Highly Conductive Quaternary Ammonium-Free Membranes Showing Stable Performance for Water Electrolysis in 1 M KOH

Abstract

Anion exchange membrane water electrolysers (AEMWE) represent the latest advancement in hydrogen production technology, offering numerous advantages over its predecessors. However, commercialization is impeded by the low alkaline stability of most AEMs, attributed to the fragility of quaternary ammonium groups. [1] Ion solvating membranes (ISM) may serve as a viable alternative; however, its utilization needs high alkaline concentrations, because conductivity of state-of-the-art membranes decreases strongly below concentrations of 3 M KOH. In this work,[2] an ISM based on sulfonated para-polybenzimidazole was fabricated. Owing to the presence of sulfonic acid groups, this ISM exhibits significant swelling in 1 M KOH, attaining a conductivity exceeding 100 mS cm-1. Furthermore, the absence of quaternary ammonium groups and crosslinking with dibromoxylene resulted in excellent alkaline stability. Conductivity, tensile strength, and Young's Modulus of membrane with 5wt% DBX (5’MS-PBI) remained high after 6 months of stability test in 1 M KOH at 80 °C. In comparison, four commercial AEMs lost the majority of their conductivity after 30 days. [3] The electrolyser performance test operating with 1 M KOH at 80 °C was stable without failure for over 500 hours, suggesting that the high alkaline stability observed in ex-situ tests is also achieved in the electrolyser. In conclusion, the use of ISM potentially opens a pathway towards durable AEMWE systems.