Showing papers in "Journal of Applied Electrochemistry in 1972"

Use of impedance measurements for the determination of the instant rate of metal corrosion

Abstract: The various methods of evaluating corrosion rate and charge transfer resistance have been critically reviewed on the basis of the recent developments on the measurement and interpretation of faradaic impedances. It is demonstrated that the entity which is most accurately correlated with corrosion rate is the transfer resistance, the limit of the faradaic impedance at infinite frequency. In the case of iron, with and without inhibitor (propargylic alcohol), it has been ascertained, under various experimental conditions, that the measurement of this resistance constitutes nowadays the best electrochemical test for corrosion, and allows thea priori calculation of corrosion rate.

High oxide ion conduction in sintered Bi2O3 containing SrO, CaO or La2O3

Abstract: Ionic conduction in sintered oxides of the system Bi2O3-SrO was investigated by measuring the conductivity and ion transference number under various conditions. The ion transference numbers were measured by an oxygen concentration cell employing the specimen as the electrolyte.

Electrochemical removal of copper ions from very dilute solutions

Abstract: A device for concentrating electropositive cations using porous, fixed, flow-through, carbon electrodes is described. A feed of 667μg of copper per ml of solution was reduced to less than 1μg of copper per ml of solution. The flow rate was 0.20 cm3/cm2/min through a bed 6 cm thick. Capital cost for the cell is the controlling factor. A preliminary economic analysis indicates that the value of copper recovered will more than pay for the installation and operation of the cell, even for fairly small units.

Proton migration in solids

Abstract: Experimental methods which are suitable for the study of proton migration in solids are discussed. Special attention is paid to the determination of the transport numbers of protons. A survey is given of the relevant properties of most materials for which proton migration has been claimed.

Anodic discharge of chloride ions on oxide electrodes

Abstract: The behaviour of a mixed oxide coating thermally deposited on titanium has been examined with respect to the anodic discharge of chloride ions.

Ionic mass transfer in parallel plate electrochemical cells

Abstract: Experimental investigations have been made of ionic mass transfer in a parallel plate electrochemical cell under both laminar and turbulent flow. The results obtained in the laminar flow region were found to be well represented by a Leveque-type equation modified to include the cell aspect ratio as an additional parameter. The influence of decreased mass transfer at the edges of the electrodes due to changes in the velocity profile was found to be small. For the turbulent region, there is a correlation of the mass transfer coefficient with Reynolds number to an exponent of 0.875 and Schmidt number to exponent of 0.21. This is in accord with existing correlations for heat and mass transfer in similar geometries over the range studied.

The efficiency of chlorine evolution in dilute brines on ruthenium dioxide electrodes

Abstract: The efficiency of chlorine evolution from dilute brines (0.5–0.1m) was studied on RuO2 and IrO2 coated Ti anodes at 20°C and 70°C. Efficiencies are generally much higher than on graphite electrodes. However at low current densities at 70°C the efficiency on RuO2 is considerably lower than on IrO2.

Carbon electrodes: Part 1. Hydrogen evolution in acidic solution

Abstract: The hydrogen evolution reaction has been studied using electrodes of vitreous carbon and graphite. The relative activity of the surfaces in promoting the hydrogen evolution reaction was found to be pyrolytic edge ≈ vitreous carbon > pyrolytic face. Comparative measurements of the double-layer capacitances indicate that relative activity cannot be entirely explained in terms of relative surface areas. The activity of the surfaces was found to be very sensitive to electrode pretreatment. Kinetic parameters are presented for the hydrogen evolution reaction on these carbons.

Engineering aspects of hydrazine-air fuel-cell power systems

Abstract: Over the last few years a number of fuel-cell power systems of various types and power outputs have been built by Shell Research Ltd. The first of these was a relatively primitive hydrazine-air system built in 1962. The paper will trace the development of these power systems from 1962 to the present day. Emphasis will be placed mainly on the engineering design and development that have been needed to take advantage of the improved catalysts and electrodes. Thus, the methods devised to give adequate fluid flows will be outlined, the simplification of components will be considered and the design of ancillaries will be discussed. Present-day fuel batteries have power densities of up to 130–150 W/kg (60–70 W/lb) and, even with commerically available auxiliaries, complete power systems having power/weight ratios of about 52 W/kg (24 W/lb) can be built. These figures are compared with the power densities of conventional electric generators, and future possibilities are discussed.

