Alkyl-substituted poly(arylene piperidinium) membranes enhancing the performance of high-temperature polymer electrolyte membrane fuel cells

Abstract

Phosphoric acid-doped polybenzimidazole (PA-doped PBI) membranes enable high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) to operate at elevated temperature (140–180 °C), with the advantages of simplified water/heat management. However, the relatively long start-up time and insufficient performance due to the introduction of the liquid phosphoric acid electrolyte are still major barriers to the application of HT-PEMFCs. Herein, a series of alkyl-substituted poly(arylene piperidinium) membranes are designed to modulate the content and distribution of phosphoric acid, which significantly reduces the ohmic and mass transfer resistance and boosts the performance of HT-PEMFCs in a wide operational temperature range. By tailoring the pendant alkyl groups of the piperidinium cations, the steric hindrance around the piperidinium cations and the free volume of poly(arylene piperidinium) can be well regulated. The optimized isobutyl-substituted poly(arylene piperidinium) membrane shows a high acid doping level (10.05) and a relatively high proton conductivity. As a result, a PEMFC based on this membrane shows significantly low ohmic and mass transfer resistances, consequently enhancing the peak power density of the HT-PEMFC to >1.5 W cm⁻² at a moderate temperature of 120 °C under H₂/O₂ conditions.