N,O symmetric double coordination of an unsaturated Fe single-atom confined within a graphene framework for extraordinarily boosting oxygen reduction in Zn-air batteries

The Fe-N coordinated single atom catalysts (SACs) are regarded as one of the most prominent substitutes for the commercial Pt/C electrocatalyst in the oxygen reduction reaction (ORR) of zinc-air batteries (ZABs). Nevertheless, precisely regulating the coordination configuration of Fe sites to enhance the catalytic performance of SACs remains elusive. Herein, we develop an innovative configuration of N,O symmetric double-coordinated Fe single atoms confined in a graphene framework (Fe-N,O/G) with coordinatively unsaturated (CUS) Fe sites for a highly active and durable ORR electrocatalyst in Zn-air batteries. The as-designed catalyst achieves efficient ORR activity by regulating the coordination environment of Fe single atoms, delivering a positive half-wave potential of 0.86 V. Moreover, the constructed Zn-air battery based on the Fe-N,O/G catalytic cathode achieves a peak discharge power density of 164.7 mW cm(-2) and a discharge stability of >150 h at 20 mA cm(-2), which exceeds that of the Pt/C catalyst. Theoretical calculation results demonstrate that the fine structure of N,O symmetrical coordination is beneficial to enhance the conductivity and activity for facilitating the 4-electron transport process during the ORR. This work enriches the system of regulating the coordination environment of SACs to boost the catalytic performance.