Showing papers in "Journal of Applied Electrochemistry in 1979"
TL;DR: In this paper, a detailed structural investigation of Ni deposits obtained from a Watts solution, thanks to both X-ray diffractometry and electron-microscope techniques, leads to distinguish a free mode of growth, which is characterized by [100] oriented deposits, from several inhibited modes such as [110, [210], 〈211, and [111], and the two latter are stabilized by Ni(OH)2 while the two former are respectively due to atomic and molecular forms of adsorbed hydrogen.
Abstract: The electrocrystallization of Ni is known to be a highly inhibited process. This work gives some conclusions about the nature of the major inhibiting species. All of these species are formed in the catholyte because of the hydrogen codeposition. Depending on plating conditions, mainly pH and current density of metallic deposition, we observe a predominancy of a definite inhibitor which selectively promotes one mode of growth and leads to a deposit exhibiting definite structural properties. A careful structural investigation of Ni deposits obtained from a Watts solution, thanks to both X-ray diffractometry and electron-microscope techniques, leads us to distinguish a free mode of growth, which is characterized by [100] oriented deposits, from several inhibited modes such as 〈110〉, [210], 〈211〉 and 〈111〉. The two latter are stabilized by Ni(OH)2 while the two former are respectively due to atomic and molecular forms of adsorbed hydrogen.
230 citations
TL;DR: In this paper, the anodic behavior of chalcopyrite in 1 M H2SO4 and 1M HCl was studied by linear sweep voltammetry and potentiostatic electrolysis.
Abstract: The anodic behaviour of chalcopyrite in 1 M H2SO4 and 1 M HCl was studied by linear sweep voltammetry and potentiostatic electrolysis. Voltammograms with a fresh surface showed a small prewave, attributed to a surface oxidation process, followed by a region of active dissolution characterized by a steeply rising anodic current. At still higher potentials the behaviour differed in the two electrolytes, but, contrary to a previous report, there was no evidence of a photosensitive limiting current. Anodic characteristics of chalcopyrite specimens from different sources, including synthetic material, were similar. The anode reaction was found to involve 6·7±0·3 F per mole of chalcopyrite, from which it was calculated that 86% of the sulphide sulphur was oxidized to the elemental form (some of which was plastic sulphur) and 14% to sulphate. The surfaces of oxidized electrodes were examined and photographed after varying periods of potentiostatic electrolysis. Chalcopyrite dissolution occurred at localized sites, the number of which depended strongly on potential. Current-voltage and potentiostatic current-time curves were interpreted in terms of the kinetics of nucleation, growth and overlap of these discrete corrosion centres.
103 citations
TL;DR: In this paper, the development of solid polymer electrolyte (SPE) water electrolysers, increasing the operating temperature of alkaline water electrolyservers from 80° C to a temperature in the range 120°C to 150°C, is discussed.
Abstract: Efforts to improve water electrolysis technology are being made using three promising approaches: (a) development of solid polymer electrolyte (SPE) water electrolysers, (b) increasing the operating temperature of alkaline water electrolysers from 80° C to a temperature in the range 120–150° C, and (c) investigation of advanced concepts. The research and development efforts on SPE water electrolysers are aimed at (a) low cost current collectors, (b) high-activity electrocatalysts, (c) high temperature capability, (d) low cost SPE, and (e) design and construction of scaled-up cell stacks. Attempts are being made to find materials for cells and auxiliaries which are stable in an alkaline environment at elevated temperatures. Advanced concepts for electrolytic hydrogen production, including (a) finding better reversible electrocatalysts, (b) use of anode depolarizers, (c) water vapour electrolysis in molten or solid electrolytes, (d) development of hydroxyl ion transporting membranes, (e) investigation of thermochemical-electrochemical hybrid cycles, and (f) photoelectrolysis of water, are still at a preliminary research stage.
101 citations
TL;DR: In this article, a trickle bed electrochemical reactor has been developed for the production of dilute alkaline peroxide solutions by reduction of oxygen, and the effects of current density, oxygen pressure and flow rate, electrolyte concentration, graphite particle size, bed thickness and length were investigated.
