A capillary water retention effect to improve medium-temperature fuel cell performance

•Morphology in sulfonated polymer membrane influences fuel cell performance at > 80 °C.•Morphology and hydrophilic domain size of three types of SPAES membranes were investigated.•G-SPAES shows excellent cell performance due to capillary water retention effect at 120 °C, 35% RH.

We demonstrate that small and narrow hydrophilic conducting domain morphology in sulfonated aromatic membranes leads to much better fuel cell performance at medium temperature and low humidity conditions than those with larger hydrophilic domains. A comparison of three types of sulfonated poly(arylene ether sulfone)s (SPAES) with random, block, and graft architecture indicates that small hydrophilic domain sizes (< 5 nm) appear to be important in supporting water retention under low relative humidity (RH) conditions intended for medium temperature (> 100 °C) fuel cell applications. The graft copolymer outperformed both a random copolymer and multiblock copolymer at 120 °C and 35% RH fuel cell operating conditions due to capillary condensation of water within the 3–5 nm hydrophilic domains.

Graphical abstractSmall hydrophilic domain sizes (< 5 nm) improve fuel cell performance due to capillary water retention effect at 120 °C, 35% RH.Figure optionsDownload full-size imageDownload as PowerPoint slide