Membranes for alkaline water electrolysis and flow batteries

Abstract

In electrolysers, AEM are in contact with hot water. We show stress-strain tests in temperature-controlled water, analyze how temperature affects the membrane dimensions, and present a simple method to measure the true hydroxide conductivity of AEM in temperature-controlled water.[1] To minimize dimensional changes during cell assembly (dry membrane) and start of operation (wet membrane), we propose to pre-swell AEM with high boiling point solvents. Ethylene glycol-swollen membranes can be handled without dimensional changes during cell assembly, and only swell marginally when the electrolyser is filled with water or KOH solution.[2] An alternative to AEM are ion-solvating membranes. We developed porous PTFE-supported polybenzimidazole gels. In comparison to state-of-the-art KOH doped PBI membranes, which fail rapidly in alkaline electrolysers, the reinforced gel PBI membranes were successfully tested for 1,000 hours without failure, at a performance similar to PEM water electrolysers.[3] In vanadium redox flow batteries, gel PBI was used to stabilize 2 ？m thin dense PBI selective layers. Thhis combination allowed to reach an excellent energy efficiency of 90.5%.[4]