Characteristics of hydrogen sorption/desorption for palladium foil doped by yttrium

Abstract

Kinetics of hydrogen adsorption and desorption for palladium- 7% yttrium foil was studied using volume metrics measurements in oil free vacuum cell. Preliminary H2 was purified by diffusion from Pd-Ru membrane. Plots of the rate and constant rate of H2 adsorption/desorption versus temperature in interval 333-573 K were obtained. It was found that H2 sorption is the thermal activated process. The values of amount of H2 adsorbed, rate Ws, constant rate Ks and activation energy of sorption Ea,s of H2 sorption differs for initial foil surface and surface with preadsorbed hydrogen, which inhibits the repeated sorption. Due to preadsorbed hydrogen Ks decreases in 1,5 times (333 K) and Ea,s for molecular form of hydrogen adsorption increases in two times. Kinetics characteristics of hydrogen desorption depend on duration of the expose PdY foil in H2 at room temperature. Long saturation leads to sharply decrease of the hydrogen desorption rate and to some increase of activation energy of desorption varying from 56-68 and 85-108 kJ/mol for first and second kinetic order respectively. Isotherms of hydrogen adsorption were of anomalous shape and can be explained by the induced adsorption model. The results of isotherms analysis agree with kinetic data.