On the oxidation-reduction kinetics of palladium

The oxidation-reduction kinetics of Pd was investigated on polycrystalline Pd foils using XPS and sputter-depth profiling over a wide range of tempera tures. The observed behavior can be explained in terms of a desorption-cont rolled process at lower temperatures (T < 230 degrees C) and a diffusion-co ntrolled process at higher temperatures (T > 450 degrees C). In the interme diate range (230 < T < 450 degrees C) a transition between the two processe s is observed which gives rise to a pronounced shoulder in the reduction ti me trace. The interpretation is qualitatively confirmed using a simple math ematical model for a coupled bulk diffusion/surface reaction system.