Adsorption Characteristics of Perfluorosulfonic Acid Membrane Decomposition Products on a Platinum Electrode: An EQCM Study

As hydrogen fuel cell vehicles move closer to mass commercialization, understanding the voltage losses due to contamination on low loading catalyst layers has become critical. It is imperative that contamination mechanisms are understood to mitigate these losses. In some cases, chemical breakdown of the polymer membrane can lead to formation of small molecules that can infiltrate and adsorb onto the catalyst layer, resulting in lower fuel cell performance and durability. Surface coverages of perfluorinated acid model compounds, representing polymer electrolyte membrane (PEM) chemical degradation products, were studied using an electrochemical quartz crystal microbalance (EQCM) with a polycrystalline platinum electrode. Perfluorosulfonic acid model compounds with a terminal sulfonic acid group exhibited no adsorption and no mass change. A similar model compound with a terminal carboxylic acid functional group exhibited higher surface coverage and stronger adsorption strength. Perfluorinated diacids, representing degradation products of a Nafion and 3M membrane, both showed mass increases well into the Pt oxide region, suggesting that the compounds were not fully displaced by surface oxides and that the terminal sulfonic acid group played a secondary role in the adsorption. Both perfluorinated chain length and functional group were found to play important roles in Pt surface adsorption characteristics.