Showing papers in "Journal of Applied Electrochemistry in 1973"

Ionic conductivity of oxides based on Li4SiO4

Abstract: Lithium orthosilicate, Li4SiO4, and its solid solutions are a new group of solids of high ionic conductivity. Either Li or Si may be at least partially replaced by several other di-, tri- or tetra-valent cations. Highest conductivities were found for solid solutions with Si partially replaced by Ti; typical values were 10−3 to 10−4 Ω−1 cm−1 at 300°C rising toc. l Ω−1 cm−1 by 700°C. The solid solutions are easy to prepare and are stable in air. Conductivities were measured on pressed cubes of powdered material using variable frequency a.c. methods. The conductivities of these Li4SiO4 solid solutions are compared with those of other known Li-conducting solids; Li4SiO4 solid solutions are probably the best all-round, polycrystalline Li-electrolytes yet found for temperatures abovec. 200°C.

Carbon-air electrode with regenerative short time overload capacity: Part 1. Effect of manganese dioxide

Abstract: To increase the overload capacity of the carbon-air electrode in alkaline electrolyte, without seriously changing the electrode potential during short-time overload periods, small amounts of MnO2 were added to carbon and the effects investigated. The potentiodynamic investigations revealed the existence of two reducible manganese species with reduction potentials of about −280 mV and −400 mV. The second potential corresponds to the known reduction process Mn(III) → Mn(II) whilst the first one corresponds to a reversible process (the product is easily reoxidized by air or anodically), not reported in literature as yet. It was explained in terms of a new redox potential for the system Mn(III)/Mn(II), both species being strongly and irreversibly adsorbed at the carbon surface. The galvanostatic discharge curves in the absence of air indicate that a sufficient overload capacity of about 40 C cm−2 is available if 22% (wt) MnO2 is added. Steady-state polarization curves in the presence of air indicate the catalytic effect of small amounts of MnO2 for the oxygen reduction reaction.

Solid silver ion conductors

Abstract: Materials exhibiting high ionic mobilities in the solid state at room temperature have mainly been found in the silver ion conductors which are based on silver iodide. Though silver iodide is a low conductivity solid at room temperature, it exhibits high ionic conductivity at relatively higher temperatures. In order to stabilize this high conductivity phase of silver iodide at room temperature, the introduction of foreign cations or anions into the lattice of silver iodide has been attempted. In this paper, the various silver ion high conductivity solids are reviewed, together with those showing both high ionic and electronic conductivity.

A mathematical model for the porous lead dioxide electrode

Abstract: A theoretical model for the porous lead dioxide electrode is proposed on the basis of the macrohomogeneous model for porous electrodes. The structural changes during discharge, due to precipitation of lead sulphate, are considered. The two main structural effects, plugging of the pores and gradual insulation of the active electrode surface by the reaction product, lead sulphate, are both considered by relating them to the local degree of discharge. The numerical results show that, at high current densities, the discharge capacity is limited by both structural and transport restrictions. At the end of discharge a layer of lead sulphate crystals blocks the electrode surface in the outer layers of the electrode. The current can then neither be transferred across this insulated surface nor reach remaining active material in the inner parts of the electrode because of acid depletion, which is furthermore accelerated by the decreasing porosity.

Zinc-air cell with neutral electrolyte

Abstract: The zinc-air electrochemical system in 5m NH4Cl was studied. The optimum electrolyte-zinc ratio was found to be 50 ml g−1 Zn and the optimum electrolyte-cathode ratio, 15 ml cm−2 of carbon cathode. The air cathode polarization is not increased by intermittent usage of the cell. Electrodes made from zinc sponge with addition of lead show the smallest corrosion in the given electrolyte. The cell voltage is about 0.9–0.95 V at a load of 10 mA cm−2 of carbon cathode at ambient temperature.

Field crystallization of anodic films on tantalum

Abstract: The radial growth rate of crystalline areas during the anodization of tantalum is found to be related to the nature and concentration of both the solute and the solvent and also to the pH of the electrolyte. In general, the use of high solute concentrations or the addition of certain organic solvents produces reduced growth rates in aqueous electrolytes.

