Catalyst layer cracks by buckling deformation of membrane electrode assemblies under humidity cycles and mitigation methods

• Catalyst layer cracks occurred by a bulge deformation of membrane electrode assemblies with repeated humidity cycles.
• Formation of catalyst layer cracks was delayed in lower clearance heights.
• In FEM simulation, larger stresses happened in the region of the CL crack occurrence in the experiments.
• An in-plane swelling of the PEM was reduced in lower clearance heights.

In this study, the formation of catalyst layer (CL) cracks in a membrane electrode assembly (MEA) under multiple humidity cycles is analyzed to propose solutions to mitigate the crack formation. The MEA is fabricated by the thermal transfer of catalyst layers (4 μm thickness) to both sides of the NR211 (25 μm thickness). The buckling deformations are created by microscopic 300 μm diameter holes in the polyimide (PI) films. The microscopic holes model the clearance between the MEA and gas diffusion layers (GDLs). The clearance height is adjusted by the film thickness. The MEA and PI film are sandwiched between the GDLs and exposed to humidity cycles in test cells. When the clearance height decreases, the CL cracks do not tend to develop after repeated humidity cycles. In the FEM analysis, swelling of the NR211 causes large plastic strains on the CL in areas that correspond to crack locations in the experiment. For the lower clearance heights, the plastic strain in the CL is reduced due to reduction of the in-plane swelling ratio of the NR211 as it swells. A reduction in in-plane swelling of the PEM by thoughtful structure design is directly effective in preventing CL cracks as well.