Abstract: A trickle bed electrochemical reactor has been developed for the production of dilute alkaline peroxide solutions by reduction of oxygen. Oxygen gas and sodium hydroxide flow concurrently downward through a cell which consists of a thin packed cathode bed of graphite particles separated from the anode plate by a porous diphragm. Current flows perpendicular to the flow of electrolyte. The effects of current density, oxygen pressure and flow rate, electrolyte concentration and flow rate, graphite particle size, bed thickness and length were investigated. In 2 M NaOH peroxide solutions of 0.8 M have been produced at 60% efficiency with current densities of 1200 A m−2 and cell voltages of 1.8 V. A bipolar cell stack consisting of five cells has been tested.
79 citations
TL;DR: In this paper, the problem of non-destructive determination of the state of charge of nickel-cadmium batteries has been examined experimentally and theoretically from the viewpoint of internal impedance, and it is shown that the modulus of the impedance is mainly controlled by diffusion at all states of charge.
Abstract: The problem of nondestructive determination of the state-of-charge of nickel-cadmium batteries has been examined experimentally as well as theoretically from the viewpoint of internal impedance. It is shown that the modulus of the impedance is mainly controlled by diffusion at all states of charge. Even so, a prediction of the state of charge is possible if the equivalent series/parallel capacitance or the alternating current phase shift is measured at a sufficiently low a.c. test frequency (5–30 Hz) which also avoids inductive effects. These results are explained on the basis of a uniform transmission-line analog equivalent circuit for the battery electrodes.
69 citations
TL;DR: In this article, a relationship was shown between the effect of lead contamination on zinc deposit morphology and orientation and on the overpotentials associated with zinc electrodeposition in the presence of lead.
Abstract: Zinc deposits contaminated with lead were found to have characteristic morphologies and orientations which were dependent on the amount of lead present in the zinc deposits and to a lesser extent on the presence of other impurities such as antimony and glue in the deposits. Increasing lead in the zinc deposits progressively changed the orientations from (1 1 2) to (1 0 1) to (1 0 0) to finally a poorly crystalline (0 0 2) structure. The lead content of the zinc deposits was dependent on both the concentration and chemical composition of lead added to the electrolyte, the current density and also on the presence of antimony or glue in the electrolyte. A relationship was shown to exist between the effect of lead contamination on zinc deposit morphology and orientation and on the overpotentials associated with zinc electrodeposition in the presence of lead.
60 citations
TL;DR: In this article, the electrode kinetics of spongy and dendritic zinc deposition were studied in the presence of three inhibitors (lead acetate, tetrabutylammonium bromide and benzalacetone).
Abstract: The electrode kinetics of spongy and dendritic zinc deposition were studied in the presence of three inhibitors (lead acetate, tetrabutylammonium bromide and benzalacetone). It was shown that these additives increase the cathodic overvoltage, decrease the current efficiency, eliminate multiple steady states in acid electrolytes, and modify the impedance diagrams. Such changes in electrode kinetics were interpreted in terms of weaker autocatalytic adsorption of metal cations and enhanced hydrogen adsorption. It was also shown that a pH decrease had a similar effect on these reaction rates. It was concluded from very low frequency impedance measurements that the additives give rise to an accelerated nucleation rate ensuring a faster renewal of active growth sites.
56 citations
TL;DR: In this paper, the authors interpreted the Ni(OH)2 reaction as two parallel electron transfer steps coupled to two chemical reactions through a square-type reaction model, and estimated the rate of the chemical change.
Abstract: The electrochemical reaction Ni(OH)2=NiOOH+H++e occurring under potentiodynamic conditions in 1 N KOH using complex triangular potential sweep revealed the existence of non-equilibrium effects of both reactant and products which cause the splitting of the anodic current peak already known. By a suitable choice of the perturbation variables, the rate of the chemical change the Ni(OH)2 species undergoes can be estimated. The reaction presenting the nickel hydroxide electrode is interpreted as two parallel electron transfer steps coupled to two chemical reactions through a square-type reaction model.
54 citations
TL;DR: In this article, it was shown that the internal impedance of a lead-acid battery is controlled by charge transfer and diffusion processes in the frequency range 15-100 Hz. But this was based on a uniform transmission line analog equivalent circuit for the battery electrodes.
