Reinforced Polyphenylene Ionomer Membranes Exhibiting High Fuel Cell Performance and Mechanical Durability
Junpei Miyake, Takayuki Watanabe, Haruhiko Shintani, Yasushi Sugawara, Makoto Uchida, Kenji Miyatake
Abstract
We report on the preparation of reinforced membranes (SPP-QP-PE, where SPP stands for sulfonated polyphenylene), composed of an in-house proton-conductive polyphenylene ionomer (SPP-QP) and a flexible porous polyethylene (PE) mechanical support layer. By applying the push coating method, dense, uniform, transparent, and thin SPP-QP-PE membranes were obtainable. The use of SPP-QP with higher ion exchange capacity induced very high proton conductivity of SPP-QP-PE, leading to high fuel cell performance even at low humidified conditions (e.g., at 80 °C and 30% relative humidity), which had not been attainable with the existing reinforced aromatic ionomer membranes. The flexible porous PE substrate improved the mechanical toughness of the membranes; the elongation at break increased by a factor of 7.1 for SPP-QP-PE compared to that with the bare SPP-QP membrane, leading to mechanical durability at least 3850 wet-dry cycles under practical fuel cell operating conditions (the United States Department of Energy protocol). Overall, the reinforced aromatic ionomer membranes, SPP-QP-PE with balanced proton conductivity, mechanical toughness, and gas impermeability, functioned well in fuel cells with high performance and durability.