Optimizing liquid free ionomer binders for high-temperature polymer electrolyte membrane fuel cells for heavy duty vehicles

Ionomer solutions LLC will develop membrane electrode assemblies (MEAs) that utilize high-temperature polymer electrolyte membranes (HT-PEMs) and ionomer electrode binders containing blends of poly(tetrafluorostyrene phosphonic acid) (PTFSPA) blended with perfluorosulfonic acid (PFSA) materials. The HT-PEM consists of a mixture of polycation-polybenzimidazole (PBI) and it uses electrostatic interactions to anchor phosphoric acid inside the polymer matrix. The HT-PEMs have an area specific resistance (ASR) of 0.035 Ω-cm2 at 120 °C/0% RH and an ASR of 0.07 Ω-cm2 at -40 °C. The HT-PEMs are stable over 100 hours at 180 °C in a fuel cell device. Using the polycation-PBI HT-PEM with the PTFSPA ionomer electrode binder led to a peak power density of 0.9 W cm-2 with hydrogen-oxygen at 220 °C. The new HT-PEMs were developed by PI Arges at Louisiana State University (LSU) and have a pending patent application. The technology is being transferred to Ionomer Solutions LLC - a Louisiana startup co-founded by PI Arges. In this project, Ionomer Solutions LLC will develop electrodes with state-of-the-art PGM electrocatalysts that feature a blend of ionomer electrode binders (PTFSPA combined with PFSA). State-of-the-art electrodes use PFSA type of binders but have yet to be paired with ion-pair HT-PEMs. Although 0.9 W cm-2 with hydrogen-air at 240 °C was achieved with PTFSPA binders and an ion-pair HT-PEM by Los Alamos National Laboratory, the power density reduced to 0.3 W cm-2 at 120 °C – which is the preferred operating temperature for fuel cell manufacturers developing heavy duty vehicles (HDVs). The project team hypothesizes that using a more oxygen permeable ionomer binder, such as PFSA as opposed to a hydrocarbon material like PTFSPA, will enhance power density at 120 °C. However, PFSA cannot be used solely in the electrode at 120 °C because of its poor conductivity under low RH/lack of condensed water. Blending PTFSPA into the electrode with a PFSA is posited to provide sufficient proton conduction at 40% RH or less while not hampering gas reactant mass transfer. Eliminating condensed water in the cell is also anticipated to achieve ambitious stability metrics required for HDVs. With the PFSA-PTFSPA ionomer electrode blends paired with the ion-pair HT-PEM, Ionomer Solutions LLC will improve HT-PEMFC power density so that the technology can eventually achieve the M2FCT 2025 MEA target of 2.5 kW gPGM-1 (1.07 A cm-2 @ 0.7 V, < 0.3 mgPGM cm-2).