Electrode binder design for high-power, low-Pt loading and durable high temperature fuel cells

Abstract

State-of-the-art high-temperature polymer electrolyte membrane fuel cells enabled by the phosphoric acid-doped polybenzimidazole material platform are promising for long-haul transport, but suffer from low output power, low Pt utilization, and rapid phosphoric acid loss under harsh/dynamic operating conditions. Here, we report a multifunctional phosphonated ionomeric binder (PFPA-PIM-SBI), derived from polymers of intrinsic microporosity, that addresses the above issues. Covalently bonded pentafluorophenyl phosphonic acid groups enhance proton conductivity, and the highly contorted molecular configuration of PFPA-PIM-SBI could prevent the undesirable adsorption of phenyl groups on the Pt catalyst, while frustrated polymer chain packing affords high microporosity for fast mass transport of gases and products. They combine to contribute to high-performing H₂/O₂ fuel cells, with a high Pt utilization of around 50%, a peak power density of >1000 mW cm⁻² at 240 °C and a high Pt mass-specific peak power density of 6.4 W mg_Pt⁻¹ at an ultralow Pt loading of 0.07 mg cm⁻². We disclose that the atypical phosphoric acid wettability of PFPA-PIM-SBI can prevent the migration of phosphoric acids to the electrode and the subsequent loss, accompanied by the inhibition of anhydride formation, enabling long-lifetime fuel cells at ultralow Pt loadings or under accelerated stress tests.