The absorption and diffusion of D into, and through, a Pd membrane electrode in 0.1M LiOD solution were studied by using alternating current impedance and electrochemical permeation cell methods. The alternating current impedance of the electrode was measured for overpotentials which ranged from -0.07 to 0.23V (with respect to a reversible H electrode), that were applied to the cathodic side of the Pd membrane when the D permeation current had reached a steady state. The measured impedance spectra were analyzed by using a complex non-linear least-squares fitting method which was based upon an admittance equation that had previously been derived for treating diffusion-controlled indirect H absorption into a membrane via an adsorbed phase. By assuming the 3-dimensional adsorption of D in the interfacial region, the steady-state current and D coverage were calculated as a function of the overpotential by using the kinetic rate-constants of Volmer adsorption, D absorption reaction and D diffusivity in Pd which best fitted the impedance spectra. The value of the forward rate constant of Volmer adsorption, and the ratio of bulk concentration of absorbed D to surface concentration of adsorbed D, were deduced to be equal to 2.16 x 10-9mol/cm2s and 488/cm, respectively. These values were found to be smaller, by an order of magnitude, than those for H (1.26 x 10-8mol/cm2s and 2350/cm). On the other hand, the value of the backward rate constant was 1.74 x 10-9mol/cm2s. This value was similar to that for H (3.85 x 10-9mol/cm2s). The diffusivity of D in Pd was found to be equal to 5.10 x 10-7cm2/s. This was slightly higher than that for H (3.49 x 10-7cm2/s); thus revealing a reverse isotope effect.

An Investigation of the Electrochemical Kinetics of Deuterium Insertion into a Pd Membrane Electrode in 0.1M LiOD Solution by the AC Impedance Technique. S.I.Pyun, C.Lim, K.B.Kim: Journal of Alloys and Compounds, 1994, 203, 149-56