Measurements of diffusion coefficients of hydrogen in palladium by a galvanostatic permeation method

A study by the galvanostatic permeation technique is reported which has derived reliable and reproducible measurements of diffusion coefficients for hydrogen in palladium. A description is given of the thermostated electrochemical permeation cell. Hydrogen permeation rates have been determined on the detection side of a palladium membrane electrode (geometrical surface area 7.2 cm2; thickness 5 × 10−3 cm) by measuring the anodic current Ia under potentiostatic conditions. Measurements have been made of rising and decaying Ia when the hydrogen entrance side of the membrane has been subjected to constant cathodic currents Ic which were subsequently interrupted after establishments of steady-state conditions. Semi-log plots of Ia against time have yielded reliable determinations of the hydrogen and deuterium diffusion coefficients DH and DD. Studies have been made of the influence on measurement of DH by alterations of Ic, surface roughness of the membrane, variations of electrolyte solution, surface contamination and temperature. Over the temperature range 5–50°C equations representing the temperature dependence of the diffusion coefficients have been determined to be: DH=2.48×10−3exp−5210RT;andDD=1.67×10−3exp−4830RT