Investigation of the effect of a hydrophilic layer in the gas diffusion layer of a polymer electrolyte membrane fuel cell on the cell performance and cold start behaviour

The effect on PEFC performance of a gas diffusion layer (GDL) with a hydrophilic layer (HL) between the microporous layer (MPL) and the carbon paper (CP) was investigated at high and low humidity at normal operating temperatures and at subfreezing temperatures. Scanning electron microscopic examination and micro-Raman spectroscopic examination were carried out on the three-layer structure (MPL, HL and CP). In addition, high magnification SEM images of the samples showed that the HL had smaller pores than the MPL of the HL-GDL. Thus, we consider that the capillary pressure in the pores of the HL was higher than that in the MPL of the HL-GDL, which suggests that the HL can absorb more water. The performances of cells using the GDL with or without a HL were compared. The cell using a GDL with a HL showed a higher performance than a cell with a conventional GDL in the high current density region at both high and low humidity. At high humidity, the HL can absorb generated water, improving water removal from the catalyst layer (CL) to the GDL, and inhibiting the stoppage of gas diffusion by condensed water in the CL. At low humidity, the HL enhanced the water retention in the MEA, inhibiting the decrease of proton conductivity of the electrolyte by dehydration. A cell using a GDL with a HL also showed superior performance during cold startup from -10 °C, due to water removal by the HL, inhibiting the blockage of gas diffusion by condensed or frozen water in the CL. These results indicate that an HL placed between the MPL and the carbon paper of the GDL can improve the PEFC performance over a wide range of operating conditions, including high and low humidity at normal temperatures and cold startup from subfreezing temperatures.