Simultaneous characterization of oxygen transport resistance and spatially resolved liquid water saturation at high-current density of polymer electrolyte membrane fuel cells with varied cathode relative humidity

In this study, the impacts of relative humidity on liquid water accumulation and mass transport resistance at high current densities were investigated for polymer electrolyte membrane (PEM) fuel cell cathode gas diffusion layers (GDLs). Through-plane liquid water saturation distributions were measured in situ using synchrotron X-ray radiography while simultaneously performing limiting current-based characterizations of oxygen transport resistance. In experiments with inlet cathode reactant relative humidity ranging from 0% to 100%, high local saturations (>0.6) were consistently observed in the GDL region adjacent to the flow field lands when the fuel cell reached limiting current. High land-region saturation is a possible indication of lower local temperatures. In the carbon fiber substrate portion of the GDL (i.e. excluding the MPL), the liquid water volume in the regions adjacent to the flow field channels was consistently small relative to the water volume adjacent to the land regions. We observed a trend of increasing liquid water saturation of the GDL adjacent to the channels with increasing levels of cathode inlet relative humidity, along with corresponding small increases in total oxygen transport resistance.