Ex-situ visualization of the wet domain in the microporous layer in a polymer electrolyte fuel cell by X-ray computed tomography under water vapor supply

Abstract

The wet domain in a microporous layer (MPL) in a polymer electrolyte fuel cell (PEFC) was visualized in order to clarify water accumulation in the MPL. The performance of PEFC is affected by accumulation of liquid water in the cathode gas diffusion layer (GDL). The liquid water hinders oxygen transport to the catalyst layer, resulting in increased mass-transport loss. Although MPLs suppress water accumulation in the GDL, this mechanism has not yet been fully clarified. The present study used synchrotron X-ray micro computed tomography (CT) to visualize water accumulation in the MPL. The experiment was conducted while supplying water vapor to the MPL side of the GDL. The MPL was visualized to be wetted heterogeneously, and liquid water movement from the MPL to the GDL substrate was visualized. These observations were supported by plotting the volume fraction of either the wet domain of the MPL or the water cluster as a function of through-plane distance.