Porous nitrogen-doped carbon nanocages decorated with bimetallic iron/cobalt sites as superior oxygen catalysts for liquid and all-solid-state Zn–air batteries

Elaborate construction of advanced oxygen catalysts derived from metal-organic frameworks (MOFs) is urgently desired to fulfill the demands of highly efficient liquid and all-solid-state Zn–air batteries (ZABs). Herein, porous nitrogen-doped carbon nanocages decorated with bimetallic iron/cobalt sites (denoted as Co,Fe@NC-800) are elaborately fabricated by pyrolysis of a ZnCo-zeolitic imidazolate framework@Fe-histidine precursor at 800 °C. In this process, the dodecahedron skeleton of MOF is transformed into graphitized porous carbon nanocage, accompanied by effective modification of active bimetallic Co/Fe sites, while the thermal volatilization of low boiling metal Zn effectively creates numerous holes in the carbon layer. By virtue of bimetallic porous nitrogen-doped carbon nanocage, the optimized Co,Fe@NC-800 exhibits a positive half wave potential (E1/2 = 0.875 V) for oxygen reduction reaction (ORR). Consequently, the exceptional Co,Fe@NC-800 catalyst endows assembled liquid ZAB with a remarkable peak power density of 180 mW cm−2 and large specific capacity of 680 mAh gZn−1, and exhibits tremendous potentials in all-solid-state ZABs. Theoretical density functional theory calculations further disclose that the synergistic effect between N doping and bimetallic Co/Fe sites could significantly reduce the desorption energy barrier of *OH, and ultimately accelerate the kinetic process of ORR.