Abstract: The determination of the state-of-charge of the lead-acid battery has been examined from the viewpoint of internal impedance. It is shown that the impedance is controlled by charge transfer and to a smaller extent by diffusion processes in the frequency range 15–100 Hz. The equivalent series/parallel capacitance as well as the a.c. phase-shift show a parabolic dependence upon the state-of-charge, with a maximum or minimum at 50% charge. These results are explained on the basis of a uniform transmission-line analog equivalent circuit for the battery electrodes.
46 citations
TL;DR: In this paper, it was argued that, regardless of the degree of purity achieved, hydrogen must always be produced simultaneously with zinc, and that when impurities are present, the current efficiency falls progressively as electrodeposition proceeds.
Abstract: In the electrodeposition of zinc from acidified zinc sulphate solutions the loss in current efficiency (CE) due to evolution of hydrogen at the cathode has often been attributed to the presence of metal impurities, and it has been thought that in a pure solution the CE would be 100%. In this paper it is argued that, whatever the degree of purity achieved, hydrogen must always be produced simultaneously with zinc. At the start of electrolysis the CE is determined solely by the zinc/acid ratio, but when impurities are present the CE falls progressively as electrodeposition proceeds. Further, colloid silica which is always present in plant solutions is not responsible for the CE falling below 100%, nor are the lead anodes that are used in practice. Some effects of manganese, both at the anode and the cathode, are reported. The deleterious influences of cobalt and manganese together are also discussed.
46 citations
TL;DR: In this article, the voltaic performance of the zinc-chlorine battery was investigated by measuring the individual potentials of the Zn and Cl2 electrodes versus a reference electrode.
Abstract: The voltaic performance of the zinc-chlorine battery was investigated by measuring the individual potentials of the Zn and Cl2 electrodes versus a reference electrode. The overpotential at the Zn electrode is very small for both the charging and the discharging processes, and the use of a flow-through porous Cl2 electrode is advantageous. Energy efficiency in the region of 65% has been achieved for a complete cycle. Tafel polarization data for both the zinc and the Cl2/graphite electrodes was obtained using rotating zinc hemisphere and graphite disc electrodes. Exchange current densities and Tafel slopes are reported.
TL;DR: In this paper, a study of the electrodeposition of nickel onto copper and graphite is described; the objective was to prepare high surface area, i.e. microrough, but stable deposits which could be used as nickel oxide anodes in aqueous base.
Abstract: A study of the electrodeposition of nickel onto copper and graphite is described; the objective was to prepare high surface area, i.e. microrough, but stable deposits which could be used as nickel oxide anodes in aqueous base. It is shown that such electrodes may be prepared by electrodeposition at a high current density (200 mA cm−2) from a Watts bath and that they give useful apparent current densities for a model synthetic reaction, the oxidation of ethanol to acetic acid.
TL;DR: In this article, the authors proposed a square-type reaction scheme to interpret the behavior of the nickel hydroxide electrode in KOH solutions under non-equilibrium conditions, which includes electrochemical as well as chemical crossed reactions between the different transient species.
Abstract: The square-type reaction scheme proposed to interpret the behaviour of the nickel hydroxide electrode in KOH solutions under non-equilibrium conditions must include electrochemical as well as chemical crossed reactions between the different transient species. These reactions are evidenced by means of the triangularly-modulated triangular potential sweep technique. The contribution of the crossed reactions in the square-type reaction scheme becomes more relevant as the KOH concentrations decreased in the presence of K2SO4 supporting electrolyte.
TL;DR: Limiting currents were measured for the electropolishing of horizontal copper electrodes facing downwards in phosphoric acid solution under natural convection conditions in this paper, where the electrode diameter was varied from 1-6 cm and the acid concentration between 8-12 M. The limiting current was initially to decrease with electrode diameter and then to remain constant with further increase.
Abstract: Limiting currents were measured for the electropolishing of horizontal copper electrodes facing downwards in phosphoric acid solution under natural convection conditions. The electrode diameter was varied from 1–6 cm and the phosphoric acid concentration between 8–12 M. The limiting current was found initially to decrease with electrode diameter and then to remain constant with further increase. Within the concentration range of phosphoric acid used, the limiting current was found to decrease with phosphoric acid concentration. Mass transfer data was found to agree closely with the equation
$$(Sh) = 0 \cdot 18[(Sc)(Gr)]^{0 \cdot 33} for 1 \cdot 1 \times 10^9< (Sc)(Gr)< 2 \cdot 46 \times 10^{11} .$$
TL;DR: Zinc deposits electrowon from synthetic zinc chloride electrolyte were characterized by a morphology which featured clusters of large platelets with rounded edges and a preferred crystallographic orientation as mentioned in this paper.
