Single-atom Co-N4 catalytic sites anchored on N-doped ordered mesoporous carbon for excellent Zn-air batteries

Abstract

• Co-SA/N-C 900 was synthesized via in-situ pyrolysis of co-precursors containing sucrose, dicyandiamide, and Co salt without additional acid etching and pyrolysis activation. • The large specific surface area and an ordered mesoporous structure endow the accessibility of active sites. • Atomic Co-N 4 catalytic sites with adjacent graphitic N dopants can boost the intrinsic activity of the obtained catalyst. • Co-SA/N-C 900 exhibits an onset potential of 0.96 V and a half-wave potential of 0.87 V, outperforming commercial Pt/C. 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-C 900 , 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-N 4 moiety. Co-SA/N-C 900 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-C 900 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-N 4 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. Co-SA/N-C 900 possesses atomic Co-N 4 moiety with graphitic N dopants, a large specific surface area, and an ordered mesoporous structure simultaneously, which is conducive to the accessibility of reactant molecules towards the active sites for more efficient mass transfer during the electrocatalytic process, exhibiting efficient ORR activity and Zn-air battery performance.