Decomposition Voltages Research Articles

Clean preparation of V2O3 by one-step molten salt electrochemical reduction of soluble NaVO3

Vanadium oxides, such as V2O5 and V2O3, are important metallurgy products and mainly used to prepare V-based alloys for steelmaking. At present, vanadium oxides are mainly produced by complex sodium salt roasting process. Serious environmental pollution, such as emission of ammonia nitrogen wastewater and NH3, are restrictive problems. Here, a clean and sustainable method for V2O3 preparation is proposed by one-step molten salt electrochemical reduction of soluble NaVO3, i.e. an indispensable intermediate in traditional V metallurgy. The pollution issues are well solved. The theoretical decomposition voltages of different vanadate to various low-valence vanadium oxides were calculated. NaVO3 with a solubility of 14.7 wt% is the most suitable vanadate for the direct preparation of V2O3 by molten salt electrolysis. The effects of cathode structure, NaVO3 content, electrolysis temperature and voltage on current efficiency and electricity consumption were systematically studied. High-purity V2O3 with uniform particle distribution is obtained and the lowest electricity consumption is only 2.86 kWhkg−1. V2O3 is mainly produced by one-step electrochemical reduction of soluble NaVO3 through two-electron transfer process. The economic evaluation for ferrovanadium production is preliminarily carried out. Compared with the traditional process, the cost for ferrovanadium production is lower by the aluminothermic reduction of V2O3 which is prepared by clean one-step electrolysis of soluble NaVO3.

Impurity Behavior in Aluminum Extraction by Low-Temperature Molten Salt Electrolysis

Alumina-containing waste can potentially be used to produce a coarse Al–Si alloy by carbothermal reduction and subsequent aluminum metal extraction by soluble anode electrolysis. However, metal impurities in the alloy have important effects on the product purity. In this study, anodic dissolution of the coarse Al–Si alloy and cathodic electrochemical reduction of metal impurity ions in the electrolyte were investigated. The phases, element distributions, and compositions of the anode, electrolyte, and products were investigated by X-ray diffraction, scanning electron microscopy, and inductively coupled plasma atomic emission spectrometry. When using an aluminum wire of diameter 2 mm as reference electrode, the order of anodic metal dissolution is Mg > Ca > Al > Fe > Si > Ti > Mn, and that of metal impurity ion reduction in the electrolyte is Fe > Si > Al > Mg > Ca. Mg and Ca dissolve into the electrolyte before aluminum does, but they have little effect on the product purity because of their high decomposition voltages. Fe and Si in the alloy anode begin to dissolve at electrode potentials of 0.4 and 0.7 V, respectively. If keeping the electrode potential lower than 0.3 V, the Al purity reaches 99.9%.

Physical and Electrolytic Properties of Partially Fluorinated Organic Solvents and Its Application to Secondary Lithium Batteries: Partially Fluorinated Dialkoxyethanes

This paper investigated the physical and electrolytic properties, and charge-discharge characteristics for secondary lithium batteries of partially fluorinated 1-ethoxy-2-methoxyethane (EME) and 1,2-diethoxyethane (DEE) derivatives newly synthesized by us. Dielectric constants of fluorinated EME and DEE derivatives are almost independent of the number of fluorine atom. Viscosities of the fluorinated derivatives with three fluorine atoms are not affected by the molecular weights of them. Donor numbers of the fluorinated derivatives were estimated by 29Si NMR chemical shifts of triphenylsilanol. Conductivities of the fluorinated derivatives are dependent on the donor numbers of them. Oxidative decomposition voltages tend to increase with increasing the number of fluorine atom. EC-based equimolar binary derivative solutions with three fluorine atoms show higher lithium electrode cycling efficiencies. In general, EC-based fluorinated EME and DEE derivative solutions show higher discharge capacities and cycling efficiencies for Li | LiCoO2 cells.

