Showing papers on "Overpotential published in 1981"
TL;DR: In this article, the point defect model was extended to account for chemical breakdown, and the dependence of the breakdown potential on halide concentration and incubation time breakdown overpotential relationships was investigated.
Abstract: The point defect model that was previously developed (1) to explain the growth kinetics of a passive film has been extended to account for chemical breakdown. This model provides quantitative explanations of the dependence of breakdown potential on halide concentration, and of the incubation time‐breakdown overpotential relationships that have been observed for iron and nickel in aqueous solutions. Limitations of the model are identified and discussed.
551 citations
TL;DR: In this paper, the initial electrocatalytic activity for oxygen evolution in acid electrolyte was determined using the potentiostatic method, and the surface areas of these oxides were estimated using cyclic voltammetry.
Abstract: Ruthenium oxide, prepared by the thermal decomposition method, has the highest known initial electrocatalytic activity for oxygen evolution in acid electrolyte. However, this material is not stable in the electrolyte and at the same time exhibits a significant increase of oxygen overpotential with time, probably due to a chemical transformation of the oxide from a lower to a higher valence state. Efforts were made to stabilize ruthenium by preparing mixed oxides with Ir and/or Ta using the thermal decomposition method. The electrocatalytic activities for oxygen evolution on these oxides in were determined using the potentiostatic method. The surface areas of these oxides were estimated using cyclic voltammetry. Dual Tafel slopes (approximately 30 and 40 mV) were found on most of these oxides. The ternary oxide exhibited a single Tafel slope of 30 mV, had the lowest overpotential, and showed minimum variation of overpotential with time.
110 citations
IBM1
TL;DR: The mechanism responsible for very high plating rates at electrodes illuminated by a laser beam was investigated in this article, where the authors measured the enhancement in plating rate as a function of overpotential, laser power, and substrate thickness and compared these results with measurements using solutions at various bulk temperatures.
Abstract: The mechanism responsible for the very high plating rates at electrodes illuminated by a laser beam was investigated. Absorption of the laser energy by the electrode results in a localized increase in temperature at the metal‐solution interface. This leads to: (i) a shift in the rest potential, (ii) an increase in the charge transfer rate, and (iii) strong microstirring of the solution due to thermal gradients and, at high laser power densities, to strong local boiling. Verification of the first two effects was achieved by measuring the enhancement in plating rates as a function of overpotential, laser power, and substrate thickness and by comparing these results with measurements using solutions at various bulk temperatures. Observation of the cathode through a video monitor, as well as detection of bubble formation using a miniature microphone, verified that a correlation exists between the ejection of bubbles from the cathode and sharp increases in the current. Application of laser‐enhanced electroplating for maskless generation of patterns is also briefly discussed.
100 citations
TL;DR: In this paper, the evolution kinetics on iridium anodes on which oxide films of various thicknesses from a monolayer upwards were formed by a potential cycling program, were reported.
Abstract: Studies of evolution kinetics on iridium anodes on which oxide films of various thicknesses from a monolayer upwards were formed by a potential cycling program, are reported. The multilayer oxide films were of the kind that exhibit reversible reduction/oxidation behavior. The kinetic experiments conducted in aq. at pH 2 give log [current] vs. overpotential relations having a constant Tafel slope of for all anode oxide surfaces prepared, indicating that the evolution mechanism is independent of the thickness of the oxide film produced. However, the apparent exchange current densities increase in an almost linear way with thickness. The latter behavior is attributed to an increase in the real area of the electrode available for Cl−discharge, coupled possibly with improved electrocatalysis, e.g., on account of changes that can arise in the band structure of the oxide. Increases of evolution rates of up to ca. 180× are found. Effects of Cl− adsorption on the development of the initial monolayer of oxide of Ir were also studied and compared with the behavior at Pt. Cl− adsorption is found to inhibit the formation of the thick oxide films at Ir.
81 citations
TL;DR: In this paper, the stochastic nature of the nucleation process was studied by analysing the induction times attending the birth of a single nucleus of mercury on a microscopic platinum electrode in an aqueous solution of mercurous ions.
56 citations
TL;DR: In this paper, the electrocatalytic performance of coal-derived hydrocarbons was investigated using a disc of scandia-stabilized zirconia (ZrO2) 0.92(Sc2O3)0.08, the anodic face of which was coated with porous platinum or gold as the electrode material.
