Transient Liquid Water Distributions in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers Observed through In-Operando Synchrotron X-ray Radiography

In this work, in-operando synchrotron X-ray radiography was used to capture the changes in the liquid water saturation of gas diffusion layers (GDLs) during changes in operating current density. Through in-operando visualizations at high temporal and spatial resolutions, we observed that the liquid water saturation increased with increasing current density. Eventually, a threshold water content in the GDL was reached despite further increases in current density. A time lag between the change in current density and the onset of increasing GDL water content was also observed. Current density consistently reached a steady state value before the GDL water content reached steady state, and the trends in liquid water distributions in the MPL were distinct from, yet influential to the accumulation in the substrate. We present a logarithmic growth function that describes the dynamic changes in GDL water content. The formulation of the GDL liquid water content transient response to changes in operating conditions provides a new metric for designing next generation fuel cell powertrains with fast dynamic responses. Through plane water thickness profiles were also used to show that the water accumulation patterns continued to evolve for up to 15 minutes at the low current density. (C) 2017 The Electrochemical Society.