Enhancing oxygen reduction reaction activity of pyrolyzed Fe–N–C catalyst by the inclusion of BN dopant at the graphitic edges

Abstract

We study the detailed mechanism of oxygen reduction reaction (ORR) at the graphitic edges of BN-doped pyrolyzed Fe–N–C catalyst (FeN4-BN-edge) by utilizing the combination of DFT and microkinetic calculations. We find that the ORR mechanism on FeN4-BN-edge active sites is more selective toward the associative reduction pathway for all relevant potential ranges instead of the dissociative reduction pathway. This situation arises because the O2 dissociation energies on the FeN4-BN-edge active sites are too high for the dissociative reduction pathway to take place with sufficient ORR rates. The inclusion of BN-dopant at the graphitic edge of pyrolyzed Fe–N–C is found to improve the ORR activity of the catalyst. One factor contributed to this improvement originates from the easy formation of active site configurations at the graphitic edges, which is induced by the interaction between neighboring FeN4 and BN configurations. Another factor is the formation of the FeN4-BN configuration at the zigzag edge of graphene. These active sites could improve the onset potential for the associative reduction pathway up to 0.12 V larger than that at the standard FeN4 active site in the basal plane of graphene.