Capillary pressure and hydrophilic porosity in gas diffusion layers for polymer electrolyte fuel cells

Abstract

Capillary pressure versus saturation curves for drainage of a wetting phase were measured for several gas diffusion layers that are commonly used in polymer electrolyte membrane fuel cells. The technique employed can measure capillary pressure curves for both the total pore network and the pore network consisting of only hydrophilic pores. This enables the determination of capillary pressure curves directly relevant to the study of gas diffusion layer flooding. The overall distributions compared well with mercury intrusion data. It was found that the pore size distribution for the hydrophilic pores were similar in shape to the overall distribution for standard substrate materials. Materials with a microporous layer did not follow this trend and the microporous layer was found to be completely hydrophobic. Due to their similarity, the overall and hydrophilic capillary pressure curves for all materials could be correlated using a single Leverett J-function. The results were described by several standard capillary models, the parameters of which can be further used to predict the relative permeability of the phases.