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.