Electrosynthesis of adiponitrile in undivided cells

Abstract: It has been shown that adiponitrile can be synthesized in undivided cells under favourable conditions. Because of strong decomposition of the quaternary ammonium salt support electrolyte, its concentration must be kept at a very low level. To avoid excessive resistance of the cell, the distance between the electrodes must then be smaller than 0·5 mm. We have developed various types of such cells. The ‘capillary gap cell’ is simple in design and can be readily scaled up. Continuous operation is possible. Yields of about 90% of adiponitrile have been obtained. The energy consumption is less than 3 kWh/kg product. Work up of the solutions is greatly facilitated by the low salt concentrations. It has been shown that the anodic oxidation of isopropanol, which is used as cosolvent, is strongly influenced by the acrylonitrile present. A substantial portion of the isopropanol is oxidized to CO2.

The electrodeposition of aluminium from molten aluminium chloride/sodium chloride

Abstract: The electrodeposition of aluminium from an AlCl3/NaCl melt (80 wt % purified A1C13, 20 wt % NaCl at 175°C) has been studied and conditions established for the production of good quality electroplate on steel. To obtain a coherent, dendrite-free plate at current densities up to 16 mA/cm2, the presence of not less than about 0.07 wt % hydrogen chloride was found to be essential. Under these conditions the current efficiency was 85%. Continued plating resulted in a progressive increase in current efficiency up to practically 100% and a progressive deterioration in plate quality. Addition of more HCl at this stage restored the original conditions.

Zinc passivation and the effect of mass transfer in flowing electrolyte

Abstract: Passivation times,t p, of a zinc sheet anode have been found to vary from 2 min to 2 h over the experimental range of electrolyte velocities (0.075 to 0.20 ms−1), current densities (3,160 to 1,675 A m−2) and electrolyte temperature (298 to 333 K). Fort p longer than about 40 min there was a change in the nature of the experimental dependence oft p on the electrolyte flow rate and the current density. A satisfactory theoretical model of the dissolving zinc anode involving the diffusion of the soluble species through a growing porous solid layer on the electrode surface and through the electrolyte diffusion layer has been formulated to explain the dependence oft p on the experimental variables.

Recent advances in lithium solid state batteries

Abstract: The most recent studies of solid state batteries, based on lithium conducting electrolytes and capable of operating at room temperature, are reviewed. This type of battery is of particular technological interest since, theoretically, it possesses high voltage and high specific energy. Unfortunately the known lithium electrolytes have low specific conductivities and consequently the cells so far developed exhibit high internal resistance. In recent years, however, there has been a great effort to overcome this shortcoming, as pointed out in this paper. The review, therefore, is intended to provide the reader with an entree into this particular and important aspect of solid state battery technology.

The preparation and characterization of high performance Ag/C oxygen electrocatalysts

Abstract: The factors influencing the spatial distribution of metal catalyst on catalyst substrates have been investigated by studying the wettability, drying process and chemical interaction between the catalytic metallic salt solution and substrate, using AgNO3/graphite as a model system. AgNO3 reacts with graphite at temperatures above 100°C and hence very uniform dispersion of Ag on graphite is achieved by simple thermal treatment. On the other hand, for other systems which do not involve chemical reaction, such as H2PtCl6/graphite, freeze-drying gives better results. Teflon bonded electrodes prepared from impregnated catalysts containing 10% Ag on C gave 800m A/cm2 at 0·84 V for the reduction of oxygen in 5nKOH at room temperature.

Solid state ionics. High ionic conductivity solid in silver halide-silver sulphate system

Abstract: The ionic conductivities and phase diagrams of AgI-Ag2SO4, AgCl-Ag2SO4 and AgBr-Ag2SO4 systems have been studied with the help of electrical conductivity, transport number, DTA and X-ray studies. In the AgI-Ag2SO4 system, the solid solution of α-AgI with Ag2SO4 was quenched to room temperature to have high ionic conductivity of 5·0×10−2 (ohm. cm)−1 at room temperature and 1·3×10−3 (ohm. cm)−1 at −78°C. The quenched solid solution was stable at −20°C, but gradually decomposed toβ-AgI andβ-Ag2SO4 at room temperature. The transport number of silver ion in this solid solution was about 1·0. In the AgCl-Ag2SO4 and AgBr-Ag2SO4 systems, the electrical conductivity was of the order of 10−4 to 10−6 (ohm. cm)−1 at room temperature.

