Enhancement of oxygen diffusivity in gas diffusion layer of PEFC with wettability distribution and effect of PTFE content

Abstract

The mass transfer characteristics of the gas diffusion layer (GDL) are closely related to cell performance in polymer electrolyte fuel cell (PEFC). Thus, it is necessary to clarify the characteristics of liquid water distribution, microscopic conformation and the oxygen diffusivity in the GDL. In the present study, a hybrid type GDL is prepared using carbon paper GDL with a non-uniform wettability distribution to control the liquid water movement in the GDL and achieve both oxygen diffusion and moisture retention. To improve the oxygen diffusion characteristic of the previous reported hybrid GDL, hybrid type GDLs with different hydrophobic regions and different PTFE contents were fabricated. The effects of the different hydrophobic regions and PTFE content on the oxygen diffusivity and liquid water distribution were simultaneously measured using a galvanic cell type oxygen absorber and X-ray radiography using the BL20B2 beamline at SPring-8. In the result, the formation of oxygen diffusion paths was visualized; the pores in the hybrid GDL were formed from the hydrophobic regions, and the pores spread to the untreated region that was not hydrophobized (hydrophilic region) after the formation of the initial pores. Thus, the formation of oxygen diffusion paths enhanced the oxygen diffusivity. Additionally, the examination of effects of the hydrophobic region and PTFE content in the GDLs indicated the optimal amount of PTFE for a hybrid GDL.