Determination of the porosity and its heterogeneity of fuel cell microporous layers by X-ray tomographic microscopy

Advancing polymer electrolyte fuel cell technology includes the rational design of the microporous layer (MPL) coating on the gas diffusion layer (GDL), where the porosity and morphology on an operation-relevant size scale are still largely undetermined and hinder further developments. Here, 15 commercially available GDLs with MPL coatings from three major manufacturers (seven Freudenberg, four Sigracet (R) SGL and four CeTech materials) were characterized by X-ray tomographic microscopy. An extensive set of structural parameters for the MPLs are presented, including MPL total porosity, microporosity, porosity heterogeneity and thickness heterogeneity. The analyses show that the CeTech GDLs tend to have MPLs with the lowest porosity, while the Sigracet (R) GDLs have MPL with the highest porosity. Furthermore, Freudenberg H23 materials have the lowest porosity heterogeneity, and the Freudenberg CX materials' porosity are most heterogeneous. Many of the commercial MPLs, expected to be homogeneous, show a gradient of MPL microporosity in the thickness direction. The characterized MPLs are classified into five distinct classes based on thickness and porosity heterogeneities. This classification and the detailed data presented support the understanding of fuel cell performances with different MPL types. The comprehensive set of data also serve as realistic input values for material and fuel cell modeling studies.

Automated summary

This study characterizes the structural parameters of microporous layer (MPL) coatings on gas diffusion layers (GDLs), including porosity and thickness heterogeneity. The results show that MPLs from different manufacturers exhibit different properties. Additionally, many commercial MPLs display a porosity gradient in the thickness direction.