Proton exchange membrane fuel cells (PEMFCs) are a progressive technology capable of providing on-demand energy without contributing to greenhouse gases. To meet the needs of transitioning from lab-scale fabrication to large-scale manufacturing, further analysis of catalyst layers is necessary. A common issue within the cathode catalyst layer (CL) is non-uniform distribution of the ionomer within the catalyst layer. Additionally, the interface between catalyst and ionomer is not well understood.

X-ray photoelectron spectroscopy (XPS) is a highly surface-sensitive technique primed to provide new insights into the challenging interfacial interactions and chemistries among the catalyst, support, and ionomer. Although Nafion is inherently susceptible to X-ray degradation, XPS can be used effectively through a modified acquisition strategy developed previously in our group. In this work, XPS has been used to probe CLs with focus on the catalyst-ionomer interface and interactions using a series of electrodes prepared by a Mayer rod coating method. The catalyst-ionomer interface was investigated as a function of support material, Pt loading on the support, and ionomer loading. Surface information was acquired using ex situ and in situ XPS to emphasize the evolution of this technique’s capabilities at probing ionomer interactions. Complementary characterization with scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDS) mapping of catalysts and electrode cross-sections were utilized to visualize distribution of catalyst, carbon, and ionomer in the CL to assist with interpretation of XPS data. Results from this dataset emphasize the potential of this technique to study complex interfaces in PEM catalysts layers motivating further work expanding to other catalysts and ionomers.