Electrolytic Separation Factor Research Articles

The determination of the protium-deuterium electrolytic separation factor by infrared-cryogenic gas chromatography method

A method IR-CGC (infrared-cryogenic gas chromatography) was established directly through the combination of infrared spectrum (IR) and cryogenic gas chromatography (CGC) to measure the electrolytic separation factor (α) between protium and deuterium. The n1,liq(D)/n2,liq(H) ratio of alkalic aqueous solution after electrolysis was tested quantitatively by the IR method, and the n1,gas(D)/n2,gas(H) ratio of mixed gases from electrolysis was determined by CGC. Then α of different electrode materials were obtained according to the formula of electrolytic separation factor. As a result, it provides an accurate, simple, feasible, suitable approach for evaluating the electrolytic protium-deuterium separation ability of different electrode materials, which is helpful for searching excellent hydrogen isotopes separation materials.

Electrochemical and Isotopic Investigation of 13C-Enriched Oxalic Acid Facilitated with a Vacuum Electrochemical Reactor

The electrolytic decomposition of 13C-enriched oxalic acid was investigated. Oxalic acid and oxalic acid-13C2 were pre-purified by vacuum sublimation and characterized by assay, melting range, and FTIR. An Integrated Vacuum Electrochemical Reactor (IVER) was employed to convert aqueous-phase oxalic acid to CO2 for the 13C-enrichment determinations: oxalic acid solvation, vacuum degas, electrolysis, and mass spectrometric analysis. Highly enriched oxalic acid-13C2 was electrolyzed at 1.5-VDC and the CO2 determined to be 99.5 atom%-13C. Blends of H2C2O4 and H213C2O4 were prepared from 50.5 to 99.5 atom%-13C, dissolved in water, and electrolyzed. For each blend solution, the [12C/13C] isotope separative effect was observed as increases in the (CO2) 13C-enrichment when the aqueous-phase was repeatedly electrolyzed. Furthermore, 50 atom%-13C oxalic acid was electrolyzed while the IVER current was monitored, and thereby the electrolytic isotope separation factor α[12C/13C] is estimated to be 1.03 ± 0.01, at 295 K on platinum. Cyclic voltammograms of 0.10-mole% oxalic acid in water displayed an irreversible oxidation peak at E = +0.95 volt (oxalic acid) and another oxidation peak at E ≥+1.6 volt (water). Cyclic voltammograms of oxalic acid in EMI+BETI− indicate that H2C2O4 can also be oxidized in liquid salts (voltammetric window ∼ 1.4 volt versus Ag/AgCl).

Electrolytic Enrichment of Tritium with Solid Polymer Electrolyte for Application to Environmental Measurements

We evaluated electrolytic separation factors of hydrogen isotopes by SPE (Solid Polymer Electrolyte) for application to environmental tritium analysis. The apparent separation factors αa for deuterium and βa for tritium were determined as 3.5 ± 0.1 and 6.2 ± 0.5, respectively. The tritium enrichment of 8.4 times was achieved, when a 1000 ml of sample water was electrolyzed to about 60 ml. The chemical composition changes before and after the electrolysis were examined, showing an increase in H+ and Na+ concentrations and a decrease in Mg2+ and Ca2+concentrations. F-, which was not contained in the sample water, was detected after electrolysis accompanying with a reduction of SO42-, Cl- and NO3-. The memory of tritium and ions in the electrolysis cell after electrolysis was possible to be eliminated by washings with de-ionized water. Tritium concentrations of rain at Kumamoto, Japan were determined with a combination of the present electrolytic enrichment system and liquid scintillation counting.

Improved deuterium separation factor for the iron electrode prepared in a magnetic field

The electrolytic deuterium separation factors were measured in KOH aqueous solution at 298 K for the two iron films electrodeposited in no magnetic field (film (a)) and a magnetic field of 0.5 T (film (b)). The separation factors were higher for film (b) (9.8–12.3) than those for film (a) (8.7–10.2). From the exchange current density and the real surface area, it was found that film (b) has higher electrocatalytic activity for the hydrogen evolution reaction. The SEM images showed cracks on the whole surface for film (b), which suggests that the strain energy is stored. The improved electrocatalytic activity for the HER is explained by the preferred adsorption of proton due to the strain energy in the film. The increase of the deuterium separation factor is also explained by the electrocatalysis activated by the strain energy.

