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

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 O-2 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 O-2 dissociation reaction. The lowest calculated ORR over-potentials 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 over- potential of the catalyst by similar to 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.