Characterization of the Micro Porous Layer - Catalyst Layer Interface Structure in Polymer Electrolyte Fuel Cells

The impact of interfacial contact between the catalyst layer (CL) and diffusion medium (DM) has important implications for the transport of heat, current, and multi-phase flow in the membrane electrode assembly. This work is motivated by the need to obtain a greater understanding of the impact of the micro porous layer (MPL) and CL morphologies and resulting interfacial contact on the fuel cell performance. In this effort, an array of different virgin mating CL and MPL surface structures was investigated. The mating surface morphology of the tested MPL and CL samples were digitally characterized by optical profilometry, a non-destructive imaging technique which measures the 3-D surface topology of samples with a resolution on the order of several nanometers in the vertical direction, and 0.5 to 5 microns in the lateral direction. The benchmark data were utilized in an analytical model developed for virtual reconstruction of a compressed interfacial structure. The results show that for the materials tested, the MPL surface exhibits a higher degree of roughness compared to catalyst surfaces. The MPL surface was observed to have relatively higher roughness than the CL, indicating the potential dominance of the MPL surface morphology on the local transport and interfacial contact across the MPL|CL interface. Elasticity, compression, and uncompressed surface morphology are the key factors controlling the ultimate interfacial contact.