Abstract: Developing efficient transition metal-nitrogen-carbon (TM-N-C) catalysts with abundant accessible active sites has been in the limelight in recent years due to their exceptional application potential in Zn-air batteries (ZABs). Herein, we report the simple and environmentally-friendly fabrication of a single-atom Co electrocatalyst, Co-SA/N-C₉₀₀, via in-suit pyrolysis of the co-precursor containing sucrose, dicyandiamide, and Co salts. The Co single atoms coordinated with adjacent N atoms are anchored on the doped ordered mesoporous carbon, generating the atomic Co-N₄ moiety. Co-SA/N-C₉₀₀ displays high oxygen reduction reaction (ORR) activity with an onset potential of 0.96 V and a half-wave potential of 0.87 V. Notably, the liquid ZAB with Co-SA/N-C₉₀₀ catalyst exhibits exceptional discharge specific capacity of 706.38 mAh g^-1, peak power density of 191.11 mW cm^-2, and excellent stability at high current densities up to 100 mA cm^-2, surpassing commercial Pt/C. According to the density functional theory (DFT) study, the Co-N₄ moiety with graphitic N dopants can decrease the rate-determining step (RDS) energy barrier and thus accelerate the ORR process. This study offers experimental and theoretical guidelines for the rational design of TM-N-C catalysts for practical implementation with notable ORR activity for application in ZABs.

Key words: Single-atom electrocatalyst, Co-N₄ active sites, Oxygen reduction reaction, Zn-air battery, DFT study