Probing the Catalyst-Ionomer Interface in Catalyst Layers with Sulfo-Phenylated Polyphenylene Ionomers Using CO-Displacement and Stripping Techniques

Abstract

An investigation of ionomer-catalyst interfaces for electrodes containing sulfo-phenylated polyphenylene (sPPP) ionomers is conducted with CO displacement and stripping experiments. We find that at fully humidified conditions, catalyst layers containing sPPP ionomers show a CO displacement peak that is almost entirely suppressed. This suppression corresponds to adsorption of sulfonic acid group adsorption on only 2% of the available Pt surface. We also observe that at 100% RH, the double-layer capacitance of the catalyst layer is higher when poisoned by CO. This is inverse of the behavior observed with PFSA electrodes, indicating that there might be different ionomer-catalyst interactions present with an sPPP ionomer. We hypothesize that differences between sPPP and perfluorinated sulfonic acid (PFSA) ionomer backbones may account for this difference due to the presence of phenyl rings, which could adsorb to Pt surfaces preferentially at high humidification.