Enriched sp2-Hybridized C Atoms toward the Tradeoff between Activity, Conductivity and Stability of Spherical Porous Metal–Nitrogen–Carbon Catalysts for Rechargeable Zinc–Air Batteries

Advances in high-performance transition-metal–nitrogen–carbon catalysts (M–N–Cs) for the oxygen reduction reactions (ORR) are high-profile efforts to realize the large-scale implementations of rechargeable zinc–air batteries. However, it is extremely desirable but challenging to achieve stable active sites and excellent electron transport capability for M–N–C catalysts. Herein, spherical porous M–N–Cs (denoted as NPCS-Fc) with tailoring of the sp2-C/sp3-C ratio in carbon shell were prepared from low-cost coal tar pitch (CTP) via an acid-treatment-introduced defect-assisted one-step pyrolysis strategy. Due to the tradeoff among activity, conductivity, and stability, NPCS-Fc exhibits excellent ORR performance with a half-wave potential (E1/2) of 0.863 V, a low Tafel slope of 59 mV dec–1, and long-cycle durability in alkaline media. As the air cathode, the assembled rechargeable zinc–air battery delivers a high OCV of 1.538 V and a specific capacity of 870 mAh gzn–1. The enriched sp2-C atom strategy to give M–N–C materials opens up a facile way for developing high-performance catalysts in flexible, rechargeable zinc–air batteries.