Thermal Conductivity of Gas Diffusion Layers of PEM Fuel Cells: Anisotropy and Effects of Structures

When addressing the proton exchange membrane (PEM) fuel cells, effective water management is essential for the system to respond promptly to electric power demands. The local water vapor saturation pressure and interphase mass transfer are impacted by the temperature distribution inside the structure whereas the gas diffusion layer (GDL) is crucial in facilitating effective heat transfer during cell operation. This work is focused on obtaining a better understanding of the thermal conductivity (k) of the gas diffusion layer in two arrangements, single uncoated macro-porous layer GDL without polytetrafluoroethylene (PTFE), and as a coated double-layer consisting of GDL with 50 % PTFE and a micro-porous layer (MPL). The k in the in-plane and out-of-plane directions of the double-layer GDL improved by 50 % and 184 % in vacuum, respectively, compared with the case where it is uncoated and unsupported by MPL. Also, this study represents one of the first to investigate the k of double-layer GDL in the in-plane direction. Our out-of-plane k measurement in air and vacuum provides deep insight into the heat transfer mechanism of the porous GDL: the sample and pores inside it follow more parallel configurations than serial for the uncoated macro-porous layer sample, while quite serial configurations for the double-layer GDL sample.