A universal procedure to prepare high density M-N sites anchored in nitrogen doped porous carbon as efficient oxygen reduction reaction catalysts for flexible Zn-air batteries.

Developing single-atom catalysts (SACs) with dense active sites and universal synthesis strategies remains a critical challenge. Herein, we present a scalable and universal strategy to synthesize high-density transition metal single-atom sites, anchored in nitrogen-doped porous carbon (M-SA@NC, M = Fe, Co, Ni) and investigate their oxygen reduction reaction (ORR) catalytic activity for flexible Zn-air batteries (ZABs). Using a facile coordination-pyrolysis strategy, atomically dispersed M-N sites with high metal loading are achieved. Systematic characterizations confirm the highly dense planar FeN configuration and abundant micropores, which collectively enhance ORR kinetics. The Fe-SA@NC catalyst exhibits a remarkable half-wave potential of 0.89 V for ORR, and demonstrates a four-electron pathway with negligible HO yield. When integrated into ZABs, Fe-SA@NC delivers a high open-circuit voltage of 1.57 V and a high-power density of 184.1 mW cm. In addition, its performance is also not affected by bending in flexible ZABs. The universality of this method is validated by extending it to Co-SA@NC and Ni-SA@NC, all showing competitive ORR activity. This work provides a generalizable platform for designing high-density SACs and paves the way for their application in next-generation wearable energy devices.