Abstract: Zinc deposits electrowon from synthetic zinc chloride electrolyte were characterized by a morphology which featured clusters of large platelets with rounded edges and by a preferred crystallographic orientation, namely (0 0 2) (1 0 3) (1 0 5). These deposit characteristics persisted over a wide range of experimental conditions which included variations in the current density and changes in anode material, cell design, and the zinc and hydrochloric acid concentrations. Although the addition of HCl to the electrolyte improved the physical characteristics of the deposit, it did not alter the deposit morphology or orientation. The addition of animal glue or tetrabutylammonium chloride resulted in smooth, compact deposits having a (1 1 0) orientation at 0·24 M H+. Jaguar C-13 additions gave a (1 1 2) orientation, while gum arabic and tetraethylammonium chloride only affected the grain size. The various deposit morphologies and orientations obtained showed only some correspondence to changes occurring in the zinc deposition polarization voltages. The presence of metallic impurities, Cu, Co, Fe, and Sb, caused the morphology and orientation of the deposits to become more basal and the current efficiency to decrease. The presence of Cd resulted in a (1 1 2) (1 1 4) orientation and Pb gave a (1 0 1) orientation.
TL;DR: In this paper, the influence of underpotential Pb and Tl-adsorbates at rotating disc silver single crystal surfaces (111), (100), and (110) on the kinetics of redox reactions was studied in 0.5 M NaClO4 and 0.6 M Na2SO4 solutions (2 < pH < 4).
Abstract: The influence of underpotential Pb- and Tl-adsorbates at rotating disc silver single crystal surfaces (111), (100), and (110) on the kinetics of ‘outer-sphere’ and ‘inner-sphere’ redox reactions was studied in 0.5 M NaClO4 and 0.5 M Na2SO4 solutions (2 < pH < 4) containing Fe3+, Ce4+ or NO
3
−
ions. While the reduction of Fe3+ and Ce4+ under limiting diffusion conditions was not affected by the metal adsorbates, a strong inhibition effect correlated to the degree of Pb- or Tl-adsorbate coverages was observed in the case of the reduction process in the presence of NO
3
−
ions. The results are interpreted in terms of a strong chemical interaction between the reactant or a reaction intermediate and the silver substrate, taking into account the previously proposed superlattice structures of the metal adsorbates, depending on the orientation of the silver single crystal surfaces and on the underpotential range.
TL;DR: The influence of PbO modification on the formation of 4PbO·PbSO4 paste was determined by X-ray diffraction analysis and scanning electron microscopy as discussed by the authors.
Abstract: The influence of PbO modification on the formation of 4PbO·PbSO4 paste is determined by X-ray diffraction analysis and scanning electron microscopy. The paste was prepared from tetragonal PbO, orthorhombic PbO and several mixtures of both oxides at 80° C and a H2SO4/PbO ratio of 6 wt%.
TL;DR: In this article, the electrolysis at an iron anode of water-methanol (20-30 vol%) solutions containing phenol as the main monomer and small amounts of a substituted phenol (generallyo-chlorophenol) and ethylenediamine leads to thick and adhesive polyoxyphenylene coatings on the electrode surface.
Abstract: The electrolysis at an iron anode of water-methanol (20–30 vol%) solutions containing phenol as the main monomer and small amounts of a substituted phenol (generallyo-chlorophenol) and ethylenediamine leads to thick and adhesive polyoxyphenylene coatings on the electrode surface. The yield of polymer indicates that 2F mol−1 of phenol are transferred in the polymerization: the thickness of the deposit depending on both the applied potential and the composition of the solution. Thus in such systems it is possible in a single-step to attain preparation of the polymer and its deposition as a cross-linked highly insoluble protective film onto Fe articles.
TL;DR: In this paper, the morphology of dislocation-free {211} iron surfaces during electrochemical dissolution and measurements of distances and directions of monatomic steps provide information about the rates and potential dependences of three different elementary processes involving iron atoms bound to the lattice in three geometrically and energetically different states.
