Aluminum-Air Batteries with Solid Hydrogel Electrolytes: Effect of pH Upon Cell Performance

The incorporation of aluminum anodes in metal-air galvanic cells is very interesting due to its intrinsic physico-chemical properties that include a high theoretical specific capacity (2.98 Ah g(-1)) compared to lithium (3.86 Ah g(-1)), low density, negative standard potential versus the standard hydrogen electrode (SHE), high abundance in the earth's crust, recyclability, and environmental friendliness. In this report, various hydrogels based on xanthan are described that were prepared at different pH values in order to produce solid electrolytes characterized by high ionic conductivity. These electrolytes have been characterized in aluminum-air galvanic cells using Pt/C based air cathodes. The performance of the cells was characterized by discharge tests performed at constant currents across the range from 3 to 6 mA/cm(2). The ability of recharging the cells was evaluated by determining the electrolyte electrochemical window using cyclic voltammetry (CV) measurements. The ionic conductivity of the hydrogels was determined by electrochemical impedance spectroscopy (EIS). The results evidenced the superior performance of acidic hydrogels in terms of cell capacity and anodic efficiency, due to the capability of xanthan as self-corrosion inhibitor, but the rechargeability was hindered because of the current consuming hydrogen reduction. A larger electrochemical window was observed for neutral hydrogels, but with low cell voltage, and by alkaline electrolytes, but at the expense of the anodic efficiency.

Automated summary

The use of aluminum anodes in metal-air galvanic cells shows promise due to its high theoretical specific capacity compared to lithium, recyclability, and environmental friendliness. The study focused on developing solid electrolytes based on xanthan hydrogels at different pH values to enhance cell performance. Acidic hydrogels demonstrated superior cell capacity and anodic efficiency, while neutral hydrogels had a larger electrochemical window with lower cell voltage, and alkaline electrolytes sacrificed anodic efficiency for a larger window.