Article révisé par les pairs
Résumé : The coating technique and the type of carbon support can strongly affect the surface topography, the homogeneity and the thickness of the catalyst layers of Proton Exchange Membrane fuel cells. These features can in turn strongly modify the local diffusion properties of the layer and the final cell performance, but literature about catalytic layers does not often address such issues. This work aims at studying the topography of proton exchange membrane fuel cell catalyst layers by means of 3D characterization methods. For that purpose, two types of slurries, made of NafionⓇ and carbon black or a carbon xerogel, have been coated on a KaptonⓇ sheet by film-casting and by spray-coating. The surface topography of the samples was characterized by contact profilometry and 3D laser scanning microscopy. The data obtained with both methods were processed in order to obtain accurate 3D representations of the surface of the layers. Contact profilometry allows to perform measurements over the entire surface of the sample (5 cm × 5 cm). Layers obtained by film-casting turn out to be very smooth, but also thinner at the edges of the coating. For layers prepared by spray-coating, the reproducibility and the homogeneity are improved; however, the surface displays a higher roughness. With 3D laser scanning microscopy measurements, only a small part of the sample was analyzed (0.25 cm2) with a high definition, allowing to characterize more precisely the surface topography. The comparison of both techniques has been enriched by the simulation of the profilometer tip motion at the surface of the observed 3D microscopy profile, giving insight into the observed differences. The 3D microscopy measurements proved to be more accurate, but not representative of the whole sample, especially for less homogeneous layers prepared by film-casting.

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