Non-Fluorinated Sulfonated Poly(phenylene sulfone)-Based Polymers As Membranes and Binders in Proton Exchange Membrane Fuel Cells
Authors: Yazili-Marini Didem , Fogang Lionel Talley , Marini Emanuele , Titvinidze Giorgi , Hicke David , Bansmann Joachim , Joerissen Ludwig , Kreuer Klaus-Dieter 
Published: December 2024

Sulfonated poly-phenylene-sulfone (sPPS) polymers [1,2] are emerging as a promising alternative to traditional fluorinated membranes in proton exchange membrane fuel cells (PEMFCs), offering advantages such as lower gas crossover and reduced production costs. In addition, accelerated stress tests at open circuit voltage (OCV) demonstrate that sPPS membranes exhibit superior stability compared to perfluorosulfonic acid (PFSA) membranes under extreme conditions, such as 90°C and 30% relative humidity (RH) at 50 kPa
g
[3], and 80°C at 100% RH and 150 kPa
g
. Moreover, Figure 1a highlights that sPPS membranes, when used with PFSA-bonded electrodes, slightly outperform conventional PFSA membranes in terms of performance as well as maximum power density under the tested conditions. Notably, the area-specific resistance (HFR) recorded during the polarization curve is significantly lower than that of its PFSA counterpart. This is attributed to the exceptional high conductivity of sPPS membranes and their ability to be manufactured with thicknesses < 10 µm.

Our research extends their use in the catalyst layers of membrane electrode assemblies (MEAs). More specifically, we adopted two strategies to enhance the MEA performance: At the electrode architecture level, we varied the catalyst dispersion composition by adjusting the ionomer content and the nature of the solvent (see Figure 1b). At the electrochemical level, we optimized the break-in procedure. While no significant changes were observed with variations in solvent type and composition, modifications to the electrochemical break-in procedure significantly improved performance, as evidenced by an increase in the electrochemical active surface area. Figure 1c reveals that although cathodes bonded with sPPS experience initial kinetic losses at lower current densities, their performance gradually approaches that of PFSA-bonded electrodes at higher current densities. These initial kinetic losses are associated to interactions between platinum and sPPS, as identified through X-ray photoelectron spectroscopy (XPS).

In conclusion, sPPS polymers hold significant potential as both membranes and binders, paving the way toward reducing dependency on fluorinated compounds for more sustainable PEMFC.

References

[1] M. Schuster, K.-D. Kreuer, H.T. Andersen, J. Maier, Sulfonated Poly(phenylene sulfone) Polymers as Hydrolytically and Thermooxidatively Stable Proton Conducting Ionomers, Macromolecules 40 (2007) 598–607. https://doi.org/10.1021/ma062324z.

[2] M. Schuster, C.C. de Araujo, V. Atanasov, H.T. Andersen, K.-D. Kreuer, J. Maier, Highly Sulfonated Poly(phenylene sulfone): Preparation and Stability Issues, Macromolecules 42 (2009) 3129–3137. https://doi.org/10.1021/ma900333n.

[3] D. Yazili, E. Marini, T. Saatkamp, A. Münchinger, T. de Wild, L. Gubler, G. Titvinidze, M. Schuster, C. Schare, L. Jörissen, K.-D. Kreuer, Sulfonated Poly(Phenylene sulfone) blend membranes finding their way into proton exchange membrane fuel cells, Journal of Power Sources 563 (2023) 232791. https://doi.org/10.1016/j.jpowsour.2023.232791.

Figure 1