Soft X-ray visualization of the liquid water transport within the cracks of micro porous layer in PEMFC

In order to investigate the effect of the cracks on the MPL on liquid water transport, the cross-sectional imaging (cell membrane parallel to the beam) of liquid water behavior in the operating PEMFC was carried out by laboratory-based soft X-ray radiography technique. The spatial and temporal resolutions of the visualization were 0.5 um and 2 s/frame, respectively. The carbon cloth GDLs with the cracked MPL were used and each layer of the PEMFC and the crack on the MPL were clearly visualized. The results clearly showed that the liquid water mainly flows through the crack on the MPL to the substrate layer, and no liquid water was observed in the MPL. Because the MPL is highly hydrophobic, the MPL can limit the liquid water access to the substrate layer. On the other hand, liquid water tends to be stored in the interface between the CL and the MPL. These results suggest that the larger pores (e.g. cracks) on the MPL function as the liquid water pathway to the substrate layer, and the smaller pores on the MPL function as the gas transport path, and the surface morphology of the MPL might affect the liquid water transport in the PEMFC.

Research highlights
► Liquid water behavior in the PEMFC was visualized by soft X-ray radiography.
► High resolution imaging realized the visualization of water accumulation behavior.
► Liquid water tends to be stored in the interface between the CL and MPL.
► The cracks on the MPL function as the liquid water pathway to the substrate layer.
► The surface morphology of the MPL strongly affect the liquid water transport in the PEMFC.