Fluorine-free sulfonated polyhedral oligomeric silsesquioxanes: replacing polymeric binder in fuel cell catalyst layers

One of the key points in transitioning to fluorine-free fuel cells is the development of fluorine-free ionomers for both membranes and electrodes. Promising materials, such as sulfonated phenylated polyphenylenes (sPPP) (e.g., Pemion®) and sulfonated polyphenylene sulfones (sPPS), demonstrate low gas crossover, making them suitable for membrane applications. However, recent studies suggest that their low gas permeability combined with high swelling under humid conditions complicates their use in electrodes, particularly at high current densities. In this study, however, we explore cage-like sulfonated polyhedral oligomeric silsesquioxanes (sPOSS) as a proton-conductive material and electrode binder. We demonstrate the fabrication of stable electrodes using sPOSS, which exhibit performance comparable to hydrocarbon-based ionomers like sPPP in the kinetic region while outperforming it at high current densities, likely due to improved gas transport properties.