Polymer electrolyte membrane fuel cell (PEMFC) performance and materials degradation, particularly associated with the cathode catalyst layer, can be directly attributed to the stability and durability, as well as the uniformity/homogeneity, of the individual material constituents comprising the membrane electrode assemblies (MEAs) e.g., electrocatalyst, catalyst support, and ionomer films, and the interfaces formed between these constituents. The structural and chemical homogeneity of the constituent materials and their interfaces within catalyst layers can be quantified via advanced electron microscopy methods. Ultimately, this microstructural evidence can be directly correlated with materials-specific degradation mechanisms that contribute to PEMFC performance loss, and can be used to identify potential processing variables that will improve the microstructure and compositional homogeneity within the electrode structure and enhance MEA durability and stability during operation. Research efforts at Oak Ridge National Laboratory are focused on the high-resolution microstructural and microchemical characterization of MEAs fabricated using different electocatalysts (Pt-based) and catalyst loadings, carbon-based support materials, and ionomer solutions, as well as the same MEAs subjected to accelerated stress tests (ASTs) designed to degrade specific MEA components. High-resolution analytical microscopy methods are used to directly image and map the distribution and chemistry of the various phases within catalyst layers, both on the micrometer-scale for assessing electrode through-thickness homogeneity and at the sub-Å-level to interrogate the individual constituents and the various interfaces formed. This presentation will focus on the application of advanced microscopy methods used to evaluate cathode catalyst layers before and after ASTs and how such methods can provide insight towards improved electrode design, durability, and performance.

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Research sponsored by (1) the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and (2) Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility.