Influence of the Atomic Local Environment on the ORR Activity of Single-Atom Catalysts in N-Doped Graphene

Using density functional theory, we have studied a graphene structure with a single C vacancy, doped with three pyridinic N atoms and a single metallic adatom (Fe, Ni, and Cu) as a catalyst for the oxygen reduction reaction (ORR), one of the most critical reactions in electrocatalysis. Nitrogen(N)-doped graphitic structures are promising candidates for the ORR, and the incorporation of metallic adatoms could improve their activity. Previous experimental and theoretical reports indicate that Fe favors the four-electron pathway, resulting in the formation of water molecules. On the other hand, Ni and Cu favor the two-electron pathway, producing hydrogen peroxide molecules. Our calculations show that in the case of a single C vacancy with three pyridinic N atoms, the reaction proceeded via the four-electron pathway for either Fe, Ni, or Cu. This result differs from the case of two C vacancies and four N atoms. Therefore, the chemical environment of single-atom catalysis plays an essential role in the reaction.