Electrolytic Separation Factor for Hydrogen and Deuterium on Platinum Electrode

The electrolytic separation factor (S factor) of hydrogen isotopes for platinum was measured by means of quantitative mass analysis. The S factor was 5.0±0.2 at 298 K in sulfuric solution. The value was discussed on the basis of the transition state method. The temperature effect on the S factor was observed and the activation energy difference of 7.2 kJ/mol (Δe=e D -e H ) was obtained. The origin of Δe was discussed, and it was revealed that the hydrogen evolution process on Pt is assigned to a slow recombination mechanism. The present S factor measurements were done in the overvoltage region. In this region, it was recognized that the S factor is independent of the electrode current density. The S factor in the undervoltage region was discussed by taking account of electrochemical studies reported previously.

Electrolytic enrichment of tritium with Fe-Ni and Ni-Ni electrodes and estimation of tritium enrichment factor using Fe-Ni electrodes.

The electrolytic separation factors of tritium, (T/H)water/(T/H)hydrogen, and the relationship between the tritium enrichment factor, Tf/Ti, and the final volume of water have been evaluated for Fe-Ni and Ni-Ni electrodes. The tritium separation factor for the Fe-Ni electrodes (25.9 ± 3.4) is systematically higher than that with the Ni-Ni electrodes (14.4 ± 4.4) when the electrolysis is conducted under similar conditions. The tritium separation factor with the Fe-Ni electrodes obtained in this study is similar to that obtained in previous studies. Chemically impure mild steel used in this study as a cathode material gives a high tritium separation factor as well as pure iron employed in previous studies. The tritium enrichment factor with the Ni-Ni electrodes shows a wide variation at a given final volume, depending upon the tritium separation factor. On the contrary, the tritium enrichment factor obtained with the Fe-Ni electrodes changes as a function of the final volume. When tritium in the sample is enriched 20–25 times with the Fe-Ni electrodes, a reliable tritium enrichment factor can be obtained directly from the final volume with an accuracy of ±3.5% (2σ) without measuring the deuterium or simultaneous electrolysis of a tritiated reference water.

Electrolytic Separation Factors for Oxygen Isotopes in Light and Heavy Water Solutions

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 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, for . This value agrees reasonably well with theoretical estimates.

The establishment of equilibria in the Pd-H 2-D 2-H 2O-D 2O system

Palladium can absorb large volumes of the isotopes of hydrogen. Analysis of the ratios of isotopes in outgassed mixtures provides a means of determining electrolytic isotopic separation factors and also of determining ratios of isotopes absorbed within electrodes after equilibria have been established with respect to the hydrogen and deuterium dissolved in surrounding mixtures of H 2O and D 2O. Measurements were made at values of hydrogen (deuterium) contents corresponding to the α, α-β and β phase composition ranges in the Pd-H(D) system.

Measurement of heavy water concentration with a density meter

A densitometric technique involving the use of a high-sensitivity density meter is described for the determination of a wide range of deuterium contrations in water. The effects of temperature and solute impurities on the method were determined and the purification of water by sublimation and anion-exchange techniques were examined as a means of overcoming the latter. Standard heavy water samples of various concentrations were analysed by this densitometric method and by mass spectrometry, and good agreement between the results was found. The application of the proposed method to the determination of the electrolytic separation factor, α, for deuterium-hydrogen is described.

Change of mechanism of the hydrogen electrode reaction with overpotential—III. Potential dependence of the deuterium separation factor on Pt, Au and Ni cathodes

A relationship between the overall electrolytic deuterium separation factor of the hydrogen electrode reaction and the separation factors of the steps that constitute the reaction is formulated for the discharge-combination route, without assuming an overwhelming unique rate-determining step. This is utilized for the quantitative interpretation of sharp variation of the cathodic deuterium separation factor with overpotential observed on Pt and Au in aqueous H 2SO 4 and an insignificant variation on Ni in alkaline solutions. The variation on Pt and Au is interpreted in terms of change with cathodic overpotential of the mechanism from the rapid discharge—slow combination to the slow-discharge. The variation on Ni is expected to be significant only in the anodic region.

