Effect of polyelectrolyte architecture on chemical stability in alkaline medium of anion exchange membranes

The chemical stability of anion exchange membranes (AEM) is crucial for the durability of the electrochemical devices using them. In this context, poly(epichlorohydrin)-based AEM were subjected to chemical degradation in the presence of a corrosive alkaline medium. Linear and cross-linked polyelectrolytes grafted with ammonium cations based on Quinuclidine and/or DABCO were first synthesized. They were characterized by an IEC comprising between 1.3 and 3.1 mmol/g, an ionic conductivity above 2 mS/cm and transport numbers between 0.71 and 0.89. Their chemical stability was then evaluated after immersion in 1M to 8M KOH solutions for 672h at 50°C. The evolutions of these characteristics as well as the molecular structure of the materials during this period inform on the chemical resistance of the polymer backbone as well as that of the cationic sites. The main degradation reactions have been identified as chains scission and Hofmann elimination, leading to the loss of the cationic groups. Nevertheless, these reactions can be limited by a high crosslinking density of the membrane, enhancing then its chemical stability despite a high ammonium group content.