All protonated phosphonic acid membrane and ionomers for high powered intermediate temperature proton exchange membrane fuel cells

Fuel cells operating at intermediate temperature and low humidity conditions are a potential solution to overcome the drawbacks of both high and low temperature fuel cells for heavy duty transportation applications. Here, we report protonated phosphonic acid membranes that significantly increase the proton conductivity and durability of polymer electrolyte membrane fuel cells operating at intermediate temperatures and low humidity. The protonated phosphonic acid membrane with rigid aromatic polymers is an ideal strategy that utilizes the mixed vehicular and Grotthuss proton hopping ion conduction mechanisms of sulfonated and phosphonic acid polymers to increase proton conductivity and dimensional stability. By applying the protonated phosphonic acid system as both the membrane and ionomeric binder, fuel cell reached peak power densities of 0.51 W cm −2 at 120 °C and 40 % RH without leachable liquid phosphoric acid and demonstrated over 1000 h of onset voltage durability of 30.6 μV h −1 at 100 °C and 40 % RH conditions vastly outperforming perfluorinated membrane and ionomer combinations. • Polyphenylene protonated phosphonic acid membranes and ionomers were developed. • Intermediate temperature conductivities of membranes exceeded Nafion. • Intermediate temperature fuel cell performance reached 0.51 W/cm 2 at 120 °C, 40 % RH. • Developed membranes demonstrated over 1000 h durability at elevated temperatures.