First Principles Study of Morphology, Doping Level and Water Solvation Effects on Catalytic Mechanism of a Graphene Towards Oxygen Reduction Reaction

Abstract

First principles density functional theory calculations are utilized to unveil oxygen reduction reaction mechanisms on nitrogen doped graphene (N-Gr). Considering the effect of both the geometry and concentration of N in bulk and edge N-Gr forms, we calculate the energies of a large number of model systems to cover a wide range of possible N-Gr structures and determine the most stable ones. In agreement with experiments, our calculations suggest that doping levels in stable N-Gr forms are limited to less than about 30 at.%, above which the hexagonal graphene framework is broken. Remarkably, the ground state structures of bulk and edge N-Gr are found to differ depending on the doping level and poisoning of the edge bonds. ORR mechanisms are estimated using Gibbs free energy diagrams, both with and without water solvation. Our results indicate that N doping significantly alters the catalytic properties of pure graphene and that dilutely doped bulk N-Gr forms are the most active. ⓒ 2015 DGIST