Abstract
The effects of the thickness of thin electrodeposited palladium layers on the kinetics of hydrogen desorption processes are reported. Measurements have been performed with a piezoelectric quartz crystal microbalance under dynamic conditions, at a constant temperature of 61.1 ± 0.05 °C, and three different hydrogen-equilibrium pressures (α-phase region). From the kinetic analysis of desorption data, the desorption rate constants for the first-order step (k1d) and for the second order step (kIIdNeqi) have been calculated. The effect of the thickness of palladium layers is rather small in the first-order step, and very great in the second-order step. This behaviour is consistent with a mechanism which takes into account the adsorption of H atoms on two different surface states: (a) a weak adsorption (“pre-dissolved”) state, and (b) a strong adsorption state. The weight of the second- and first-order steps in the desorption process depends on the ratio of sites (a) to (b).
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