Modeling of wetting phenomena in cathode catalyst layers for PEM fuel cells

Abstract

Optimal water management in polymer electrolyte fuel cells hinges on understanding wetting phenomena inside the porous network of the cathode catalyst layer. Macrohomogeneous models have evolved to take into account water-related phenomena. However, existing modeling approaches implement a phenomenological description that employs a mixed wettability, thus neglecting vital structural features that constitute the wetting behavior. Other approaches exploit experimentally measured water retention curves to derive descriptors for the wetting properties of the catalyst material. Albeit, such measurements are scarce in the literature, elaborate and expensive, making a materials screening focused on wettability unfeasible. Our approach extends these efforts by providing a structure-based model that predicts water retention curves from catalyst layer ink parameters. The model accounts for structural formation at the ink stage and it captures the statistical distribution of wetting properties. Design trends derived on the basis of this model are in agreement with experimental findings in the literature. Furthermore, the model is analyzed for its implications on fuel cell degradation. Finally, we discuss its capabilities with regard to model-supported fuel cell design and optimization.