Effect of local stress concentration near the rib edge on water and electron transport phenomena in polymer electrolyte fuel cell

The performance of polymer electrolyte fuel cell (PEFC) depends on transport phenomena in the gas diffusion layer (GDL). To elucidate the relationship between the local stress concentration near the rib edge and current density distribution, contact stress analysis and charge transport calculations were performed. Subsequently, the effect of GDL deformation caused by the local stress concentration on water transport was investigated. As a result, contact stress analysis showed that through-plane stress in GDL was concentrated near the rib edge. However, the stress was not concentrated on the catalyst layer even when the compression ratio and curvature radius of the rib were varied over a wide range. By solving the charge conservation equation, the potential and current density distribution were obtained. The current density, although not concentrated on the catalyst layer, was concentrated in GDL near the rib edge because the GDL conductivity near the rib edge increased locally from the stress concentration. Calculation showed that to decrease the effect of local stress, rounding off the rib is more effective than decreasing the compression ratio. From scanning electron microscopy (SEM) images of the GDL after clamping, the stress concentration caused the breakup of fibers and polytetrafluoroethylene (PTFE), which caused the hydrophobicity to deteriorate. Therefore, the preferential pathways of water behavior were observed near the rib edge. It was shown that local stress concentration near the rib edge affected the water behavior and GDL characteristics although it did not affect the catalyst layer.