The oxidation-reduction kinetics of Pd was investigated on polycrystalline Pd foils using XPS and sputter-depth profiling over a wide range of temperatures. The observed behavior can be explained in terms of a desorption-controlled process at lower temperatures (T < 230°C) and a diffusion-controlled process at higher temperatures (T > 450°C). In the intermediate range (230 < T < 450°C) a transition between the two processes is observed which gives rise to a pronounced shoulder in the reduction time trace. The interpretation is qualitatively confirmed using a simple mathematical model for a coupled bulk diffusion/surface reaction system.
- Reaction-diffusion model
- Sputter-depth profiling