Thermal-Conductivity Characterization of Gas Diffusion Layer in Proton Exchange Membrane Fuel Cells and Electrolyzers Under Mechanical Loading

Abstract

Accurate information on the temperature field and associated heat transfer rates is particularly important for proton exchange membrane fuel cells (PEMFC) and PEM electrolyzers. An important parameter in fuel cell and electrolyzer performance analysis is the effective thermal conductivity of the gas diffusion layer (GDL) which is a solid porous medium. Usually, this parameter is introduced in modeling and performance analysis without taking into account the dependence of the GDL thermal conductivity λ (in W · m −1 · K −1 ) on mechanical compression. Nevertheless, mechanical stresses arising in an operating system can change significantly the thermal conductivity and heat exchange. Metrology allowing the characterization of the GDL thermal conductivity as a function of the applied mechanical compression has been developed in this study using the transient hot-wire technique (THW). This method is the best for obtaining standard reference data in fluids, but it is rarely used for thermalconductivity measurements in solids. The experiments provided with Quintech carbon cloth indicate a strong dependence (up to 300 %) of the thermal conductivity λ on the applied mechanical load. The experiments have been provided in the pressure range 0 < p < 8 MPa which corresponds to stresses arising in fuel cells. All obtained experimental results have been fitted by the equation λ = 0.9log(12 p + 17)(1 − 0.4e −50 p ) with 9 % uncertainty. The obtained experimental dependence can be used for correct modeling of coupled thermo/electro-mechanical phenomena in fuel cells and 123 1026 Int J Thermophys (2011) 32:1025-1037 electrolyzers. Special attention has been devoted to justification of the main hypotheses of the THW method and for estimation of the possible influence of the contact resistances. For this purpose, measurements with a different number of carbon cloth layers have been provided. The conducted experiments indicate the independence of the measured thermal conductivity on the number of GDL layers and, thus, justify the robustness of the developed method and apparatus for this type of application.

Numerical Study of the Dynamic Response of Heat and Mass Transfer to Operation Mode Switching of a Unitized Regenerative Fuel Cell

“…Hamour et al [35] adopted a transient model to investigate the heat conducting characteristics of the GDL for a PEM FC and a PEM EC. However, no article analyzing the heat response for URFCs has been found.…”

Methods to Measure the Electrical Resistances of a Gas Diffusion Layer Under Mechanical Compression

“…Then the current is applied between 1 and 4, and measured between 2 and 3, as in Figure 5 [54]. The sample undergoes the final application of a geometric correction factor [55].…”

Electrical conductivity of PEMFC under loading

“…The tested GDL material is used in fuel-cell applications because of its high porosity, good thermal and electrical properties [10]. This porous material has a fibber structure, Fig.…”

“…Such properties depend on the materials chosen and on the appropriate fabrication technology used [10].…”