(Co,Fe)(3)O-4 Decorated Nitrogen-Doped Carbon Nanotubes in Nano-Composite Gas Diffusion Layers as Highly Stable Bifunctional Catalysts for Rechargeable Zinc-Air Batteries

(Co,Fe)(3)O-4 nanoparticles are decorated onto N-doped carbon nanotubes at room temperature through a simple mixing process and are simultaneously deposited within a porous gas diffusion layer (GDL) by an impregnation technique. The (Co,Fe)(3)O-4 nanoparticles are identified as the spinel phase through transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. The composite GDL is used as the air electrode for Zn-air batteries and shows excellent performance as a bifunctional catalyst with initial discharge and charge potentials of 1.19 V and 2.00 V, respectively, at 20 mA cm(-2). Cycling performance of the impregnated electrode compares favourably with benchmark Pt-RuO2 catalysts at both 10 mA cm(-2) and 20 mA cm(-2). The (Co,Fe)(3)O-4/N-CNT impregnated GDL had a final discharge/charge efficiency of 58.5 % after 100 h (200 cycles) of bifunctional cycling at 10 mA cm(-2), which is superior to that of Pt-RuO2 (55.3 % efficiency). The cycling efficiency for (Co,Fe)(3)O-4/N-CNT impregnated GDL at 20 mA cm(-2) is also better than that for Pt-Ru (53.5 % vs 41.3 % after 50 h (100 cycles)). The result is a simple and easily scalable one-pot electrode synthesis method for high performing bi-functional air electrodes for Zn-air batteries.