Engineering Isolated Mn-N2C2 Atomic Interface Sites for Efficient Bifunctional Oxygen Reduction and Evolution Reaction.

Oxygen involved electrochemical reactions are crucial for plenty of energy conversion techniques. Herein, we rationally designed a carbon based Mn-N2C2 bifunctional electrocatalyst. It exhibites half-wave potential of 0.915 V vs. RHE for oxygen reduction reaction (ORR) and the overpotential is 350 mV at 10 mA cm-2 during oxygen evolution reaction (OER) in alkaline condition. Furthermore, by means of operando X-ray absorption fine structure measurements, we revealed that the bond-length-extended Mn2+-N2C2 atomic interface sites acted as active centers during ORR process, while the bond-length-shortened high-valence Mn4+-N2C2 moieties served as the catalytic sites for OER, which is consistent with the density functional theory resluts. The atomic and electronic synergistic effects for the isolated Mn sites and the carbon support played a critical role to promote the oxygen-involved catalytic performance, by regulating the reaction free energy of intermediate adsorption. Our results gave an atomic interface strategy for non-precious bifunctional single atom electrocatalysts.