Hollow Co/N-C@NiCo2O4 Spheres as Highly Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc–Air Batteries

In this paper, hollow Co/N-C@NiCo2O4 spheres assembled by nanoparticles were developed as efficient bifunctional catalysts for zinc–air batteries. The hollow structure is synthesized with ZIF-67 as a reactant template. NiCo-LDH grown on the ZIF-67 surface maintains its structural integrity during heat treatment and reduces the agglomeration of the material, which promotes charge transport during the catalytic process. The hollow structure has a specific surface area of 124.3 m2 g–1 with rich catalytic active sites. As expected, the power density of the Co/N-C@NiCo2O4-based Zn–air battery is 176 mW cm–2 and the specific capacity is 745 mAh g–1, with 1.45 V open-circuit voltage and 100 h cycling life, much better than those of the 20% Pt/C-RuO2-based Zn–air battery (1.42 V, 133 mW cm–2, 721 mAh g–1).