In Situ EQCM‐D Investigations of PEMFC Catalyst‐Ionomer Interactions

Proton exchange membrane fuel cell (PEMFC) electrodes comprise multiple functional components whose interplay critically influences both performance and long‐term stability. In this article, the interaction between ionomer and catalyst materials was investigated using electrochemical quartz crystal microbalance with dissipation monitoring, enabling detection of potential‐dependent changes in mass and viscoelastic properties. Measurements were conducted on platinum, carbon, and gold electrodes, with and without a Nafion overlayer, in 0.5 M H 2 SO 4 and 0.1 M HClO 4 . Additionally, a representative catalyst layer (CL) was fabricated by spray‐coating PEMFC catalyst ink onto quartz crystals and examined under identical electrochemical conditions. Enhanced hydration of Nafion on a platinum electrode was observed during potential cycling, attributed to electrochemical reactions at the platinum surface, rather than being a direct consequence of the applied potential as this behavior was not observed on crystals with Nafion‐covered carbon electrodes. Changes in viscoelastic properties and mass uptake was shown to be influenced by the choice of electrolyte solution, particularly the nature of the anions. Importantly, the response of the spray‐coated PEMFC‐CL aligns closely with the behavior observed for Nafion‐coated planar platinum, validating the simplified model approach and providing deeper insight into ionomer behavior under dynamic fuel cell conditions.