On the influence of the annealing temperature and heavy current treatments on the porous structure of platinum electrodes and on the kinetics of the oxygen reaction at high temperatures

Abstract: The influence of high temperature annealing and heavy current treatments of porous Pt electrodes is investigated with scanning electron microscopy. The results are discussed on the basis of the kinetic behaviour of these electrodes, known from the literature or deduced from our still unpublished results. It is demonstrated that both the structure and the catalytic activity are influenced by the treatments.

Electron micrographic examination of electrodeposited dispersion-hardened nickel

Abstract: Dispersion-hardened nickel has been produced by electrodepositing Ni from a Watts' bath containing Al2O3, TiO2 and ZrO2 particles (0.005–0.06μm) in suspension. The effect of these particles on the onset of recrystallization at elevated temperatures (up to 1400°C) has been studied and it has been shown that Al2O3 is the most effective in stabilizing the electrodeposited structure. Thin films of Ni-Al2O3 examined by transmission electron microscopy showed a high dislocation density and restricted twinning, the Al2O3 particles being present both within the grains and at the grain boundaries. For optimum thermal stability the oxide should be present in the nickel matrix as discrete particles, but electron microscopy has shown that in all cases agglomeration occurs and that the particles are present as large clusters. Attempts to avoid this difficulty have proved unsuccessful.

The electrochemical characterization of n-type gallium arsenide

Abstract: A method for determining the carrier concentration of n-type gallium arsenide by an electrochemical technique is described. The minority carrier diffusion length is also obtained, and using subsidiary measurements the minority carrier lifetime can be estimated. The extension of this treatment to the characterization of epitaxial layers is discussed.

High-rate plating of aluminium from the bath containing aluminium chloride and lithium aluminium hydride in tetrahydrofuran

Abstract: An electrolyte for the high-rate plating of aluminium from the tetrahydrofuran solutions of aluminium chloride and lithium aluminium hydride has been developed. A smooth and coherent deposit of aluminium has been obtained at the current density of 18 A dm−2 without stirring, whereas the conventional diethyl ether solvent bath allows good plating up to 5 A dm−2 under the same condition. The current densities applicable are increased with an increase in the molar fraction of aluminium chloride in tetrahydrofuran. The conductivity of the plating solution was measured at various molar ratios of aluminium chloride to lithium aluminium hydride. A plateau region of the conductivity curve plotted against the molar ratio is consistent with the composition of the plating bath giving a good plating. The plateau region is enlarged with an increase in total aluminium concentration.

An electrosynthesis of sulphones

Abstract: The cathodic reduction of SO2, dissolved in aprotic solvents, to the anion radical SO2− in the presence of organic halides RX results in the formation of organic sulphones R-SO2-R at appreciable current yields. With dihalides, polymeric sulphones or, as in the case ofo-xylylenedibromide, inner sulphinic esters (sultines) are formed, the latter being easily convertible to the corresponding cyclic sulphones.

Carbon electrodes with phthalocyanine catalyst in acid medium

Abstract: The catalytic properties of polymeric phthalocyanines with Fe and Co as central atoms for the electroreduction of oxygen in 0.5–2.3m H2SO4 were studied. No noticeable dependence of the electrode potential on the concentration of H2SO4 was found. The electroactivity of the catalyst with a central Fe atom undergoes considerable deterioration under the given conditions, whereas the stability of the catalyst with a central Co atom is very good and the potential of an electrode containing 30% catalyst in the active mass is 100 mV more positive than that of an electrode with 13% platinum, both at 40 mA cm−2. The electrode performance depends markedly on the sort of carbon substrate, showing a parallelism with respect to oxygen electrodes in alkaline medium. The gold mesh current collector can be replaced by the addition of carbon black to the active layer.

Cathodic polarization of pure iron in concentrated alkaline solution

Abstract: The potentiostatic pulse method was used to study the electrochemical evolution of hydrogen on polycrystalline iron electrodes in concentrated KOH solutions It was found that in pure KOH solutions there appeared to be two reaction mechanisms for hydrogen evolution, one at high the other at low overpotentials The addition of Li+, at constant hydroxide ion concentration, altered the kinetic parameters of these two mechanisms Furthermore in pure LiOH only one reaction mechanism for all overpotentials was observed

The effect of foreign atoms on the properties of electrolytic zinc powders

Abstract: Kinetic and morphological studies have been made of the deposition of zinc powder on steel substrate, from pure alkaline zincate electrolytes and with small amounts of lead and tin ions in the electrolyte. The rate of co-deposition of hydrogen has been followed volumetrically and the current efficiency of zinc deposition calculated as a function of potential.

