Amorphous zeolite imidazole framework-derived hierarchically porous and multi-catalytic active site bifunctional catalysts for zinc-air batteries

Zeolitic imidazolate frameworks (ZIFs) are widely used as cathode catalysts of zinc-air batteries (ZABs) due to their ultra-high porosity and abundant metal-N-C structure. However, the microporous structure of ZIFs prevents the catalytic potential from being well utilized. Herein, a hierarchically porous CoFe alloy-embedded metal-nitrogen-doped carbon (CoFe@HP/CoNC) bifunctional catalyst is prepared. Amorphous ZIF-67 forms a hierarchically porous structure by embedding nanoscale NaCl templates. The CoFe alloy site is derived from a strategy of introducing secondary metal ions. Thanks to the specifically porous structure and the CoFe alloy sites, the produced catalyst exhibited efficient bifunctional catalytic activity with a half-wave potential of 0.864 V (vs. RHE) for the oxygen reduction reaction (ORR) and an overpotential of 310 mV for the oxygen evolution reaction (OER) at a current of 10 mA cm-2. The CoFe@HP/CoNC-based ZAB showed an excellent power density (221.3 mW cm-2), a remarkable specific capacity (760.7 mAh gZn-1) and superb durability of more than 450 h/900 cycles at 5 mA cm-2. This work provides a simple strategy for the design of non-precious metal bifunctional electrocatalysts, which is expected to satisfy the practical application requirements of zinc-air batteries and other energy conversion and storage devices. Hierarchical porous Co-NC compounds embedded with CoFe alloys were successfully synthesized by a facile salt template-assisted strategy and exhibited excellent catalytic activity and durability as bifunctional oxygen catalysts for zinc-air batteries.