Molecular weight impacts the alkaline stability of poly(terphenylene alkylene) anion exchange membranes

Improving the alkaline durability is crucial for developing anion exchange membranes used for electrochemical energy devices. In contrast to the exploitation of new cationic moieties or robust polymer backbone, the influence of polyelectrolyte molecular weight on the membrane's alkaline stability has received little attention. In this contribution, quaternized poly(terphenylene alkylene)s with Mw ranging from 30 to 118 kDa were synthesized to quantify the variations in alkaline stability and other physicochemical properties. Measurements of ex-situ alkaline soaking, either in high or low hydration levels, and in-situ cell operating demonstrate that Mw is positively correlated to the alkaline stability of the membrane. In addition, the water absorption and ion conductivity of AEM are negatively correlated to its Mws, and incline to reach a plateau as the Mw over 100 kDa. These results have important implications to elucidate the alkaline stability limitation and may open the way toward highly stable AEMs.