Separation Factor of Hydrogen and Deuterium by Suspension Electrolysis Using Mercury Cathode

The electrolytic separation factor between hydrogen and deuterium was examined using mercury or else platinum cathode immersed in IF NH4Cl in 10v/oD2O water containing cobalt sulfide powder in suspension. Several other kinds of powdered materials in suspension were also studied. In the case of mercury pool electrode, the materials added in suspension were effective in enhancing the hydrogen/deuterium separation factor, but powder suspension was ineffective on platinum plate electrode. The powdered material added in suspension served as catalyst on the hydrogen evolution reaction at the mercury cathode. The influence of the applied potential on the separation factor was studied over the temperature range of 15°~80°C. The results provided an indication of the rate-determining steps governing the electrolytic hydrogen evolution. The experimental values obtained for the separation factor and activation energy gave an insight into the mechanism of the rate-determining step of the hydrogen evolution at the working electrode.

Electrolytic H/D separation factors on cathode and diffusion sides of iron membranes in H2SO4

The electrolytic hydrogen-deuterium separation factor has been measured, simultaneously for the first time, on both the cathode and the diffusion side of thin iron membranes in acid solution at room temperature as functions of time and current density. Both separation factors decreased with time and reached plateau values of 7.35±0.5 and 10.7±0.4, respectively; neither is a simple function of current density. Possible explanations for these observations are given. The separation factor on the diffusion side is always larger than that on the cathode side, the average ratio being 1.35–1.6 over the current density range 19.1–255 mA cm −2 . An estimate of the permeation rate of hydrogen was obtained and the variations in this quantity are accounted for in terms of the screened proton model.

Electrolytic H/D separation factors on cathode and diffusion sides of iron membranes in H 2SO 4

Summary The electrolytic hydrogen-deuterium separation factor has been measured, simultaneously for the first time, on both the cathode and the diffusion side of thin iron membranes in acid solution at room temperature as functions of time and current density. Both separation factors decreased with time and reached plateau values of 7.35±0.5 and 10.7±0.4, respectively; neither is a simple function of current density. Possible explanations for these observations are given. The separation factor on the diffusion side is always larger than that on the cathode side, the average ratio being 1.35–1.6 over the current density range 19.1–255 mA cm−2. An estimate of the permeation rate of hydrogen was obtained and the variations in this quantity are accounted for in terms of the screened proton model.

A system for accurate and fast measurement of the gas phase H/D ratio in electrolytic H/D separation factor experiments

Accurate and fast measurements of electrolytic hydrogen-deuterium separation factors are required to study short-term time effects and the effects of other variables, for example overpotential, before the cathode has suffered irreversible changes such as hydrogen embrittlement. A system for fast measurement of the hydrogen-deuterium ratio of the liberated hydrogen isotopes in argon as the sweep gas has been developed and is described in detail. Unique features include a modified Cartesian manostat and an automatic Toepler pump in the gas collection system, and an automatic mass spectrometer inlet system whose cycle time is about 4 min. Calibration procedures are outlined. The accuracy and reproducibility in the H/D ratio are ±1% and ±0.5% respectively, for the range 0.75 to 5.0 mol. % deuterium in mixtures containing 0 to 80 vol.% argon.

Electrolytic separation factors on palladium

Summary It is shown that the separation factor for the slow discharge step of hydrogen onto palladium is ∼13 and that this corresponds to an essentially unbound transition state. The separation factor for the overall hydrogen evolution reaction, due to a fast electrochemical desorption step, is close to the equilibrium value, 4. This assignment of mechanism agrees with that deduced from the iinetic data. The separation factor for diffusion through palladium membranes is 10.5. In addition, it is possible to measure the separation factor for the fully formed β phase and this approaches 9.5 at negative potentials which corresponds to that calculated for free protons in the lattice. The variation of this separation factor with potential cannot be adequately explained in terms of simple models of localised oscillators.

