The Effect of Overpotential on the Electrolytic Hydrogen-Deuterium Separation Factor on Bright Platinum Electrodes in 1.2N HCl-10% D[sub 2]O

Abstract

The electrolytic hydrogen-deuterium separation factor, SD, was studied on bright platinum as a function of overpotential in 1.2N HCI-10% D20 at 25~SD increased from 4.1 • 0.21 at --50 mv to 6.5 • 0.35 at --400 my, and remained virtually constant between --400 mv and --l.2v applied overpotential. Results agree with published work with H2SO4 but not HCI as electrolyte.Only because there is a plateau in the SD vs. overpotential curve are the ohmic potential drop corrections of little significance. The high degree of reproducibility in results achieved, namely • is believed to be due to (a) effective exclusion of Cl2 (anode gas) from the cathode compartment, (b) relatively short (1-60 rain) electrolyses, and (c) removal of the large pre-electrolysis cathode from the cell prior to an electrolysis. A leachingdistillation process was also employed as the pretreatment, and is shown to be as effective as pre-electrolysis. Tafel plots obtained before and after electrolysis showed no hysteresis, and are in agreement with recent work on copper cathodes, where cathodic saturation currents are observed.Many investigators (1-7) have studied the effect of cathode materials, current density, temperature, and the nature and concentration of the electrolyte on the electrolytic hydrogen-deuterium separation factor, SD, 1 usually in an attempt to distinguish between different mechanisms of the hydrogen evolution reaction. More recently, several workers (8-12) have studied the separation factor as a function of the applied electrode potential.To date, very little agreement exists between results of various workers. Thus, for example, the deuterium separation factor for platinum in acid solution has been reported as low as 2 (14) and as high as 9 (11) by different workers. Moreover, even investigators from the same laboratory have obtained different results on the same cathode-electrolyte system (12, 15). Theoretical predictions as to the magnitude of the separation factor are at present conflicting, because of the complexity of the calculations and their inherent assumptions, as Salomon and Conway (16) have pointed out.The present work was u n d e r t a k e n in an attempt to obtain more consistent experimental data. Potentiostatic rather than galvanostatic control was chosen for the work reported here, because it has been shown (17, 18) that the potential at a solid metal electrode can vary with time u n d e r constant current conditions. It will be shown that we have achieved some measure of success in our aim, and that the dependence of the separation factor on overpotential is not greatly altered when the applied overpotential has been corrected for ohmic potential drop in the electrolyte. ExperimentalThe cell.--The separation factor measurements were made u n d e r potentiostatic conditions in a three-compartment cell, (see Fig. 1 and 2) whose temperature was controlled to 0.1~ by a circulating water bath. Each compartment could be isolated by solutionwetted stopcocks. The reference electrode was connected to the cathode compartm...

Electrolytic IVER-MS Technology for the Isotopic Quantitation of Select Electroactive Materials

“…Deuterium isotope.-Historically, the electrolytic hydrogen isotope effect 17 was applied in Norway to manufacture heavy water. More recently, the first of two voltammetric reduction peaks for aqueous formic acid was proposed to involve dihydrogen formation from protonated water.…”