Solid state ionics—the electrochemical analog memory cell with solid electrolyte

Abstract: A new type analog memory cell with variable output voltage has been proposed and its performance examined. The cell construction is $$\begin{gathered} {\text{Ag|RbAg}}_{\text{4}} {\text{I}}_{\text{5}} {\text{|(Ag}}_{\text{2}} {\text{Se)}}_{{\text{0}} \cdot {\text{925}}} {\text{(Ag}}_{\text{3}} {\text{PO}}_{\text{4}} {\text{)}}_{{\text{0}} \cdot {\text{075}}} {\text{|RbAg}}_{\text{4}} {\text{I}}_{\text{5}} {\text{|Ag}} \hfill \\ {\text{ }} \uparrow \hfill \\ {\text{ Pt}} \hfill \\ \end{gathered} $$ in which (Ag2Se)0.925(Ag3PO4)0.075 is a mixed conductor exhibiting high ionic and electronic conductivity at room temperature. The potential difference between the silver electrode and the platinum electrode depends on the silver activity in the mixed conductor, and it is changed by passing the current between one silver electrode and the platinum electrode. The output voltage of the cell is changed in the range of 150 to 0 mV. At open circuit, the memorized cell voltage decreased by only 1% over several hours.

An investigation into the recovery of zinc from zinc chloride-sodium chloride mixtures by electrolysis

Abstract: The electrolysis of zinc chloride-sodium chloride mixtures to yield zinc and chlorine has been examined. The optimum electrolyte composition was found to extend from 75% to 60% zinc chloride. In order to obtain the maximum current and energy efficiencies, it was found necessary to use horizontal electrodes with perforations to allow easy escape of the electrolysis products.

Solid state ionics—The ionic conductivity of the Ag2S-Ag1.70Te-AgX system (AgX; Ag4P2O7, Ag3PO4 and AgPO3)

Abstract: The thermal reaction products in the Ag2S-Ag1.70 Te-Ag4P2O7, Ag2S-Ag1.70 Te-Ag3PO4 and Ag2S-Ag1.70 Te-AgPO3 systems were found to exhibit both high ionic and electronic conductivity at room temperature. For example, the ionic conductivities of (Ag2S)0.69 (Ag1.70Te)0.285 (Ag4P2O7)0.025, (Ag2S)0.5(Ag1.70Te)0.45 (Ag3PO4)0.05 and (Ag2S)0.65 (Ag1.70Te)0.25(AgPO3)0.1 were 0.25, 0.25 and 0.22 (ohm. cm)−1 at 25°C, respectively. Differential thermal analysis and X-ray diffraction showed that these high ionic conductivity solids had an α-Ag2S-like structure at room temperature.

Double layer capacity of graphite in cryolite-alumina melts and surface area changes by electrolyte consumption of graphite and baked carbon

Abstract: The double layer (d.l.) capacity of pyrolytic graphite in cryolite-alumina melts at 1010°C was found to exhibit a minimum of 20μF cm−2 at 0·9 V positive to the aluminium electrode. The d.l. capacity attained a plateau of ∼60μF cm−2 at 1·1–1·4 V, while it rose steeply at potentials below 0·7 V. During electrolytic consumption involving CO2 evolution the d.l. capacity of pyrolytic graphite remained unaffected, while that of baked carbon was changed, reflecting changes in surface area. At low current densities (cds) the surface area increased substantially and the surface was noticeably roughened, while the opposite behaviour was observed at above 2.5 A cm−2.

