Poly(phenylene oxide)-Based Anion Exchange Membranes Having Linear Cross-Linkers or Star Cross-Linkers

Linear cross-linked and star cross-linked anion exchange membranes (AEMs) are reported in this work, namely, lcQPPO (linear cross-linked quaternized poly(2,4-dimethyl-1,4-phenylene oxide) (PPO)) and scDQPPO (star cross-linked quaternized PPO) . Compared with original quarternized PPO (QPPO), cross-linked AEMs show a restrained swelling degree. But, due to the hindrance of a cross-linking polymer matrix, lcQPPO membranes show decreased ionic conductivity. For scDQPPO, its wide and connective ion channels are beneficial to the conduction of OH–, exhibiting increased ionic conductivity. Besides, the aggregated and cross-linked polymer networks in scDQPPO enhance the chemical stability and mechanical properties of the AEMs. Specifically, for scDQPPO-40, a high OH– conductivity of 100.7 mS cm–1 and a low swelling degree of 20.7% are achieved at 80 °C. The tensile strength and elongation at break of wet scDQPPO-40 at 25 °C are 16.7 MPa and 18.0%. After immersing in 1 M NaOH at 80 °C for 30 days, the loss of ionic conductivity and weight for scDQPPO-40 is 24.2 and 14.8%, with the degradation of tensile strength and elongation at break of 22.2% and 26.7%, respectively. On the basis of the membrane, a fuel cell performance of 0.577 W cm–2 is demonstrated at 60 °C, while, for QPPO-40 and lcQPPO-60, their fuel cell peak power densities are only 0.250 and 0.215 W cm–2.