Carbon-Free NiCo2O4-Based bifunctional Air Electrode for Metal-Air Battery Application

Abstract

The air cathode of an alkaline rechargeable metal-air battery typically contains carbon as the catalyst support. Unfortunately, carbon can be severely attacked by the highly reactive oxygen generated from the oxygen evolution reaction (OER) during charging, which limits the battery cycle life. To overcome this obstacle, it is imperative to develop carbon-free bifunctional air electrodes that exhibit improved stability and durability under charging and discharging. In this work, NiCo2O4 powders with a crystallite size from 5 to 190 nm were synthesized for preparation of carbon-free air electrodes for rechargeable metal-air battery cathode application. The unsupported, bifunctional, NiCo2O4-based electrodes exhibited reduced overpotentials for both oxygen evolution and reduction, compared to the carbon-based electrode. As the NiCo2O4 crystallite size decreased, the cycle life of the carbon-free electrode increased drastically, reaching over 100 successive, 0.5-h charge/discharge cycles at a current density of ±50 mA.cm-2 in a 6 M KOH electrolyte when the 5-nm spinel powder was utilized.