Cobalt Oxide\nNanoparticles/Nitrogen-Doped Graphene\nas the Highly Efficient Oxygen Reduction Electrocatalyst for Rechargeable\nZinc-Air Batteries

Abstract

Environmentally friendly and inexpensive oxygen catalysts\nwith\nhigh-efficient activity are paramount for powering zinc-air batteries.\nHere, cobalt oxide nanoparticles confined in nitrogen-doped graphene\n(CoO/NG) were produced as the oxygen reduction electrocatalyst for\nzinc-air batteries by hydrothermal and high-temperature calcination.\nDuring the hydrothermal process, the graphitic carbon nitride as the\nself-sacrificing template can be partially converted into a carbanion\n(CO₃^2–) in the presence of cobalt-based\nionic liquid ([N₁₄₄₄]­Cl/CoCl₂), which can generate\ncobalt carbonate (CoCO₃) with Co²⁺. During the\nhigh-temperature calcination, CoCO₃ is decomposed into\nCoO embedded into nitrogen-doped graphene and escaped CO₂, which can increase specific surface areas of oxygen reduction electrocatalysts.\nThe as-prepared CoO/NG shows not only abundant mesoporous structures\nbut also large specific surface area. The CoO/NG exhibits outstanding\noxygen reduction performance (<i>E</i>_1/2 ≈\n0.830 V versus RHE). Additionally, the zinc-air battery manufactured\nby 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\nin actual application of zinc-air batteries.