MOF-derived nitrogen-doped carbon-based trimetallic bifunctional catalysts for rechargeable zinc-air batteries.

Zinc-air battery (ZAB) is a promising new metal-air energy system, but the large overpotentials of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) around the air electrode lead to their poor energy efficiency. Herein, a novel bifunctional oxygen electrocatalyst is reported with the preparation of a zeolite imidazolate framework (ZIF-67) derived trimetallic composites decorated nitrogen-doped carbon, which consist of NiFe alloy and Co nanoparticles. The ZIF-derived porous N-doped carbon shell can speed up the mass transfer efficiency. Whereas the electronic effect between the formed NiFe alloy and Co nanoparticles, as well as the N-doped carbon framework can enrich the active centers and enhance the electrical conductivity. As a result, the NiFe-Co@NC-450 catalyst shows superior performance manifested as a small potential gap (Δ E  = 0.857 V) between the overpotential at 10 mA cm -2 ( E j=10 ) for OER (460 mV) and half-wave potential ( E 1/2 ) for ORR (0.833 V). The liquid ZABs exhibit a high specific capacity reaching 798 mAh/g Zn and a stable cycling performance at 10 mA cm -2 for more than 200 h. Meanwhile, the NiFe-Co@NC-450 based flexible ZABs also presents robust flexibility and stability. This study has certain implications for the development of economical, powerful and stable bifunctional catalysts for ZABs.