Evaluation of organic battery electrodes: Voltammetric study of the redox behaviour of solid quinones

Abstract: The redox behaviour of solid quinones has been examined by potential sweep and cyclic voltammetry. A number of quinones are insoluble in aqueous electrolytes and can be completely discharged and recharged without appreciable polarization, as found, for example, with solid chloranil (tetrachloro-p-benzoquinone) and solid duroquinone (tetramethyl-p-benzoquinone). Hence quinones are reversible redox systems not only in solutions but also in the solid state. During discharge and recharge in dilute sulphuric acid only slight polarization occurs, which is attributed to a pure diffusion overvoltage. Polarization is not much greater in salt solutions. In this case, however, the peaks of the voltammetric curves are broader. In ammonium chloride solutions a double peak corresponding to the two electron transfers is obtained for chloranil both anodically and cathodically; this shows that the semiquinone is stable in ammonium chloride solution. Duroquinone also gives two peaks, but these are observed only in non-stationary measurements so that they do not correspond to the state of equilibrium. The pH dependence of the redox potential is 59 mV per pH unit. Only chloranil in ammonium chloride solution shows two redox potentials, depending on the discharge depth, which are both lower than the potential corresponding to the pH. The possible application of quinones in secondary battery cathodes is discussed.

Preliminary studies on the electrolytic reduction of nitrobenzene to aniline

Abstract: The reduction of nitrobenzene by an electrolytic method is fairly simple and it does not require the complicated equipment needed in the vapour phase reduction method. On account of the simplicity of operation, an attempt is being made to work out a suitable electrolytic method for this tonnage of chemical and study its economics as compared to other known methods of production. In this paper, the results obtained in the preliminary experiments using the rotating electrode technique are discussed. It is found that it is necessary to add certain ‘hydrogen carriers’ to catalyse the reduction. Without the addition of such carriers, complete reduction is not possible. Various conditions such as current density, depolarizer ratio, temperature and concentration of the hydrogen carrier have been studied. An attempt is made to work out the material balance for the nitrobenzene employed.

The anodic oxidation of the binary compounds of the transition elements in sulphuric acid

Abstract: The anodic oxidation of the silicides and carbides of Ta, W and Mo in M H2SO2 has been studied. The rate of corrosion has been shown to be dependent on the solubility of the reaction products. Oxidation of the carbides of Ta and W produces a carbon rich surface. This may be an important factor in the enhanced catalytic activity for hydrogen oxidation shown by anodized tungsten carbide.

The effect of kinetic and hydrodynamic factors on current efficiency in the chlorate cell process

Abstract: An equation has been derived which relates the current efficiency of chlorate production to the operational parameters of the process and the constants connected with the events in the diffusion layer of the anode. The latter have been estimated using available literature data and the equation has been tested for the temperature dependence of current efficiency by comparison with experimental results. A fair degree of agreement has been achieved.

Electrolytic removal of oxygen from gases by means of solid electrolyte

Abstract: Nitrogen gas, containing controlled amounts of free oxygen and water or carbon dioxide, was de-oxidized by means of a solid oxide electrolyte tube at temperatures from 800 to 1000°C and at applied voltages of 0.5–3.0 V. The oxygen potential of the resulting gas mixture was measured simultaneously. The efficiency of the removal of oxygen, present in free or combined state, is shown as a function of the initial oxygen content\(P_{H_2 O}\),\(P_{CO_2 }\) temperature and applied voltage. The electrolysing current/applied voltage relationships obtained indicate that the resistance of the electrolysing circuit is mainly determined by the initial free oxygen content of the gas mixture. The behaviour of solid oxide electrolytes with externally applied potentials corresponding to pure ionic and mixed conduction is also discussed.

Anodic pickling of stainless steels in sulphuric acid

Abstract: Potentiostatic pickling in 20% aqueous H2SO4 was investigated on hot- and cold-rolled strips of stainless steels from industrial lines, in order to assess the potentiality of this technique. Experimental evidences for AISI Types 202, 304, 316, 410 and 430 are given. Optimum pickling conditions were defined on the basis of the potentiodynamic behaviour of oxidized specimens.

The performance of a forced-flow parallel plate electrochemical reactor with dilute solutions

Abstract: Experimental data relating to the performance of a fast flow parallel plate electrochemical reactor are reported, using very dilute reactant solutions. The results are shown to conform to the Chilton-Colburn analogy. The significance of such reactors, in terms of both electrochemical processing and treatment of dilute aqueous effluents, is discussed.

Studies on a new method of preparation of zinc sulphide useful for luminescent phosphors

Abstract: Hitherto the zinc sulphide material required for luminescent phosphors has usually been obtained by the reaction between a zinc salt and hydrogen sulphide. In this paper we report a new method of preparation of zinc sulphide by the reaction between thiourea and a zinc salt in an alkaline medium, at optimum conditions of pH. The zinc sulphide precipitate obtained under varying conditions of pH has been characterized by the methods of X-ray diffraction, electron microscopy and diffraction, optical microscopy, magnetic susceptibility, diffuse reflectance and density. A very important point which came out of these investigations is that with varying pH for the precipitating conditions, varying degrees of non-stoichiometry have been obtained. All these aspects have been discussed in terms of interstitial zinc atoms or Zn+ ions and electrons in anion vacancies.

