Measurement of capillary pressure in fuel cell diffusion media, micro-porous layers, catalyst layers, and interfaces

In this work, semi-empirical Leverett J-Function relationships relating capillary pressure and water saturation are experimentally derived for commercial and experimental polymer electrolyte fuel cell materials developed for automotive applications. Relationships were derived for Mitsubishi Rayon Corp. (MRC) U105 and General Motors (GM) experimental high tortuosity diffusion media (DM), the micro-porous layer (MPL), and the catalyst layer (CL). The standard Leverett J-Function under-predicted drainage curves for the DM at high saturation levels and significantly under-predicted the capillary pressure requirements for the MPL and CL across the entire saturation range. Composite structures were tested to understand interfacial effects for DM|MPL and MPL|CL. Each additional layer was found to superimpose its effects on capillary pressure onto the previous layers. The MPL formulation tested increased in porosity from a 136 nm peak average to a 153 nm peak average with increased surface porosity of the substrate. Additionally, small voids and pockets that accumulate liquid water were found to exist in the MPL|CL interface. The results of this work are useful for computational modelers seeking to enhance the resolution of their macroscopic multi-phase flow models which underestimate capillary pressure using the standard Leverett J-Function.