Bifunctional ligand Co metal-organic framework derived heterostructured Co-based nanocomposites as oxygen electrocatalysts toward rechargeable zinc-air batteries.

Rational construction of efficient and robust bifunctional oxygen electrocatalysts is key but challenging for the widespread application of rechargeable zinc-air batteries (ZABs). Herein, bifunctional ligand Co metal-organic frameworks were first explored to fabricate a hybrid of heterostructured CoOx/Co nanoparticles anchored on a carbon substrate rich in CoNx sites (CoOx/Co@CoNC) via a one-step pyrolysis method. Such a unique heterostructure provides abundant CoNx and CoOx/Co active sites to drive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. Besides, their positive synergies facilitate electron transfer and optimize charge/mass transportation. Consequently, the obtained CoOx/Co@CoNC exhibits a superior ORR activity with a higher half-wave potential of 0.88 V than Pt/C (0.83 V vs. RHE), and a comparable OER performance with an overpotential of 346 mV at 10 mA cm-2 to the commercial RuO2. The assembled ZAB using CoOx/Co@CoNC as a cathode catalyst displays a maximum power density of 168.4 mW cm-2, and excellent charge-discharge cyclability over 250 h at 5 mA cm-2. This work highlights the great potential of heterostructures in oxygen electrocatalysis and provides a new pathway for designing efficient bifunctional oxygen catalysts toward rechargeable ZABs.