Gas-diffusion layer's structural anisotropy induced localized instability of nation membrane in polymer electrolyte fuel cell

摘要

The design of robust polymer electrolyte fuel cell requires a thorough understanding of the materials' response of the cell components to the operational conditions such as temperature and hydration. As the electrolyte membrane's mechanical properties are temperature, hydration and rate dependent, its response under cyclic loading is of significant importance to predict the damage onset and thus the membrane lifetime. This article reports on the variation in stress levels in the membrane induced due to the gas-diffusion layer's (GDL) anisotropic mechanical properties while accurately capturing the membrane's mechanical response under time dependent hygrothermomechanical conditions. An observation is made on the evolution of negative strain in the membrane under the bipolar plate channel area, which is an indication of membrane thinning, and the magnitude of this strain found to depend upon the GDL's in-plane mechanical properties. In order to come up with a strategy that reduces the magnitude of tensile stresses evolved in the membrane during the hygrothermal unloading and to increase the membrane's lifetime, we numerically show that by employing a fast hygrothermal loading rate and unloading rate strategy, significant reduction (in this study, nearly 100%) in the magnitude of tensile stresses is achievable. The present study assists in understanding the relation between materials compatibility and durability of fuel cell components.