High-capacity dual-electrolyte aluminum-air battery with circulating methanol anolyte

Abstract

Aluminum-air batteries (AABs) have recently received extensive attention because of their high energy density and low cost. Nevertheless, a critical issue limiting their practical application is corrosion of aluminum (Al) anode in an alkaline aqueous electrolyte, which results from hydrogen evolution reaction (HER). To effectively solve the corrosion issue, dissolution of Al anode should be carried out in a nonaqueous electrolyte. However, the main cathodic reaction, known as oxygen reduction reaction (ORR), is sluggish in such a nonaqueous electrolyte. Adual-electrolyte configuration with an anion exchange membrane separator allows AABs to implement a nonaqueous anolyte along with an aqueous catholyte. Thus, this work addresses the issue of anode corrosion in an alkaline Al-air flow battery via a dual-electrolyte system. The battery configuration consisted of an Al anode | anolyte | anion exchange membrane | catholyte | air cathode. The anolytes were methanol solutions containing 3 M potassium hydroxide (KOH) with different ratios of water. An aqueous polymer gel electrolyte was used as the catholyte. The corrosion of Al in the anolytes was duly investigated. The increase of water content in the anolyte reduced overpotential and exhibited faster anodic dissolution kinetics. This led to higher HER, along with a greater corrosion rate. The performance of the battery was also examined. At a discharge current density of 10 mA cm-2, the battery using the anolyte without water exhibited the highest specific capacity of 2328 mAh/gAl, producing 78% utilization of Al. At a higher content of water, a higher discharge voltage was attained. However, due to greater HER, the specific capacity of the battery decreased. Besides, the circulation rate of the anolyte affected the performance of the battery. For instance, at a higher circulation rate, a higher discharge voltage was attained. Overall, the dual-electrolyte system proved to be an effective approach for suppressing anodic corrosion in an alkaline Al-air flow battery and enhancing discharge capacity.