Electrochemical Window of a LiCl-KCl-CsCl Melt

The electrochemical window of the LiCl-KCl-CsCl melt (57.5:13.3:29.2 mol %, m.p.; 538 K) was investigated at 573-723 K. The cathodic limit of this melt for a nickel electrode was confirmed as lithium deposition from the results of differential scanning calorimetry and inductively coupled plasma atomic emission spectroscopy. Conceming the anodic limit of this melt, chlorine was confirmed to be evolved on a glassy carbon electrode from the result of the gas analysis. The electrochemical windows were determined as 3.75 and 3.62 V at 573 and 723 K, respectively. These values agreed well with theoretical decomposition voltages of LiCl.

The effect of ultrasonic frequency and intensity upon electrode kinetic parameters for the Ag(S2O3)23−/Ag redox couple

This paper describes the effect of ultrasound on electrochemical parameters important in the removal of silver from photographic processing solutions. Decomposition voltages (obtained galvanostatically) and discharge potentials (obtained potentiostatically) for the reduction of the silver complex, Ag(S2O3) 2 3- was studied in dilute aqueous Na2S2O3/NaHSO3 solution on stainless steel and carbon disc electrodes in both the absence and presence of ultrasound. Under silent conditions, silver deposition is the main reaction occurring at the electrode. Under sonication at 20 kHz and 500 kHz, the reduction wave shifts anodically with increasing ultrasonic intensity. Similarly, the discharge of hydrogen and oxygen shifts anodically and cathodically respectively with increasing ultrasonic power. The decrease in decomposition voltage in the presence of ultrasound is due to the combined effect of a decrease in anodic overpotential and an increase in cathodic overpotential.

New lithium-ion conducting compounds 3Li 3N-MI (M = Li, Na, K, Rb) and their application to solid-state lithium-ion cells

In the quasi-binary systems Li 3N-MI (M = Li, Na, K, Rb) new intermediate compounds 3Li 3N-MI were synthesized by a solid-state reaction between Li 3N and MI at 600°C. They were isomorphous and had a tetragonal unit cell. Their sintered bodies exhibited lithium-ion conductivity of 1.1 × 10 −4–7.0 × 10 −5 S cm −1 at room temperature. The grain boundary resistances were negligibly small because of their good sinterability. The decomposition voltages were approximately 2.5–2.8 V, much higher than that of Li 3N. Even the compacts of the powdered compounds showed total conductivities more than 10 −5 S cm −1. This allowed the cell construction of the solid-state lithium-ion cell, C/3Li 3N-KI/LiTiS 2, simply by pressing the powdered electrolyte and electrode materials. The cell was able to charge and to discharge at a constant current of 15 μA cm −2 at room temperature; however, severe polarization in the positive electrodes limited the charge/discharge performance.

Vitreous State Electrolysis of F− Ion Conducting ZrF4 ‐ BaF2 ‐ CsF and FeF3 ‐ MnF2 ‐ PbF2 Glasses

Fluoride ion conducting and glasses were found to permit electrolysis in vitreous states. The decomposition voltages of the and glasses were about 4.1 and 2.2V, respectively. The electrode reactions in the glasses proved to be at the anode and at the cathode, whereas the electrode reactions in the glasses were at the anode and at the cathode. In both types of glasses, the oxidation reaction at the anode released fluorine gases from the glass surface just below the anode electrode, causing volume contraction of the glasses. In the glasses the reduction reaction at the cathode produced a black film just below the cathode electrode. In the glasses, the reduction reaction proceeded homogeneously throughout the glass matrices across which a potential existed because these glasses acted as mixed fluoride ion and electron conductors.

