Crucial role of side-chain functionality in anion exchange membranes: Properties and alkaline fuel cell performance

Side-chain functionality is critical to achieve highly conductive and chemically stable anion exchange membrane (AEM) materials. Herein, two series of quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) having different lengths (n or m) of cationic side-chains were designed and prepared, including PPO-C-nQA with a triazole-containing linker and PPO-mQA without triazole groups in the side chains. The effect of the side-chain functionality on the properties of AEMs has been systematically investigated. Long cationic side chains in PPO-mQA membranes induced the formation of obvious microphase-separated morphology. However, PPO-C-nQA membranes with a triazole-containing linker showed a considerable higher hydroxide conductivity than that of PPO-mQA membranes, due to the developed hydrogen-bond networks between triazole and water/hydroxide. High retention of conductivity and low degree of crosslinking were observed for the AEMs with longer side-chains (PPO-C-3QA, PPO-C-4QA, PPO-6QA, and PPO-7QA) in the alkaline stability testing under 10 M NaOH at 80 °C for 250 h, indicating their excellent stability. Moreover, a single H2/O2 AEMFC with these side-chain type AEMs demonstrated that PPO-C-1QA with highest conductivity exhibited a peak power density of 141.3 mW cm−2 at a current density of 320 mA cm−2.