriptor Δ G OH* has been constructed. We find that the systems having Δ G OH* values in the range of 0.40-0.70 eV can act as bifunctional electrocatalysts. Our study not only highlights the importance of metal and non-metal co-doped graphene as bifunctional catalysts but also can serve as a promising strategy for the design of efficient OER/ORR electrocatalysts.