| Proton exchange membrane fuel cells (PEMFCs) are high-efficiency low-temperature power sources under development for a range of applications. The effective management of liquid water within a PEMFC stack remains an area of intense interest for enabling higher power density and more robust operation for fuel cell systems. One of the greatest challenges for improving water management through component design is a quantitative understanding of the role of capillary forces within the macroporous gas diffusion layers (GDLs).;This work presents a custom tool suitable for measuring the hysteretic capillary pressure vs. saturation (PC-SL) relationship in the thin fibrous media used for PEMFC GDLs. This PC-SL relationship is critical for modeling transport processes through a PEMFC system, and provides valuable quantitative comparisons between alternative GDL structures and treatments. Water/air PC-SL measurements are combined with mercury intrusion porosimetry (MIP), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and cyclic voltammetry (CV) to provide a thorough characterization of GDL samples. The effect of fluoropolymer wetproofing treatment is analyzed, and the common assumption of a mixed hydrophobic/hydrophilic pore structure is challenged. A simple bundle-of-capillaries model is used to calculated effective contact angles, suitable for pore-level simulation of multiphase flows. Finally, wetting changes over fuel cell lifetime are examined, after both in-situ durability experiments and ex-situ rapid aging tests. |
