Second‐Shell Coordination Environment Modulation for MnN₄ Active Sites by Oxygen Doping to Boost Oxygen Reduction Performance

Abstract

As a category of transition metal−nitrogen−carbon (M−N−C) catalysts, Mn‐based single‐atom catalysts (SACs) are considered as promising non‐precious metal catalysts for stable oxygen reduction reaction (ORR) due to their Fenton‐inactive character (versus Fe) and more abundant earth reserves (versus Ni, Co). However, their ORR activity is unsatisfactory. Besides, the structure‐activity relationship via tuning the coordination environment of the second coordination shell for transition metal single sites is still elusive. Here, a Mn SAC with O doping in the second‐shell of atomically dispersed Mn centers (MnSAC‐O/C) as highly efficient and stable ORR catalyst is developed. X‐ray absorption spectroscopy combined with theoretical calculations verifies the O doping in the second‐shell of Mn center, and reveals the distortion of local environment of Mn center in the MnSAC‐O/C. The MnSAC‐O/C exhibits high ORR performance with a half‐wave potential of 0.898 V, superior to MnSAC‐C, commercial Pt/C and most reported non‐noble metal‐based SACs. More importantly, MnSAC‐O/C based zinc‐air batteries (ZABs) deliver outstanding durability with stable operation exceeding 930 h. Theoretical calculations confirm that O doping breaks the symmetry of charge distribution of MnN4 active center and facilitates OH* desorption, thus attributing to the promoted ORR activity.