(119b) Microstructural Characterization of Life-Limiting Membrane-Electrode-Assembly Materials Degradation Phenomena

Advanced electron microscopy coupled with a unique ultramicrotomy specimen preparation technique are being used to characterize the network of microstructural features within PEM fuel cell membrane electrode assemblies (MEAs) and to determine the roles of the material constituents contributing to performance loss during PEM fuel cell operation. Atomic-level structural and compositional analyses have been conducted on intact MEAs before and after life-testing to identify the degradation of the individual constituents comprising the MEA, including: (1) electrocatalyst (2) carbon catalyst support (3) proton conducting membrane (4) re-cast ionomer. In the work to be presented, Pt- and Pt-alloy-based 3-layer MEAs were characterized primarily by transmission electron microscopy (TEM). The MEAs were characterized in the fresh (as-processed) condition and then subjected to an extensive matrix of aging conditions to evaluate the effects of temperature, humidity, and potential cycling on the MEA constituent stability. Degradation occurred by a combination of catalyst particle coarsening, localized carbon corrosion, Pt dissolution and migration, and nm-scale membrane changes, and these observations will be described in detail.