The kinetics of hydrogen (deuterium) sorption by thin palladium layers studied with a piezoelectric quartz crystal microbalance

Abstract

The kinetics of the hydrogen (deuterium) Sorption processes in the α-phase region of a thin electrodeposited Pd layer (thickness 3 × 10 −5 cm) are reported. Measurements have been performed with a piezoelectric quartz crystal microbalance using an AT-cut crystal with a resonance frequency f 0 q = 5.27 MHz and a sensitivity of ∼10 10 digits g −1, at a constant temperature 80.3 ± 0.05 °C and different pressures. Both the absorption and the desorption of H 2(D 2) on Pd layers are controlled successively by a chemisorption step (second order kinetics) in the early stage of the processes and by a surface migration step (first order kinetics), in the subsequent stage of the processes. Consistent with the reported piezoelectric quartz crystal microbalance measurements, thermal desorption and electrochemical desorption studies, a mechanism is suggested which takes into account the adsorption ofH(D) atoms on two different surface states: (a) a “pre-dissolved” state which does not depend on the surface nature; (b) and adsorption state, the density of which depends upon the structure and nature of the Pd sample. The kinetic control of the entire processes (sorption and desorption) depends on the ratio of the density of sites (a) to (b).