Permselective membrane separators for organic electrolyte batteries

Abstract: The electrical resistances, transference numbers and Li+↔Cu++ and Br−↔ClO 4 − interdiffusion rates through a variety of cation-exchange and neutral membranes were measured in propylene carbonate (PC) solutions at 25°C. Of the 19 commercial and specially prepared membranes which were studied, the only membranes with electrical resistances in 0.50m LiClO4/PC low enough to be of further interest as separators for organic electrolyte batteries were the AMF C-322, Amicon UM-05, Ionac MC-3470 and Corning No. 7930 porous glass (0.25 mm thick). The resistances of these membranes were 117, 2.3×102, 3.4×102 and 75.0 Ω, cm2, respectively. In order to benefit from the reduced resistance of thin membranes without sacrificing mechanical strength, laminated phenolsulfonic acid-formaldehyde (PF) membranes consisting of a thin layer of cation exchange resin on an inert porous support were prepared. Interdiffusion measurements showed that the laminated PF membranes are a more effective diffusion barrier towards anions in PC solutions than a commercial ultrafiltration membrane, the Amicon UM-05. The anion inter-diffusion fluxes for Br− between 0.10m LiBr/PC and 0.10m LiClO4/PC through the PF and UM-05 membranes were 6.17×10−11 and 1.5×10−10 mole s−1 cm2, respectively.

Time optimal electrodeposition of metals with a pulsating current

Abstract: A method of input current shape synthesis, applied to the process of the electrodeposition of metals, is given. It is shown that the optimal control theory can be successfully applied to this kind of problem. Essentials of the mathematics of the method and the computer program flow chart are also given.

Carbon electrodes: Part 2. The anodic oxidation of N-propylamine

Abstract: The anodic oxidation of a primary aliphatic amine, n-propylamine, has been studied at electrodes of vitreous carbon and pyrolytic graphite. The electrode reaction has been found to differ greatly for the two materials, as evidenced by the voltammetric behaviour at rotating disc electrodes and the results of preparative electrolyses. The observations at the vitreous carbon electrode are in agreement with the mechanism proposed by Mann and Barnes for the oxidation of propylamine at a stationary platinum electrode. A novel mechanism is proposed for the oxidation at a pyrolytic graphite anode.

The effect of pH on graphite wear in a chlorate cell process

Abstract: An apparatus and a method for graphite wear investigation at constant pH values in a chlorate cell process have been developed and presented. The same set-up could also be used in a chlorine cell process. Experimental and compilative data show the existence of an optimal pH region providing minimal graphite consumption in electrolytic chlorate production. The latter also coincides with the same pH range which provides maximal rates of active chlorine chemical conversion into chlorate [1], and thereby maximal current yields as well. Therefore, by adjusting the pH, one simultaneously optimizes both the graphite wear and the whole electrolytic process.

Electrolysis of molten salt solutions containing PbSO4

Abstract: Low faradaic yields of Pb were found when electrolysing melts containing PbSO4 in solvents of either LiCl-KCl eutectic or Li2SO4-K2SO4-Na4SO4 eutectic and employing low current densities.

Anion distribution in alkaline silicates

Abstract: Alkaline sodium silicates have been prepared by heating sodium carbonate and silica mixtures in the mole ratio of 2.5∶1.

Cathodic polarization characteristics of poly (4-vinylpyridine) bromine complex

Abstract: The cathodic polarization characteristics of the electrode consisting of poly (4-vinylpyridine) bromine complex and graphite powder were investigated. The electrolyte was propylene carbonate containing 1 M LiBr. The rest potential of the electrode was approx. 0.5 V (versus SCE). The coulometric efficiency of the continuous discharge was 52–53%.

Effects of mercury on the surfaces of polycrystalline copper, tin and zinc

Abstract: Interfacial capacitance measurements have been used to study the effects of mercury on diamond polished copper, tin and zinc surfaces in 10M KOH. In the case of copper, microgram quantities of mercury were sufficient to inhibit the adsorption of hydrogen and reduce the surface heterogeneity. In contradistinction to copper, similar concentrations of mercury were found to increase the heterogeneity of tin and zinc surfaces. A decrease in surface heterogeneity for zinc was only observed at very high mercury concentrations. The increased surface heterogeneity is thought to arise from dissolution at the intercrystalline grain boundaries by mercury.

Prediction of metal distribution in electroplating systems

Abstract: Three methods of approximation were developed to predict the metal distribution in electroplating systems. The results were compared with Watson's experimental data for the Watts-nickel (close to 100% current efficiency), tin-nickel (alloy deposition, also close to 100% current efficiency), and the standard chromium (approximately 20% current efficiency) systems. Method 1 predicted too uniform a distribution whereas Methods 2 and 3 showed good agreements with all three systems. The same experimental data were also used to evaluate three predictive methods frequently used in the literature. The primary current distribution and an empirical formula by Hull were found to be inadequate in describing these systems. The secondary current distribution which involved a great deal of numerical analysis showed a considerable improvement.