The effects of the electrical parameters, surface roughness, surface contamination, and electrolyte concentration (NaOH or H2SO4) upon the permeation rate of H through a Pd membrane (0.05mm) were reported. Diffusion measurements were carried out by using an electrochemical permeation cell under transient conditions. The cathodic side of the membrane was subjected to a constant H concentration or H flux, while the anodic side was kept permanently at a negligibly low H concentration. The diffusion coefficient was calculated from the charging or stripping current, expressed as a function of time. Reproducible values of the diffusion coefficient were deduced from both charging and stripping curves under galvanostatic charging conditions. Reliable values were obtained only from stripping curves under potentiostatic charging conditions. It was found that the diffusion of H and D, at temperatures ranging from 5 to 50C, could be described by the expressions:

H:     D (cm2/s) = 0.00248 exp[-5.21(kcal/mol)/RT]

D:     D (cm2/s) = 0.00167 exp[-4.83(kcal/mol)/RT]

The diffusivities of H and D at 298K were equal to 3.8 x 10-7 and 4.8 x 10-7cm2/s, respectively. These values agreed well with those obtained by using non-electrolytic methods.

R.V.Bucur: Zeitschrift für Physikalische Chemie, 1985, 146[2], 217-29