Diffusion and permeation of hydrogen/deuterium in palladium electrode

Electrochemical properties of palladium electrode in electrolytes of light/heavy waters, permeation efficiency and diffusion behaviors of hydrogen/deuterium through palladium were investigated. From potential change of Pd electrode during hydrogen/deuterium charging and polarization curves after charging, growth rate of β-phase is higher in heavy water than that in light water. The rate of hydrogen/deuterium absorption into palladium in acidic solution is higher than in alkaline solution. By using AC modulation technique diffusion coefficients of hydrogen DH and deuterium DD were evaluated as a function of temperature and charging time. At lower charging current, DH increases with charging time, probably due to filling trap states in Pd. On the other hand, at higher charging current, DH decreases with charging time. This result can be explained by formation of a new phase with high H/Pd ratio at Pd surface in which DH is smaller than that in the known phase (α or β-phase). (author)