Dissociative Oxygen Reduction Reaction Mechanism on the Neighboring Active Sites of a Boron-Doped Pyrolyzed Fe–N–C Catalyst

Abstract

We study the oxygen reduction reaction (ORR) mechanism on the neighboring active sites of a B-doped pyrolyzed Fe–N–C catalyst using a combination of density functional theory-based calculations and microkinetic simulations. The structure of the neighboring FeN4 and B-doped active sites facilitates the O2 side-on adsorption for a facile dissociation process. This situation gives the B-doped catalyst system a flexibility to access both associative and dissociative reduction mechanisms. Such a mechanism does not exist in the undoped catalyst system because its dissociative mechanism is greatly hindered by the high activation energy for the O2 dissociation reaction. The lowest calculated ORR overpotentials for the B-doped catalyst system through the associative and dissociative reduction mechanisms are 0.74 and 0.65 V, respectively. The ease of access to the dissociative reduction mechanism improves the ORR overpotential of the catalyst by ∼0.1 V with respect to the associative reduction mechanism. These results demonstrate the origin of superior performance of the B-doped pyrolyzed Fe–N–C catalyst system, which has been observed from experiments.