Cobalt Oxide Nanoparticles/Nitrogen-Doped Graphene as the Highly Efficient Oxygen Reduction Electrocatalyst for Rechargeable Zinc-Air Batteries

Abstract

Environmentally friendly and inexpensive oxygen catalysts with high-efficient activity are paramount for powering zinc-air batteries. Here, cobalt oxide nanoparticles confined in nitrogen-doped graphene (CoO/NG) were produced as the oxygen reduction electrocatalyst for zinc-air batteries by hydrothermal and high-temperature calcination. During the hydrothermal process, the graphitic carbon nitride as the self-sacrificing template can be partially converted into a carbanion (CO32–) in the presence of cobalt-based ionic liquid ([N1444]Cl/CoCl2), which can generate cobalt carbonate (CoCO3) with Co2+. During the high-temperature calcination, CoCO3 is decomposed into CoO embedded into nitrogen-doped graphene and escaped CO2, which can increase specific surface areas of oxygen reduction electrocatalysts. The as-prepared CoO/NG shows not only abundant mesoporous structures but also large specific surface area. The CoO/NG exhibits outstanding oxygen reduction performance (E1/2 ≈ 0.830 V versus RHE). Additionally, the zinc-air battery manufactured by CoO/NG generates a specific capacity of 815.6 mA h g–1. It is verified that the CoO/NG catalyst as the air-cathode is promising in actual application of zinc-air batteries.