A NEW HYBRID THERMOCHEMICAL CYCLE FOR PRODUCTION OF HYDROGEN FROM WATER

A new hybrid cycle to produce hydrogen from water, which consists of a thermochemical reaction (3) and an electrochemical reaction (4), has been devised.2KNO 3 +I 2 →2KI+2NO+2O 2 , (3)2NO+3/2 O 2 +2KI+H 2 O→2KNO 3 +I 2 +H 2 . (4)The change in free energy of the reaction (3) decreases as temperature rises. and the temperature, at which the △G° is zero, is about 950 K. The electrochemical reaction (4) could be divided intoanode 2I - →I 2 +2e - (7)andcathode 2H + +2e - →H 2 (8)in electrolysis cell with an ion-exchange resin. So, the standard equilibrium decomposition voltage of the reaction (4) is 0.54 V.The preliminary experimental investigations were carried out. The yields of the reaction (3) increase as the temperature rises, and KNO 3 is converted into KI casily and rapidly, when reacting with gaseous iodine above 1000 K. The polarizations of the electrolysis reaction were small. The sum of the equilibrium decomposition voltages and overvoltages—0.56, 0.65 and 0.78 V at 100, 500 and 1000 mA·cm -2 , respectively, was obtained.

The electrochemical properties and stability of polyacetylene in organic electrolyte solutions

This paper describes the electrochemical properties and stability of (CH) x in a cell containing organic electrolyte solutions. Cis- and trans-( CH) x can be partly oxidized(p-doped) and reduced(n-doped) electrochemically. When the cell containing the neutral (CH) x ( i.e., without doping) is charged or discharged, its electrode potential immediately increases or decreases. The oxidation or reduction of (CH) x does not occur at that instant, but a space charge region in the semiconductor (CH) x film forms. After that, its electrode potential slowly changes with the doping processes. The amount of change in the electrode potential of CH) x during the processes of oxidation or reduction depends mainly on the energy band-gap E g of (CH) x . The factors affecting the stability of the doped (CH) x are very complicated. According to our experiments, the decomposition voltages of solutions and the properties of solvents and salts play an important part in the stability of doped (CH) x .

Electrolytic Behavior of Mixed Network-Forming Oxides Glass Melts

The electrolytic behavior of molten glass is important to understand its ionic behavior and is also essential to control an electric melting furnace. The present investigation was undertaken to obtain the fundamental electrolytic behavior of various glass melts composed of mined network-forming oxides such as borosilicate, phosphoaluminate, boroaluminate, phosphoborate and aluminosilicate. Besides the potential sweep voltammetry, decomposition voltages were determined from stationary current-potential curves. The elemental compositions of the Pt electrode-glass interface after polarization were analyzed by EPMA. Decomposition voltages at 900°C were determined as follows; 25Na2O⋅25B2O3⋅50SiO2: 1.46V, 40Na2O⋅20Al2O3⋅40P2O5: 1.05V, 40Na2O⋅30Al2O3⋅30B2O3: 1.19V, 40Na2O⋅30B2O3⋅30P2O5: 1.02V, The value in 26Na2O⋅19CaO⋅8Al2O3⋅47SiO2 was 0.96V at 1200°C. The network-forming or conditional ions were reduced at different potentials and the order subject to reduction was confirmed to be (easy) P5+>Al3+>Si4+>B3+ (difficult). The decomposition potentials of these ions were tentatively estimated to be P5+: -0.7V, Al3+: -0.85V, Si4+: -1.1V, B3+: -1.2--1.4V with respect to the electrode potential of the Pt reference immersed in the respective molten sample glass. On the Pt anode, oxygen anions were oxidized resulting in oxygen gas evolution.

Thin film solid state polymer electrolytes containing silver, copper and zinc ions as charge carriers

The ionic conductivities, decomposition voltages and limiting discharge potentials were measured in a series of poly(ethylene-oxide)-complex salts of silver, copper and zinc. The ionic conductivities range from 1×10 −5 (Ω cm) −1 for (PEO) 4AgClO 4 to 1.2×10 −9 (Ω cm) −1 for (PEO) 8CuCl 2 at room temperature and the stability window widths range from 1.3V for (PEO) xAgClO 4 to 3.3V for (PEO) 4.KI.2ZnCl 2.

