From –20 to 200 °C: Fuel Cells with Broad Operational Flexibility Enabled by Intrinsically Ultramicroporous Membranes

Conventional proton exchange membrane fuel cells (PEMFCs) operate at a narrow temperature range, either under low temperature conditions (80‒90°C) using fully-humidified perfluorosulfonic acid (Nafion®) membranes or under non-humidified high temperature conditions (140‒180°C) using phosphoric acid (PA)-doped membranes to avoid water condensation-induced PA leaching. To allow wide operational flexibility over the full spectrum of temperature and humidity ranges, we present an innovative design strategy by using PA-doped intrinsically ultramicroporous membranes constructed from rigid and contorted high free volume polymers. The membranes with an average ultramicropore radius of 3.3 Å showed a significant siphoning effect as confirmed by the delocalization of PA in 31P NMR, thus allowing high retention of PA even under highly humidified conditions and presenting more than three orders of magnitude higher proton conductivity retention than conventional dense PA-doped polybenzimidazole membranes (PBI/PA). The resulting PEMFCs display impressive performance over a much broader temperature range from − 20 to 200°C and can accomplish over 100 start-up/shut-down cycles even at − 20°C. The broad operational flexibility rendered from the high PA-retention can ultimately simplify heat and water management and thereby reduce PEMFC costs.