On the Mechanism of the Oxygen Reduction Reaction on Nitrogen-Doped Graphenes in Alkaline Media

Nitrogen-doped graphene-like materials exhibit high catalytic activity and stability in the oxygen reduction reaction. Theoretical studies of catalytic activity based on DFT calculations typically assume that the reaction proceeds via an inner-sphere mechanism involving the chemisorption of an oxygen molecule. In this work, using grand-canonical DFT calculations we demonstrate that, in an alkaline medium, an outer-sphere reaction mechanism, initiated with an electron transfer to a solvated O2 molecule near the surface, is energetically more favorable. On N-doped graphene containing graphitic nitrogen atoms, the reaction proceeds via a 4e mechanism due to a significant reduction in the chemisorption energy of the *OH intermediate, whereas on pristine graphene, the reaction terminates after two electron transfers.