Measurement of through-plane effective thermal conductivity and contact resistance in PEM fuel cell diffusion media

An experimental study was performed to determine the through-plane thermal conductivity of various gas diffusion layer materials and thermal contact resistance between the gas diffusion layer (GDL) materials and an electrolytic iron surface as a function of compression load and PTFE content at 70 degrees C. The effective thermal conductivity of commercially available SpectraCarb untreated GDL was found to vary from 0.26 to 0.7 W/(m degrees C) as the compression load was increased from 0.7 to 13.8 bar. The contact resistance was reduced from 2.4 x 10(-4) m(2) degrees C/W at 0.7 bar to 0.6 x 10(-4) m(2) degrees C/W at 13.8 bar. The PTFE coating seemed to enhance the effective thermal conductivity at low compression loads and degrade effective thermal conductivity at higher compression loads. The presence of microporous layer and PTFE on SolviCore diffusion material reduced the effective thermal conductivity and increased thermal contact resistance as compared with the pure carbon fibers. The effective thermal conductivity was measured to be 0.25 W/(m degrees C) and 0.52 W/(m degrees C) at 70 degrees C, respectively at 0.7 and 13.8 bar for 30%-coated SolviCore GDL with microporous layer. The corresponding thermal contact resistance reduced from 3.6 x 10(-4) m(2) degrees C/W at 0.7 bar to 0.9 x 10(-4) m(2) degrees C/W at 13.8 bar. All GDL materials studied showed non-linear deformation under compression loads. The thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell. (C) 2009 Elsevier Ltd. All rights reserved.