Effect of PTFE and liquid water on the thermal characteristics of compressed gas diffusion backing of PEM fuel cell

Abstract

The thermal conductivity and thermal contact resistance (Rtc) of gas diffusion backing (GDB) play a key role in the distribution and transient of the temperature inside the proton exchange membrane fuel cell (PEMFC). In this paper, the layer-to-layer Rtc between GDBs is first tested by a series of comparative experiments, which is very small and almost negligible as the compression pressure is larger than 4.75 bar. Based on this, the through-plane thermal conductivity (kGDB) of GDB and the Rtc between GDB and test bench are determined. They are found to be the function of cyclic compression pressure, polytetrafluoroethylene (PTFE) content, and liquid water saturation. As the compression and load cycles increase, the value of kGDB increases, while Rtc decreases. Besides, the kGDB decreases with the increase of PTFE when the PTFE content is less than 20 wt%, but always increases with liquid water. At last, the Rtc between GDB and test bench increases with the increase of the PTFE content but firstly decreases dramatically with saturation, followed by slight changes as the saturation is above 0.1 because the pores in the interface region are fully filled with water. These findings can provide the thermal parameters for modelers to accurately predict the temperature profile inside PEMFC.