Influence of sulfone linkage on the stability of aromatic quaternary ammonium polymers for alkaline fuel cells

The properties and stability of quaternary ammonium poly(sulfone) QA-RADEL and quaternary ammonium poly(phenylene oxide) QA-PPO were investigated. These two membranes have a major difference in their backbone structure where QA-RADEL contains an electron-withdrawing group and QA-PPO is an ether-based backbone without electron-withdrawing group in the main chain. Conductivity, thickness and swelling measurments were examined at various temperatures for both types of samples. HRSEM and FTIR analysis indicated that QA-RADEL membrane degraded much faster than QA-PPO under high temperature and high pH conditions. QA-RADEL showed degradation at both the cationic groups and the polymer backbone after 150 h at 60°C, while QA-PPO showed degradation merely at the cationic groups after aging for 1000 h at 60°C, under high pH conditions. The sulfone linkage has a profound negative influence on the thermal and alkaline stability of the membrane, which provides design rules for future high-stability AEMs.