One-dimensional transient model for frost heave in polymer electrolyte fuel cells

To better understand, control, and mitigate degradation during freezing of a polymer electrolyte fuel cells (PEFCs), a one-dimensional (1D) transient model has been formulated, based on theories of porous media flow and soil frost heave. The model is essentially a modified hybrid of Harlan's hydraulic model and Miller's rigid ice model with additional improvements for suitable application to PEFCs. It is found that the three types of characteristic curves for unfrozen water flow and frost heave modeling can be well unified. Methods to derive the unfrozen water vs temperature characteristic curves for PEFC components are also given. Through the formulated model, it is predicted that ice lens will occur most likely around the catalyst layer, either between catalyst layer and diffusion media, or between catalyst layer and Nafion membrane. Lens formation under the lands is unlikely due to high overburden pressure. Ice lens growth may explain breakthrough observed in carbon paper after freeze-thaw tests. Another phenomenon, the delamination between Nafion and catalyst layer, can possibly be explained by the formation of an ice lens from water expelled from the electrolyte during freezing. The Nafion thickness and initial water content have direct impact on the damage in this mode.