Abstract: The quantitative analysis of the morphology of dislocation-free {211} iron surfaces during electrochemical dissolution and measurements of distances and directions of monatomic steps provide information about the rates and potential dependences of three different elementary processes involving iron atoms bound to the lattice in three geometrically and energetically different states. The interaction of the three elementary processes explains the well-known anomalies of the kinetics of the iron electrode. A statistical analysis of the step distances is given.
TL;DR: In this article, the effect of cadmium on cathodic zinc crystal growth was studied in high purity industrial electrolyte, with and without additives, in an attempt to establish a correlation between morphology, polarization and the extent of Cadmium contamination.
Abstract: The effect of cadmium on cathodic zinc crystal growth was studied in high purity industrial electrolyte, with and without additives, in an attempt to establish a correlation between morphology, polarization and the extent of cadmium contamination. Cadmium additions to acid zinc sulphate electrolyte did not have a significant effect on the zinc deposit orientation but did substantially refine the deposit grain size. The refinement in deposit grain size is directly related to the level of cadmium in the zinc deposits. Cadmium, in combination with glue and optimum amounts of glue and antimony, also reduced the deposit grain size: the preferred deposit orientation remained (1 1 2) with a slight tendency to (1 0 1) at high glue concentrations. Cadmium in combination with antimony resulted in an increased depolarization of zinc deposition and a basal (0 0 2) deposit orientation. Lead additions to zinc electrolyte containing cadmium resulted in increased deposition overpotentials and intermediate to vertical deposit orientations.
TL;DR: In this article, mass transfer characteristics and their applicability to flow-dependent corrosion processes and erosion corrosion are discussed with regard to mass transfer properties and their application to materials selection for seawater pumps, corrosion data of non-alloyed and low alloy cast iron are presented.
Abstract: Flow-dependent corrosion phenomena can be studied in the laboratory and on a pilot plant scale by a number of methods, of which the rotating disc, the rotating cylinder, the coaxial cylinder and the tubular flow test are the most important. These methods are discussed with regard to mass transfer characteristics and their applicability to flow-dependent corrosion processes and erosion corrosion. To exemplify the application of such methods to materials selection for seawater pumps, corrosion data of non-alloyed and low alloy cast iron are presented.
TL;DR: In this paper, the difference between surface roughness amplification and dendritic growth in copper electrodeposition in the limiting current density range was shown, and the critical overpotential of copper dendrite growth was determined as 550 mV.
Abstract: The difference between surface roughness amplification and dendritic growth in copper electrodeposition in the limiting current density range is shown. The critical overpotential of copper dendrite growth is determined as 550 mV.
TL;DR: In this paper, the electrodeposition of hard gold in layers of 2 μm was investigated, and the electrolyte was an acid citrate bath (pH 3·5) with cobalt as an additive.
Abstract: The electrodeposition of hard gold in layers of 2 μm was investigated. The electrolyte was an acid citrate bath (pH 3·5) with cobalt as an additive. A flow cell allowed a controlled variation of the hydrodynamic conditions. The following features were examined quantitatively in the experiments: the current efficiency for gold deposition (10–30%), the carbon and cobalt content, as well as the porosity of the deposits, and the morphology [by scanning electron microscope (SEM)]. Above 50 mA cm−2 the deposition of gold and to a minor extent the incorporation of cobalt become mass transport limited (with certain complications resulting from the complex nature of the diffusion layer). The influence observed below 50 mA cm−2 seems to be due to the synergic effect of the transport controlled reduction of dissolved oxygen. A simple qualitative model for the incorporation of carbon is proposed. The substantial decrease in current efficiency observed upon the addition of cobalt to the bath is probably causedboth by a decrease of the hydrogen overpotential and by an increase of the overpotential for gold deposition. From the viewpoint of technical application, the most relevant result, is the substantial decrease in porosity at decreasing current density (c.d.) and increasing flow rate.
TL;DR: In this paper, the anodic dissolution of gold in concentrated potassium cyanide solution was studied and four regions of passivation were observed: at -0·6 V, +0·1 V, −0·4 V and − 0·7 V versus SCE.
Abstract: The anodic dissolution of gold in concentrated potassium cyanide solution was studied. Four regions of passivation were observed: at -0·6 V, +0·1 V, +0·4 V and +0·7 V versus SCE. The passive phenomena were explained in terms of the interaction of hydroxyl ions with the gold surface.
