Enhancing the bifunctional oxygen reduction/evolution reaction activity of atomically dispersed zirconium on graphene using boron and nitrogen co-dopants

Abstract

We study the impact of surface engineering using boron and nitrogen co-dopant on the activity of atomically dispersed zirconium on graphene for oxygen reduction and evolution reactions (ORR/OER). We discover that the presence of boron and nitrogen co-dopants enhances the activity of the reactions. The O-Zr-N4-B active site displays excellent bifunctionality for the reactions with ORR overpotential (ηORR) of 0.33 V and OER overpotential (ηOER) of 0.23 V. However, the formation of another active site, O-Zr-N4-BN, may dominate in certain synthesis conditions, but it exhibits poorer ORR/OER bifunctionality. To understand the origin of the bifunctionality, we identify the Gibbs free energy (ΔG) that strongly correlates with the overpotential of the reactions. We discover that the regulation of -OH binding energy is the origin of ORR/OER bifunctionality. Boron doping weakens the interaction between Zr and the -OH adsorbate, which can be attributed to reduced charge density. Further addition of nitrogen doping strengthens the interaction between Zr and the oxygen-containing intermediate. These findings have the potential to aid in the development of improved catalyst materials for effective bifunctional oxygen reduction and evolution reactions.