Hydrolytic and alkaline stability of commercial and in-house anion exchange membranes

Some energy storage and conversion devices operating with alkaline electrolytes rely on anion exchange membranes (AEMs). However, their long-term performance remains limited by insufficient chemical and mechanical stability under operating conditions. In this context, this study investigates the stability of two commercial AEMs (PiperION and OrION) and two in-house membranes based on poly(epichlorohydrin) (PECH-PEO), with the aim of assessing their suitability for operation in alkaline electrolytes and in pure water, as encountered in water electrolysis. A comprehensive analysis of physicochemical and ionic properties was conducted during prolonged aging (up to 150 days) in KOH solutions of varying concentration (0-5 M) and temperature (40-80°C), as well as in water. While all membranes initially exhibited comparable electrochemical performance, their long-term stability strongly depended on the environment. Under alkaline conditions, PiperION and OrION undergo gradual degradation of their cationic sites, leading to a decrease in ion exchange capacity and ionic conductivity, whereas PECH-based membranes exhibit more severe degradation, including mass loss and loss of dimensional stability. In contrast, in hot deionized water, PiperION and OrION show unexpected and significant degradation, likely driven by radical-mediated mechanisms involving oxygen species, while PECH-based membranes display improved stability. These results highlight the critical influence of both the chemical structure and the counter-ion environment on anion exchange membrane durability. They demonstrate that membrane stability cannot be evaluated solely under alkaline conditions and emphasize the importance of considering water-induced degradation mechanisms.