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

Abstract

In this paper, hollow Co/N-C@NiCo 2 O 4 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 m 2 g −1 with rich catalytic active sites. As expected, the power density of the Co/N-C@NiCo 2 O 4based 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-RuO 2 -based Zn−air battery (1.42 V, 133 mW cm −2 , 721 mAh g −1 ).