Surface Properties of PEMFC Gas Diffusion Layers

Abstract

The wetting properties of proton exchange membrane fuel cell (PEMFC) gas diffusion layers (GDLs) were quantified by surface characterization measurements and modeling of material properties. Single-fiber contact-angle and surface-energy (both Zisman and Owens–Wendt) data of a wide spectrum of GDL types are presented to delineate the effects of hydrophobic postprocessing treatments. Modeling of the basic sessile-drop contact angle demonstrates that this value only gives a fraction of the total picture of interfacial wetting physics. Polar forces contributed less than dispersive forces to the composite wetting of GDLs. Internal water contact angles obtained from the Owens–Wendt analysis were measured at 13–19° higher than their single-fiber counterparts. An inverse relationship was found between internal contact angle and both Owens–Wendt surface energy and percent polarity of the GDL. The most sophisticated PEMFC mathematical models use either experimentally measured capillary pressures or the standard Young–Laplace capillary-pressure equation. Based on the results of the Owens–Wendt analysis, an advancement to the Young–Laplace equation was proposed for use in these mathematical models, which utilizes only solid surface energies and a fractional surface coverage of a fluoropolymer. Capillary constants for the spectrum of analyzed GDLs are presented for the same purpose.