Electrolysis of ammonium iodide solution in a Na 2CO 3I 2 hybrid cycle

The electrolysis step in the following hybrid cycle Na 2CO 3+I 2→2NaI+CO 2 1 2 O 2 2NaI+2NH 3+2CO 2+2H 2O→2NaHCO 3 +2NH 4I 2NaHCO 3→Na 2CO 3+CO 2+H 2O ▪ was studied. The solubility of iodine in the anolyte (NH 4I-I 2 solution), steady state compositions of the catholyte (NH 4I-NH 3 solution), polarization characteristics for both electrolyte solutions and the nature of ion-exchange membranes was examined. The polarizations of the anode were very small, in a range up to 1000 mA cm −2, and those of the cathode were also relatively small. An advantageous feature of this electrolysis over NaI electrolysis [1] is that a large current density is obtainable. Decomposition voltages assumed from the polarization curves are small compared with NaI electrolysis. This improvement arises from greater solubilities of electrolytes. Among the ion-exchange membranes tested, Nafion was usable because of durability of the electrolyte solution and low permeation of iodine.

New fast solid lithium ion conductors at low and imtermediate temperatures

Three approaches for practically useful new solid lithium electrolytes are presented. Combination of two binary lithium salts provides materials which are stable against reaction with lithium and decompose at intermediate values of the decomposition voltages of the two binary salts. Results are given for systems based on the ionic conductor Li 2S and lithium halides. A small number of ternary lithium compounds exist which contain a second type of cations with a higher binding energy to the anion than lithium. These materials are also stable with lithiums. Results obtained for the compounds LiMgN and Li 3AlN 2 which crystallize both in an antifluorite type structure are reported. The third class of solid lithium ion conductors are addition compounds formed from lithium halides and alcoholes. LiI.4CH 3OH shows a room temperature conductivity of 2.2×10 −4 Ω −1cm −1 and an activation enthalpy of 0.51 eV.

Decomposition of Hydrogen Bromide or Iodide by Gas Phase Electrolysis

Abstract Gas phase electrolysis of HBr or HI was studied by using a fuel-cell-type electrolyzer provided with graphite gas diffusion electrodes and liquid film electrolyte of H3PO4. Current efficiency 100% may be achieved at decomposition voltages of 0.73 V (at 100 mA cm−2 and 150 °C) for HBr and 0.28 V (at 100 mA cm−2 and 145 °C) for HI. Both bromine and iodine produced may smoothly be evolved out of the anode in the gas or liquid form without being dissolved into the electrolyte H3PO4, causing no trouble on the separation of products. This electrolytic method may be incorporated in the bromine or iodine cycles for thermochemical hydrogen production to constitute an effective hybrid system.

Electrolytic deposition of silicon and of silicon alloys Part III: Deposition of silicon and aluminum using a copper cathode

AbstractThe decomposition voltages of SiO2 and Al2O3 dissolved in cryolite were measured using a copper cathode. In a melt containing 90 wt% Na3AlF6 + 10 wt% Al2O3 at 1030°C the decomposition voltage of alumina was found to be Ed = 1.50 ± 0.05 V. In a melt containing 95 wt% Na3AlF6 + 5 wt% siO2 the value of the decomposition voltage was determined to Ed = 1.10 ± 0.05 V. In Na3AlF6-Al203-SiO2 mixtures the decomposition voltage of silica was found to increase with increasing concentration of alumina in the electrolyte.It was determined that at current densities below 0.2 A·cm−2 only silicon was deposited at the cathode whereas at higher current densities Si and Al were deposited simultaneously. The deposition ratio was found to depend on the current density.The distribution of silicon in the Si-Cu alloy was determined by spectroscopic analysis. It was found to be a function of the current density and of the diffusion rate of the deposited metal in the alloy. Resume Les auteurs mesurent sur cathode de cuivre...

