Identifying contributing degradation phenomena in PEM fuel cell membrane electrode assemblies via electron microscopy

Advanced electron microscopy coupled with a unique ultramicrotomy specimen preparation technique have been used to characterize the network of microstructural assemblages within PEM fuel cell membrane electrode assemblies (MEAs) and to determine the roles of the different material constituents contributing to performance loss during fuel cell operation. Nanoscale structural and compositional analyses have been conducted on intact MEAs before and after electrochemical aging to identify the degradation of the individual constituents comprising the MEA, including: (1) electrocatalyst, (2) carbon catalyst support, (3) proton conducting membrane, and (4) re-cast ionomer. In the work presented here, Pt-based 3-layer MEAs were characterized 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. Several mechanisms contributed to performance loss, all of which could be correlated with the fresh MEA constituent morphology. Degradation occurred by a combination of catalyst particle coarsening, localized carbon corrosion, Pt dissolution and migration, and nm-scale membrane changes. The extent of each degradation mechanism depended on the aging conditions utilized. copyright The Electrochemical Society.