Densely atomic Co–Nx moiety-coupled hierarchical-carbon-microspheres for efficient oxygen electrodes in bioadaptable Mg–air batteries†

The Mg–air battery is one of the promising candidates for the next generation of bioadaptable power sources. However, it suffers from low efficiency cathodes to facilitate the slow oxygen reduction reaction (ORR). Herein, this work reports a strategy to enhance the density of catalytic active sites and further facilitate their accessibility for advanced air electrodes. A prior spray-assisted stepwise pyrolysis strategy is employed to obtain the densely atomic Co–Nx active site-decorated hierarchically carbon microspheres (Co–Nx–HCM), which are further employed as advanced oxygen electrodes for primary Mg–air batteries. The resulting Co–Nx active sites impart electrodes with good bio-adaptability and decent ORR activity under neutral electrolytes. Furthermore, the hierarchical carbon microspheres endow the air electrode with smooth mass transport. In application of an assembled Mg–air flow battery, the SA Co–Nx–HCM electrode delivers a high open-circuit potential of 1.78 V, a high maximum power density of 34.2 mW cm⁻², a decent gravimetric energy density of ca. 3441 Wh kg_Mg⁻¹, and a long operating life over 100 h. This work paves a way to explore single atomic catalysts with hierarchically porous morphology as advanced air cathodes for bioadaptable electronic devices.