IN-SITU COMPARISON OF DIFFUSIVITIES FOR HYDROGEN AND DEUTERIUM IN PALLADIUM

An electrochemical permeation method was employed to study the diffusi on behaviour of hydrogen and deuterium in palladium. Solutions of 0.1 M LiOD (in D2O) and 0.1 M LiOH (in H2O) and their mixtures were used a s the catholytes. More than one hundred diffusivity data from 20 palla dium membranes were collected. Statistical analysis of these data was made to examine the validity of the reversed isotope dependence for hy drogen diffusion in palladium. It was concluded that the effective dif fusivities increased with the concentration of deuterium in the electr olyte. In addition, an in situ experiment was also performed by adding to the cathodic cell an equivalent amount of LiOD solution to the ori ginal LiOH solution, or vice versa. Graphical comparison of the corres ponding permeation transients showed that the permeation rate increase d when deuterium was added to the solution of H2O, and the rate decrea sed when hydrogen was added to the solution of D2O. This constitutes d irect evidence for the higher diffusivity of deuterium than that of hy drogen in palladium.