Effect of Humidification on the Ionomer-Catalyst Interactions of Sulfo-Phenylated Polyphenylene Ionomers in PEMFCs

Ionomer-catalyst interactions in polymer electrolyte membrane fuel cells (PEMFCs) are studied for sulfo-phenylated polyphenylene (sPPP) ionomers using CO displacement/stripping and oxygen (O 2 ) transport resistance. We find that sPPP ionomers demonstrate low sulfonic acid group adsorption on platinum (∼2%) at both dry and super-saturated humidities. This low ionomer adsorption appears to be driven by the ionomer’s strong swelling character with hydration, leading to ionomer detachment from the catalyst surface under these conditions. We also report that O 2 transport resistance is lower for electrodes containing sPPP ionomers by a factor of three compared to standard perfluorosulfonic acid (PFSA) ionomers. While PFSA thin films have been shown to rearrange over platinum sites, this effect may be limited in sPPP electrodes due to the rigidity of the backbone.