Performance Decay of Air Electrode Configuration for Rechargeable Zinc-Air Batteries.

The construction of the air electrode structure is critical in the rechargeable zinc-air batteries. So far, the majority of previous articles have been reported on the process in boosting electrocatalytic bifunctional oxygen reaction activity. Nevertheless, the reason that caused the deterioration of air electrodes has been rarely investigated, which dramatically influences cell performance. Herein, self-supported MnO₂ bifunctional electrocatalysts on nickel foam are integrated with the gas diffusion layer to form air electrodes. The charge voltage of the as-prepared electrode used in rechargeable zinc-air battery is reduced by 1.82% and the discharge voltage is decreased by 5.25% after 1000 cycles at the current density of 20 mA cm⁻² under the mode of 5 min charge and 5 min discharge, which demonstrate the feasibility of the novel electrode structure design. Besides, The X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) were conducted to analyze the change of composition, structure, and performance. The origin of the decrease of the discharge profile was analyzed. Experimental studies revealed that the main cause of voltage loss is mainly attributed to the destroyed gas diffusion structure (at large current densities) and the activation loss of MnO₂ caused by the (oxy)hydroxide film (at small current densities). The destroyed gas diffusion structure gives rise to the poor oxygen transfer and further water flooding due to the formation of large pore caused by oxygen evolution in the charging process and increased hydrophilicity by the carbon oxidation. Meanwhile, the film growing overtop of the electrocatalysts would result in mass transfer and activation losses. [ABSTRACT FROM AUTHOR]