Buckling deformation of polymer electrolyte membrane and membrane electrode assembly under humidity cycles

Wrinkle deformations of both a polymer electrolyte membrane (PEM) and a membrane electrode assembly (MEA) under humidity cycles were analyzed. The NRE211 and NRE212 of commercial Nafion® were the PEMs used in this study. The MEA was composed of NRE212 and catalyst layers (CLs) between gas diffusion layers (GDLs) in a single cell and was exposed to 10 humidity cycles. The MEA deformed into a wrinkle shape at a width ranging between 330 and 500 μm. The compressive stress of the MEA under swelling was calculated using the MEA swelling ratio and Young's modulus, while the critical stress for the buckling of the MEA was estimated with Euler's in-plane buckling theory. By comparing these stresses, it was concluded that the MEA buckled under swelling. Moreover, the deformations of PEMs and MEAs against microscopic circular clearances under humidity cycles were analyzed. Both showed bulge deformations at clearances above each specific diameter, which can be estimated by the Euler in-plane buckling theory. Required PEM properties for preventing buckling are lower swelling ratios in the in-plane direction and thicker membranes. Additionally, a flat surface on the GDL is effective in preventing buckling. Preventing MEA buckling enables the long-term utilization of fuel cells.

► Wrinkle deformation of MEA occurred under humidity cycles.
► Bulge of MEA into microscopic holes was clarified after humidity cycles.
► In-plane buckling was caused, when clearance diameter exceeds the specific diameter.
► The clearance diameter can be estimated by Euler's in-plane buckling theory.