Galvanic corrosion resulting from rupture of a protective metallic coating

Abstract: A treatment of corrosion of galvanic couples in which the area of one metal greatly exceeds that of the other has been carried out using mixed potential theory. A ruptured metallic coating on a metal substrate is encompassed by the treatment, as is a metal containing inclusions of a second metal as impurity. Two cases are examined. In the first, exemplified by zinc-plated steel, three reactions are considered: dissolution of the coating and reduction of the oxidizing agent on each metal. In this case, the result of the rupture is often a very marked increase in the corrosion of the coating, leading to an autocatalytic effect. The second case treats an active metal protected by a coating of a more noble metal. The following reactions are considered: both directions of the redox couple generated by the oxidizing agent, and the dissolution of the substrate. It is demonstrated that in the second case the corrosion rate is maximal at vanishingly small porosities. In both cases, variations of the corrosion potential can be used as a measure of porosity.

Anodic chlorate formation on platinized titanium

Abstract: The mechanism of anodic chlorate formation on platinized titanium was studied under well-controlled forced-convection conditions identical to those of previous experiments with graphite. Experimental results obtained in 4m NaCl and in 0·05m NaCl were compared to those predicted by mass transfer models describing anodic chlorate formation on graphite. In concentrated NaCl solution anodic chlorate formation rates for both electrode materials are smaller than expected for a diffusion controlled process. In dilute NaCl the ratio between measured rates and those predicted for diffusion control is shifted to higher values in qualitative agreement with predictions. Quantitative differences observed between the two electrode materials were attributed to the fact that hypochlorite oxidation on platinized titanium did not proceed at limiting current because of the slowness of the heterogeneous oxidation reaction.

Voltammetric investigations of negative lead battery electrodes: The effect of organic expanders

Abstract: By means of a continuous voltammetric sweep technique, the formation process of lead sheets in sulphuric acid can be investigated. Its behaviour depends strictly on the presence of certain organic substances. As an example, the effect of some expanders and other additives is demonstrated.

Mass exchange in a hydrogen-oxygen fuel cell with a capillary membrane

Abstract: The concentration and potential gradients across an electrolyte-containing membrane of the hydrogen-oxygen fuel cell have been calculated taking into account the following processes: diffusion of all solution components, ion migration in the electric field, permeation flux of the solution, external water vapour flows, water vapour transport in gas bubbles. A theory of the self-regulation of water removal has been developed, which takes account of the mass exchange conditions in the membrane and in the whole fuel cell, as well as the concepts of the buffer capacity of a fuel cell with a capillary membrane. The self-regulation of water removal during changes of the current or during changes of parameters influencing the rate of water removal, as well as the self-regulation in the case of a non-uniform process distribution over the electrode surface have been considered.

The mechanism of discharge of sintered plate cadmium electrodes

Abstract: Sintered plate Cd electrodes have been studied in alkaline solutions using potentiostatic and galvanostatic techniques The behaviour is, in many ways, similar to that of a flat Cd electrode A pseudo steady-state current is found due to the dissolution of Cd as Cd(OH)2−4 At more anodic potentials passivation occurs due to the solid state formation of Cd(OH)2 This model can account for the results obtained on galvanostatic discharge

Indirect high current density reductions using cathodically generated solvated electrons

Abstract: It is usually economically desirable in view of the high capital cost of plant and high interest rates, to perform electrosyntheses at high current densities. However, the rate of mass transfer often prevents the optimum value being achieved, particularly when the concentration of the substrate has to be kept low due to solubility or mechanistic reasons. Many attempts have been made to develop compact electrodes with large surface area to overcome this difficulty e.g. porous electrodes, slurry electrodes, particulate electrodes. In situations where indirect reaction is feasible, e.g. oxidation via a higher valency state of a transition metal [1], then a high current density can be achieved by using a high concentration of the intermediate, namely, the corresponding metal ion. The limiting factor then becomes the diffusion limited rate of mass transfer of the metal ion through the boundary layer. In the case of indirect reductions using electrochemically generated solvated electrons [2] the situation is even more favourable. Owing to the very high mobility of solvated electrons which, at high concentrations, is several orders of magnitude higher than for normal species [3], very high rates of electron transfer can be achieved through the stagnant boundary layer and gentle stirring suffices to balance this rate with the subsequent homogeneous reaction. Reductions using solvated electrons produced at very high controlled current densities in the presence of low concentrations of an organic substrate were performed in the hexamethylphosphoramide (HMPA)/lithium chloride