Substitution of Nafion with sulfonated polysulfone in membrane–electrode assembly components for 60–120°C PEMFC operation

To investigate the influence of sulfonated polysulfone (sPSU) in membrane–electrode assemblies (MEAs), sPSU-based gas diffusion electrodes (GDEs) and sPSU membranes were studied both as complete MEAs and as separate components in assembled MEAs at 60–120°C. The complete sPSU MEAs showed mass-transport limitations, irrespective of ion exchange capacity, compared to Nafion MEAs. Cyclic voltammetry and low-current impedance analysis revealed comparable electrochemically active catalyst areas and kinetic properties in the sPSU and Nafion GDEs, while gas-crossover measurements showed a lower gas permeability in sPSU compared to Nafion. The sPSU and Nafion GDEs, deposited on Nafion membranes, possessed comparable fuel cell characteristics at 120°C and 100% relative humidity, demonstrating no considerable limitations when utilizing sPSU as an alternative to Nafion in the GDE, thus implying a sufficient gas permeability in the sPSU GDE at high humidity. Furthermore, the results clearly showed that the sPSU membrane induced mass-transport limitations in both sPSU and Nafion GDEs, revealing that the limiting factor of the sPSU MEAs was primarily the membrane-induced cathode flooding due to unoptimized water transport in the sPSU membrane. The work demonstrates the importance of electrochemical evaluation of ionomers as complete MEAs and as separate components when studying MEAs.