The electrolytic separation factor, α, has been measured for 17O and 18O at Pt and Ni anodes in both light and heavy water solutions of 6MKOH as a function of current density. For oxygen‐17, isotopic separation effects were not observed, within the experimental uncertainty of ±2%, under all conditions studied. For oxygen‐18, three is a small difference of 2% in α values between Pt and Ni in both light and heavy water solutions, but there is no significant difference in α values between light and heavy water solutions. In light water solutions, the separation factor at Pt is small, α(18Ofalse)≤1.02 for i≥0.1 A/cm2 . This value agrees reasonably well with theoretical estimates.
The temperature dependence of the electrolytic hydrogen-deuterium separation factor, SD, was studied on bright platinum bead electrodes as a function of overpotential in 1.2N HCI-10% D20 over the temperature range of 2~176As expected, SD decreased with increasing temperature at a given overpotential. At each temperature, SD increased as the overpotential corrected for /R-drop, *lcorr, increased from 1--25 mV] to about 1--300 mVI; from --300 mV to about --500 mV, the experimental limit, (which corresponds to ~avpl --~ 1.2V) SD remained constant within the ___5% reproducibility of the measurements. This behavior is attributed to a possible change in the mechanism of the hydrogen evolution reaction as In|is increased. The temperature coefficient of SD is independent of nr within the experimental error. The Arrhenius activation energy difference between the hydrogen-deuterium and the hydrogen producing reactions, -~EA, is positive; -~EA decreases as l*lcorrl increases, but reaches a plateau value for ~corr --~1--300 mV]. Conversely, the Arrhenius pre-exponential factor ratio, AH2/AHD, increases over the same range of overpotentials before reaching a plateau value for ~corr ~ 1--300 mV[. Comparison with published work is made.Key words: hydrogen, deuterium, separation factor, isotope separation, effect of temperature on, electrolysis, water, heavy water.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 139.80.123.36 Downloaded on 2015-03-15 to IP [C.A. 57: l1901a]. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 139.80.123.36 Downloaded on 2015-03-15 to IP
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...
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