Role of active sites in N-coordinated Fe-Co dual-metal doped graphene for oxygen reduction and evolution reactions: A theoretical insight

Identifying the atomic-scale structures of active sites is crucial to develop Fe-Co dual-metal doped N-coordinated graphene (Fe-Co-N-C) as a promising electrode material for fuel cell or metal-air batteries but remains debatable. Here the catalytic performance of Fe-Co-N-C with different active sites, including FeCoN6, FeCoN7, and FeCoN8, towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is systematically studied by density functional theory calculations. We show that the stability and catalytic activity of Fe-Co-N-C for ORR and OER would be affected by the atomic-structures of active sites, and Fe-Co-N-C with active sites of FeCoN7 and FeCoN8 possess a better catalytic performance compared with FeCoN6. The top site of Co atom is the main active center responsible for ORR and OER in active sites of FeCoN7 and FeCoN8, in which the extremely low overpotential of 0.22 V for both ORR and OER can be obtained by regulating the atomic-structure of the active site. Importantly, we plot the relationship curve between the d-band center of Co atoms and overpotentials of ORR and OER on Fe-Co-N-C, which can link the atomic-structure of active sites to catalytic performance. These findings are great significance for the scientific design of efficient bifunctional catalysts.