Rotating disk electrode measurements on low and high loading catalyst layers: Diffusion limitations and application to Pt catalysts supported on porous micrometric carbon xerogel particles designed for proton exchange membrane fuel cells

Innovative fuel cell catalysts are now often being supported on nanostructured materials in order to improve mass transport, contact with the ionomer and active phase distribution. However, to maintain their inner struc-ture, these supports are used as mu m-sized particles, which hampers to perform accurate kinetic experiments on rotating disk electrode since a thin layer of catalyst is in principle required. The present study thus aims at checking if accurate measurements remain possible for thick layers of large particles. To do so, oxygen reduc-tion was first performed on a commercial Pt catalyst supported on carbon black; both a typical thin and a thick layer (37 and 370 mu gPt cm-2) were used. The impact of the diffusion limitations on the kinetic current was determined. The same measurement protocol was then performed with a catalyst supported on 5 mu m particles of a nanostructured carbon (similar to 15 mu m layer thickness, 370 mu gPt cm-2). Results and calculation show that, for both thick layers, the kinetic current should be measured at higher potential (1.00 or 1.05 V/ESH) than usual to avoid diffusion limitations. Also, the voltage scanning rate should be lowered to 0.5 or 1 mV s-1 to decrease the impact of the double layer capacity on the measurements.