Soluble Polystyrene‐b‐poly (ethylene/butylene)‐b‐polystyrene Based Ionomer for Anion Exchange Membrane Fuel Cells Operating at 70 °C

Abstract A soluble ionomer based on styrene‐ethylene/butylene‐styrene (SEBS) block polymer was synthesized with an ion exchange capacity (IEC) of 1.91 mmol g−1 and OH− ion conductivity at 100% relative humidity (RH) of 0.14 and 0.18 S cm−1 at 50 and 70 °C, respectively. The performance of the membrane electrode assembly (MEA) with SEBS ionomer was highest compared to polyvinyl benzyl chloride (PVBC) and Acta I2 ionomers at 0.5 V at both 50 °C (239 mW cm−2) and 70 °C (285 mW cm−2) using air and low‐density polyethylene (LDPE) membrane. This was largely due to the lower charge transfer resistance measured for the MEA using SEBS ionomer which is due to higher IEC, better water uptake and water retention properties. Ionomer water permeability is also critical for the back diffusion and the membrane where SEBS ionomer showed large advantage over PVBC ionomer. The long‐term testing of 50 h at 50 and 70 °C also showed better durability of the SEBS compared to the commercial Acta I2 ionomer with an average performance loss of 3 mA h−1 at 50 °C. The MEAs tested at 70 °C failed after 15 h (Acta I2) and 25 h (SEBS) due to pin‐hole formation in the membrane.