Fuel cells with an operational range of –20 °C to 200 °C enabled by phosphoric acid-doped intrinsically ultramicroporous membranes

Conventional proton exchange membrane fuel cells (PEMFCs) operate within narrow temperature ranges. Typically, they are run at either 80‒90 °C using fully humidified perfluorosulfonic acid membranes, or at 140‒180 °C using non-humidified phosphoric acid (PA)-doped membranes, to avoid water condensation-induced PA leaching. However, the ability to function over a broader range of temperature and humidity could simplify heat and water management, thus reducing costs. Here we present PA-doped intrinsically ultramicroporous membranes constructed from rigid, high free volume, Tröger’s base-derived polymers, which allow operation from −20 to 200 °C. Membranes with an average ultramicropore radius of 3.3 Å show a syphoning effect that allows high retention of PA even under highly humidified conditions and present more than three orders of magnitude higher proton conductivity retention than conventional dense PA-doped polybenzimidazole membranes. The resulting PA-doped PEMFCs display 95% peak power density retention after 150 start-up/shut-down cycles at 15 °C and can accomplish over 100 cycles, even at −20 °C. Most proton exchange membrane fuel cells are designed to operate within a temperature range of a few tens of degrees, but functioning in a broader range of conditions could be advantageous. Here the authors use ultramicroporous, phosphoric acid-doped membranes that allow fuel cell operation from −20 °C to 200 °C.