Chloride-driven construction of Zn-N/Cl and Co-N/Cl/Co-Co dual active sites in hollow porous carbon nanofibers for durable zinc-air batteries

A NaCl/ZnCl 2 -assisted electrospinning-pyrolysis strategy was developed to fabricate Zn/Co/Na codoped hollow porous carbon fibers (ZnCoNa-CFs) as efficient bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries. During pyrolysis, salt-assisted carbon framework reconstruction and pore evolution generated an interconnected hollow porous architecture favorable for mass transport and exposure of catalytically relevant sites. Meanwhile, distinct Zn- and Co-containing coordination environments, including highly dispersed Zn–N/Cl-coordinated species and Co–N/Cl-coordinated species accompanied by Co–Co-containing domains, were formed within the carbon matrix. Benefiting from the integration of the hierarchical porous architecture and complementary metal coordination environments, ZnCoNa-CFs exhibited excellent oxygen reduction reaction (ORR) activity with a half-wave potential of 0.88 V and a low Tafel slope of 50.7 mV dec −1 , outperforming commercial Pt/C. For oxygen evolution reaction (OER), only 1.59 V was required to achieve 10 mA cm −2 , with a Tafel slope of 96.3 mV dec −1 , comparable to or better than commercial RuO 2 . Electrochemical comparisons, poisoning experiments, and theoretical calculations associate the Zn-containing environments predominantly with ORR and the Co-containing environments with OER, supporting their complementary contributions to bifunctional oxygen catalysis. Furthermore, rechargeable liquid and flexible zinc-air batteries assembled with ZnCoNa-CFs delivered high peak power densities of 163.9 mW cm −2 and 150.7 mW cm −2 , respectively, along with stable operation exceeding 2000 h and 160 h. This work demonstrates an effective strategy for integrating chloride-regulated Zn/Co coordination environments with hierarchical carbon architectures toward high-performance noble-metal-free bifunctional electrocatalysts for rechargeable zinc-air batteries.