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.