Electrolytic separation factors on palladium

Electrolytic separation factors on palladium

Electrolytic separation factors on platinum under non-steady state conditions

Electrolytic separation factors on platinum under non-steady state conditions

Electrolytic separation factors on platinum under non-steady state conditions

Summary A new method for studying the non-steady state separation factor of hydrogen and deuterium on platinum has been developed with a view to investigating the fast step in the hydrogen evolution reaction. It has been shown that the measurement of the separation factor on platinum as a function of frequency can be interpreted only in terms of a progressive weakening of the platinum-hydrogen bond with increasing coverage. The discharge of H + on D must also be much faster than that of D + on H.

The electrolytic H/D separation factor-agreement of the experiment with the hypothetical maximum value

A fresh approach to separation factor studies is described based on ( a ) a search for conditions giving maximum experimental values of S (optimisation), ( b ) the use of an isotopic ratio (H:D=20:80) which simplifies theoretical interpretation and minimises experimental error. Two methods are developed for obtaining H/D electrolytic separation factors under clearly defined experimental conditions. The first consists in continuously maintaining a fresh cathode surface by depositing cathode material onto it while hydrogen evolution is in progress (the scavenging technique). The second consists in displacing other surface impurities by the deliberate use of bath additives which adsorb onto the cathode so that the surface is maintained in a definite, reproducible state (the displacement technique). When both methods are combined in hot alkaline electrolytic baths having iron electrodes, certain of the additives investigated (EDTA and urea) thereafter give maximal, reproducible experimental separation factors Such baths are said to be optimised and optimisation persists even when the baths are subsequently operated at low temperatures. The optimised results so obtained are of considerable theoretical interest since o 1. The position of their Arrhenius plot is shown to identify the rate-step unequivocally as a slow discharge. 2. The slope of this plot is indistinguishable from that for the hypothetical maximum separation factor S max . This identity of both position and slope is the first example to be found of clearcut agreement between experiment and theory for Arrhenius plots of electrolytic separation factors. However it presents difficulties of interpretation since the theoretical maximum value requires a transition-state consisting of free, gaseous, atomic hydrogen—a condition unlikely to exist at the cathode. Suggested models to account for: ( a ) this identity of experimental and hypothetical values and ( b ) the mechanism of optimisation, are discussed. In addition to its theoretical significance, the discovery of the optimising effect of certain impurities may account for lack of reproducibility in previously reported values of S .

The electrolytic H/D separation factor-agreement of the experiment with the hypothetical maximum value

A fresh approach to separation factor studies is described based on (a) a search for conditions giving maximum experimental values of S (optimisation), (b) the use of an isotopic ratio (H:D=20:80) which simplifies theoretical interpretation and minimises experimental error. Two methods are developed for obtaining H/D electrolytic separation factors under clearly defined experimental conditions. The first consists in continuously maintaining a fresh cathode surface by depositing cathode material onto it while hydrogen evolution is in progress (the scavenging technique). The second consists in displacing other surface impurities by the deliberate use of bath additives which adsorb onto the cathode so that the surface is maintained in a definite, reproducible state (the displacement technique). When both methods are combined in hot alkaline electrolytic baths having iron electrodes, certain of the additives investigated (EDTA and urea) thereafter give maximal, reproducible experimental separation factors Such baths are said to be optimised and optimisation persists even when the baths are subsequently operated at low temperatures. The optimised results so obtained are of considerable theoretical interest sinceo1.The position of their Arrhenius plot is shown to identify the rate-step unequivocally as a slow discharge.2.The slope of this plot is indistinguishable from that for the hypothetical maximum separation factor Smax. The position of their Arrhenius plot is shown to identify the rate-step unequivocally as a slow discharge. The slope of this plot is indistinguishable from that for the hypothetical maximum separation factor Smax. This identity of both position and slope is the first example to be found of clearcut agreement between experiment and theory for Arrhenius plots of electrolytic separation factors. However it presents difficulties of interpretation since the theoretical maximum value requires a transition-state consisting of free, gaseous, atomic hydrogen—a condition unlikely to exist at the cathode. Suggested models to account for: (a) this identity of experimental and hypothetical values and (b) the mechanism of optimisation, are discussed. In addition to its theoretical significance, the discovery of the optimising effect of certain impurities may account for lack of reproducibility in previously reported values of S.