TL;DR: The critical overpotential for zinc dendrite growth is determined as 173 mV by the method described by Popovet et al. as mentioned in this paper, which can be applied successfully to metal deposition processes when there is a large codeposition of hydrogen.
Abstract: The critical overpotential for zinc dendrite growth is determined as 173 mV by the method described by Popovet al. [1]. It was shown that this procedure can be applied successfully to metal deposition processes when there is a large codeposition of hydrogen.
TL;DR: A review of the current status of electrodeposited coatings from molten salts, with special reference to diffusion coatings on metal and alloy surfaces, is presented in this paper, where the available physical, chemical, and mechanical properties of the coatings thus formed and their applications are summarized.
Abstract: Electrolytic deposition processes from molten salt baths, i.e. metalliding and electroplating, for coating metal or alloy substrates are described. An outline of the general experimental techniques employed in molten salts and the influence of various factors such as impurities, cation valency, nature of the solvent, stability of complex ions, temperature, current density, kinetics, and additives, on the electrolytic processes are discussed. A review of the current status of electrodeposited coatings from molten salts, with special reference to diffusion coatings on metal and alloy surfaces, is presented. The available physical, chemical, and mechanical properties of the coatings thus formed and their applications are summarized. Some suggestions are made to show the directions in which further research in this field is necessary.
TL;DR: In this article, low frequency impedance measurements reveal an inductive loop associated with a diffusion-controlled inhibition of electrodeposition of zinc and nickel, and it has been concluded that this loop arises from a coupling between the inhibitor diffusion and interfacial processes slower than diffusion.
Abstract: At low rotation speeds of a rotating disc electrode the diffusion-controlled inhibition of zinc deposition by lead acetate or tetrabutylammonium bromide emphasizes the existence of multiple steady states. With both zinc and nickel deposition, low frequency impedance measurements reveal an additional inductive loop associated with a diffusion-controlled inhibition of electrodeposition. From the relaxation time constant it has been concluded that this loop arises from a coupling between the inhibitor diffusion and interfacial processes slower than diffusion and involving, at least for zinc deposition, the slow renewal of active growth sites.
TL;DR: In this paper, a reduction of aldehyde to alcohol by OH radicals was shown when H2O2 was produced in excess over Fe(II), and a remarkable increase of the yields was observed.
Abstract: OH radicals, produced in aqueous acid media by the electrogenerated system Fe(II)/H2O2, promote the oxidation of polymethylated benzenes. Under our experimental conditions only one -CH3 group was oxidized to -CHO. A reduction of aldehyde to alcohol by.OOH radicals was shown to occur when H2O2 was produced in excess over Fe(II). In hydrochloric acid or in perchloric acid with Cl− ions added, a remarkable increase of the yields was observed. The results are discussed on the basis of the kinetic parameters of the reactions involved in the process.
TL;DR: In this paper, a study of the electrochemical fluorination of octanoic acid halides has been made using techniques involving careful "preparation" of the anodes prior to the introduction of organic substrate, followed by fluorination under controlled conditions.
Abstract: A study of the electrochemical fluorination of octanoic acid halides has been made using techniques involving careful ‘preparation’ of the anodes prior to the introduction of organic substrate, followed by fluorination under controlled conditions. Studies were conducted on both bench scale and pilot plant scale operations. Reaction parameters are described in detail. The principal products were perfluorooctanoyl fluoride and a mixture of perfluorocylic ethers. The experiments established that reproducibility of the results could be achieved and that, by proper attention to reaction conditions, breakdown of the carbon skeleton was minimized; the variation of product ratios could be regulated to optimize the yield of desired materials.
TL;DR: In this paper, the early stages of metal deposition are controlled by a three-dimensional nucleation followed by hemispherical growth, and the deposit morphology has been confirmed by scanning electron microscopy (SEM).
Abstract: The electrodeposition of lead onto a glassy carbon electrode from 0·1m HCl solution has been studied mainly by potential step techniques. The early stages of metal deposition are shown to be controlled by a three-dimensional nucleation followed by hemispherical growth. The deposit morphology has been confirmed by scanning electron microscopy (SEM). Results obtained by linear sweep voltammetry are also reported and qualitatively interpreted according to the above-mentioned nucleation mechanism.