The adsorption and diffusion of electrolytic hydrogen in palladium

Abstract

A sensitive electrochemical technique, which permits the recording of the instantaneous rate of permeation of electrolytic hydrogen through palladium, is described. Results were obtained under conditions required by theory for the diffusion of hydrogen with the use of electronic potentiostats. Analysis of the results shows the validity of the equations previously deduced for the diffusion of hydrogen. No anomalies in the diffusion have been found under these conditions. Thus the diffusion constant is found to be independent of thickness in the range 0.0035 to 0.054 cm. The permeation has been found to be inversely proportional to thickness as required by theory. The diffusion constant for a hydrogen poor $\alpha$-palladium has been found to be 1.30 $\pm$ 0.20 x 10$^{-7}$ cm$^2$ s$^{-1}$ at room temperature. Reasons for permeation anomalies reported in the literature for diffusion of hydrogen from the gas phase are discussed. Attention is drawn to errors in the classical time lag determination which unless corrected, can give rise to spurious thickness and temperature dependence of the diffusion constant.