Membranes from Poly(aryl ether)-Based Ionomers Containing Randomly Distributed Nanoclusters of 6 or 12 Sulfonic Acid Groups

Abstract

We report on the dependence of the properties on the morphologies of sulfonated polymers 3a and 3b (η inh = 0.65−1.18) with segments containing clusters of 6 and 12 sulfonic acid groups, respectively. The larger sulfonated clusters in polymers 3b resulted in higher proton conductivity and much better cell performance than polymers 3a . The highest power density of a fuel cell using 3a-1 (IEC = 1.16 mequiv/g) and Nafion 117 was 0.23 and 0.21 W/cm 2, respectively, at the effective work potential of 0.5 V, whereas that of 3b-1 (IEC = 1.16 mequiv/g) was 0.29 W/cm 2 at even higher effective work potential of 0.6 V. The morphological structure of 3a-1 and 3b-1 was investigated by transmission electron microscopy (TEM) and compared with that of Nafion. TEM images of 3a-1 and 3b-1 revealed a phase separation similar to that of Nafion, which may explain their higher proton conductivities compared to those of randomly sulfonated copolymers.