Dynamic characterization of partially saturated engineered porous media and gas diffusion layers using hydraulic admittance

• Published in: Journal of power sources 2012-09, Vol.214, p.266-276
• Main Authors: Cheung, Perry, Fairweather, Joseph D., Schwartz, Daniel T.
• Format: Article
• Language: English
• Subjects: Admittance; Applied sciences; Capillary pressure measurements; Computational fluid dynamics; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical impedance; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fluid flow; Fuel cells; Gas diffusion layers; Hydraulic admittance measurements; Hydraulics; Interfacial resonance; Liquid water distribution; Mathematical models; Polymer electrolyte membrane fuel cells; Saturation; Spectra
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2012.04.088

Simple laboratory methods for determining liquid water distribution in polymer electrolyte membrane fuel cell gas diffusion layers (GDLs) are needed to engineer better GDL materials. Capillary pressure vs. liquid saturation measurements are attractive, but lack the ability to probe the hydraulic interconnectivity and distribution within the pore structure. Hydraulic admittance measurements of simple capillary bundles have recently been shown to nicely measure characteristics of the free-interfaces and hydraulic path. Here we examine the use of hydraulic admittance with a succession of increasingly complex porous media, starting with a laser-drilled sample with 154 asymmetric pores and progress to the behavior of Toray TGP-H090 carbon papers. The asymmetric laser-drilled sample clearly shows hydraulic admittance measurements are sensitive to sample orientation, especially when examined as a function of saturation state. Finite element modeling of the hydraulic admittance is consistent with experimental measurements. The hydraulic admittance spectra from GDL samples are complex, so we examine trends in the spectra as a function of wet proofing (0% and 40% Teflon loadings) as well as saturation state of the GDL. The presence of clear peaks in the admittance spectra for both GDL samples suggests a few pore types are largely responsible for transporting liquid water. [Display omitted] ► Performed hydraulic admittance on engineered porous sample with over 100 pores. ► Hydraulic admittance of engineered sample matched predicted simulation response. ► Performed hydraulic admittance on 2 GDL samples at different saturation states. ► Hydraulic admittance spectra of GDL samples show expected frequency dependence. ► Distinct resonance peaks show finite number of pores transport liquid water in GDL.