Effect of gas diffusion layer anisotropy on mechanical stresses in a polymer electrolyte membrane

Mechanical stresses arise in a polymer electrolyte fuel cell (PEFC) components since the polymer electrolyte membrane swells and shrinks with the change in hydration and these dimensional changes of the membrane are constrained by the cell assembly and the gas diffusion layers (GDLs). The carbon paper that is used as the GDL in PEFCs exhibits strong anisotropy due to the orientation of the fibers in the material. In this study, we investigate the role of GDL anisotropy on the stress distribution in a PEFC. A finite element model is developed to determine the mechanical stresses in a PEFC membrane. The impact of GDL anisotropy on the mechanical stresses in the membrane is emphasized and it is shown that isotropic mechanical properties lead to inaccurate stress predictions. Due to very low Young's modulus of the GDL in the through-plane direction (0.5 MPa) compared to its in-plane value (9 GPa), through-plane stresses induced in the membrane become negligible. The effects of the water content profiles on the stress distribution are also investigated and it is found that accurate description of water transport is critical for a reliable analysis of the hygral stresses.