Liquid Water Visualization in the Pt-Loading Catalyst Layers of Polymer Electrolyte Fuel Cells Using Operando Synchrotron X-ray Radiography

Water management is important for addressing the challenges posed by next-generation fuel cell electric vehicles. Although X-ray imaging techniques are useful for probing the mechanism of water transport in the gas diffusion layer of polymer electrolyte fuel cells, they cannot be easily applied to the Pt-loading catalyst layer because of its low X-ray transmittance due to the high absorption coefficient of Pt. Herein, we propose a method to realize the high-resolution X-ray imaging of the cathode catalyst layer in polymer electrolyte fuel cells using synchrotron X-ray radiography, thus bridging the above gap. The results of operando synchrotron X-ray radiography measurements reveal that water accumulation in the cathode catalyst layer depends on the cell temperature, feed gas humidity, and cell voltage, while time-slice analysis shows that the water accumulation rate in the cathode catalyst layer is approximately four times that in the cathode gas diffusion layer. The proposed imaging method can be used to evaluate the water uptake capability of the catalyst layer and thus deepen our understanding of flooding phenomena and cold-start behavior at subzero temperatures.