Electrolytic deposition of silicon and of silicon alloys Part II: Decomposition voltages of components and current efficiency in the electrolysis of the Na<SUB>3</SUB>AlF<SUB>6</SUB>-Al<SUB>2</SUB>O<SUB>3</SUB>-SiO<SUB>2</SUB> mixtures

Electrolytic deposition of silicon and of silicon alloys Part II: Decomposition voltages of components and current efficiency in the electrolysis of the Na<SUB>3</SUB>AlF<SUB>6</SUB>-Al<SUB>2</SUB>O<SUB>3</SUB>-SiO<SUB>2</SUB> mixtures

ELECTROLYTIC REDUCTION AND ELLINGHAM DIAGRAMS FOR OXY-ANION SYSTEMS

Standard reversible decomposition voltages, E0, for various decomposition reactions of K2CO3, Na2CO3, Li2CO3, BaCO3, CaCO3, MgCO3, Na2SO4, NaNO3, and KNO3 are calculated from thermal data and the values obtained plotted against temperature. That reaction which has the lowest values of E0 is considered to be the most likely to occur when the particular salt is electrolyzed. The results obtained indicate that in the case of the carbonates metal deposition is possible only for K2CO2 and Na2CO3 above 870 °K. In all other cases metal oxide and carbon (or CO at higher temperatures) are the favored cathode products. For Na2SO4, Na2S and Na2O are the favored cathode products and for the nitrates, nitrite and oxide or nitrogen evolution and oxide formation appear equally feasible thermodynamically.Once the likely electrolytic decomposition products are known, a method is presented whereby the products formed by reduction of the oxy-anions by metals (and in the case of the carbonates, by carbon) may be predicted. This method involves drawing an appropriate redox line on an Ellingham diagram. Finally, a comparison is made between the thermodynamic predictions and the few experimental results available.

Theoretical Electromotive Forces for Cells Containing a Single Solid or Molten Chloride Electrolyte

From thermodynamic data, electromotive forces have been calculated for reversible galvanic cells of the type where M is a metallic element in the solid, liquid, or gaseous state and is the corresponding chloride in the solid or liquid state. Results are given for temperatures from 25° to 1500°C.The chlorides are listed in a series and compared with the electromotive force series of the elements in aqueous solutions. Comparisons are given with results obtained from galvanic cells with fused chlorides or from measurements of decomposition voltages.

溶融スラツグの電氣化學的研究(I)

Up to this time, the potential measurment of molten slags was scarcely performed in comparison with that of the viscosity and electrical conductivity. In this paper, the author measured potentials in the binary systems K2O, Na2O, BaO, CaO-SiO2 making use of the C-SiC electrode couple with the object of determination of activities of the constituents. As the result, it was clear that the systems K2O, Na2O-SiO2; BaO-SiO2; CaO-SiO2 had some characteristics both in the magnitude and polarity of potential. This fact was due to the substantial difference in the construction of these systems.Moreover, the next relations were proved to be established between the activities aSiO2 aCaO of these slags and potentials, where E, E': measured e.m.f., Eo, Eo': standard e.m.f., m, m': molar numbers of constituents, n, n': numbers of electron, R: gas constant, T: absolute temperature, F: Faraday's constant.The author suggested that asio2 or aCaO could be derived from the measurement of the decomposition voltages and this potential values.

Some Observations on Decomposition Voltages

The classical theory for the phenomenon of the is rejected as unsatisfactory, particularly as applied to solutions of heavy metal salts. It is suggested that in such cases the residual current is due to the discharge of hydrogen ions rather than metal ions. The discharge potentials of the tetraalkyl ammonium ions from methyl to amyl have been determined and, in general, found to increase with an increase in the number of carbon atoms. The decomposition voltages of zinc chloride, mercuric bromide, cadmium bromide and silver nitrate in pyridine have been determined and compared with those obtained in aqueous solution. Existence of a complex silver anion is indicated.