Mechanistic Study of Highly Active Bifunctional Double-Atom Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions

Dual-atom catalysts (DACs) can be very effective for catalyzing both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we present theoretical evidence of a new class of highly active DACs, namely, the double-atom embedded in nitrogen-doped graphene sheet 2M-N-C (M = Mn, Fe) on the basis of density functional theory calculations. Importantly, we find that the double active sites of 2M-N-C DACs entail an unconventional catalytic reaction pathway for ORR and OER. We also show that the local coordination environment of the active sites can significantly affect the stability and oxygen catalytic activity of 2M-N-C DACs. In particular, MnFe-N-C DAC not only exhibits good stability but also possesses outstanding bifunctional ORR/OER catalytic activity with the potential difference (Δ<i>E</i>) between the OER and ORR as low as 0.34 V, notably lower than most bifunctional electrocatalysts reported in the literature. This finding suggests a new strategy toward the design of stable and highly active bifunctional electrocatalysts for both ORR/OER.