Characteristics of oxygen diffusivity and water distribution by X-ray radiography in microporous media in alternate porous layers of different wettability for moisture control in gas diffusion layer of PEFC

The mass transfer characteristics of the gas diffusion layer (GDL) are closely related to the performance of polymer electrolyte fuel cells. This study investigates the configuration of a new GDL in which two porous media with different wettabilities are alternately arranged (hybrid GDL). The oxygen diffusivity characteristics with respect to water content (saturation) were measured using an experimental system that employs a galvanic oxygen sensor as an oxygen absorber. Furthermore, X-ray radiography was used to observe the internal water distribution in microporous media for GDL to elucidate the enhancement mechanisms of oxygen diffusivity of the new microporous media. It was possible to distinguish between voids and water in microporous media by using X-ray computer tomography. In addition, the water distributions in the new microporous media were visualized and the mechanisms for the high oxygen diffusivity of the hybrid structure of microporous media were clarified.

► The “hybrid GDL”, in which the alternative arrangement of two porous media with different wettability were proposed for moisture control in gas diffusion layer of PEFC. ► The hybrid GDL successfully showed better oxygen diffusivity than single configuration. ► X-ray tomography visualization in hybrid type microporous media confirmed that liquid water was preferentially discharged through the hydrophilic layer.