Time-resolved X-ray computed tomography of wetting at the outer surface of the microporous layer in a polymer electrolyte fuel cell

This study presents time-resolved X-ray computed tomography (CT) measurements to investigate the wetting and water discharge behavior of the microporous layer (MPL) in a gas diffusion layer (GDL) used in polymer electrolyte fuel cells. To simulate the condensation of water vapor generated in the catalyst layer, we cooled the substrate side of the GDL using a Peltier device, allowing water vapor that had diffused into the MPL to condense into liquid. The resultant time-resolved CT images showed the dynamic evolution of wet domains in the MPL. The wet fraction of the MPL reached a steady state, whereas the water accumulation continued to progress both on the MPL outer surface and in the substrate side. Classification of wet domains on the basis of their connectivity revealed that domains connected to the outer surface of the MPL serve as persistent discharge pathways of the liquid water from the MPL. • Time-resolved X-ray CT visualized water accumulation/discharge in the MPL of a GDL. • The water saturation of the MPL reached a steady state of 12 %. • Wet domains connected to the outer MPL surface acted as discharge pathways. • 21 % of the MPL surface remained continuously wet; certain regions were never wet.