Abstract: The electro-oxidation of those hydrocarbon fuels commonly derived from coal (e.g. CO, CH4 and H2) was studied using a disc of scandia-stabilized zirconia (ZrO2)0.92(Sc2O3)0.08, the anodic face of which was coated witheither porous platinumor gold as the electrode material. The cathode face of the disc was coated with porous platinum and exposed to air which provided the source of oxygen. The stabilizedzirconia reactor disc was operated at 700° C and 1 atmosphere in both the self-generated-power (fuel-cell) mode and the applied-power mode. From the experimentally observed behaviour of the current-overpotential curves the electrocatalytic oxidation of hydrocarbons is found qualitatively to be independent of whether porous gold or platinum is used at the anode. This behaviour indicates that the solid electrolyte itself is playing the major role in the electrocatalytic processes since platinum would be expected to be much more catalytic than gold in the electro-oxidation of these fuels. The fuel species investigated showed the following trend in the current drawn, and thus reactivity, at a given overpotential: H2>co>CH4.
33 citations
TL;DR: In this paper, the Tafel-Volmer route concluded previously of the hydrogen electrode on Pd has been substantiated and the effects of thiourea and tetrabutylammonium hydroxide upon the equivalent hydrogen pressure were examined and the results were interpreted in terms of their influences upon the rates of the elementary steps involved.
29 citations
TL;DR: In this article, the authors performed impedance measurements on rotating disk electrodes of La 0.5 Ba0.5 CoO 3 in 6 M KOH at room temperature and found that both the current and differential capacitance increase with increasing total dc passed.
25 citations
TL;DR: In this article, the kinetics of viologen cation radicals reacting at hydrogen-evolving gold and nickel electrodes in pH 6-8 electrolytes were investigated using visible absorption spectroscopy.
21 citations
TL;DR: In this article, a noble gas Au wire reference electrode was used to measure anodic and cathodic polarization during electrolysis, and steady state polarization curves were obtained at 800-1000 K with a matrix of fifteen mixtures.
Abstract: A molten carbonate electrolytic cell of the Broers and Ketalaar type was used to study the reactionin an Li/K carbonate eutectic melt with porous electrodes. A noble gas Au wire reference electrode was used to measure anodic and cathodic polarization during electrolysis. Steady‐state polarization curves were obtained at 800–1000 K with a matrix of fifteen mixtures: 0.5, 1, 10, 20, 50% , 19, 50% . Kinetic analysis in the linear overpotential region indicated is near zero for and 0.5 for . The kinetic Tafel slope was measured from current‐potential curves for current densities well below the diffusion limiting current and was found to be for cathodic polarization and for anodic polarization. The reaction orders are and in the cathodic direction, and and in the anodic direction.
17 citations
TL;DR: In this article, the electrochemical reduction of steam in a high temperature zirconia cell (i, e H2-H2O, Ni/YSZ/Pt, O2) is discussed and three types of measurements are reported: steady state U(I) plots, impedance spectroscopy analysis and Faraday efficiency determination.
01 Feb 1981
TL;DR: In this paper, the authors derived the interfacial concentration values derived from overpotential measurements on the cation exchange membrane AMF C 100 in relation to the corresponding currentvoltage curves.
Abstract: Interfacial concentration values derived from overpotential measurements on the cation exchange membrane AMF C 100 are considered in relation to the corresponding current-voltage curves. The concentration in the depleted layer was found to reach a limiting value as a function of current density which is still large compared to the H+ and OH− ion concentration. The pH shift and the cation transport number were also determined as a function of current density. It appeared that water splitting did not contribute significantly to the conductivity in the high polarization regime and could not be correlated with the constant value of the interfacial concentration nor with the additional conductivity which appears beyond the polarographic plateau.
TL;DR: In this article, the authors compare the data on the kinetics of electrode reactions of atomic hydrogen formed through capture by H 3 O + ions of electrons emitted into solution, compared with those on cathodic H 3O + ion discharge.
TL;DR: In this article, the effect of cadmium impurity in commercial zinc electrolytes on the zinc plating current efficiency in acid sulfate baths was investigated and the results indicated that the incorporation of the impurity into the zinc plate neither significantly alters the crystal orientation of the deposit nor alters the hydrogen evolution mechanism.
Abstract: A study was carried out on the effect of cadmium, a major impurity in commercial zinc electrolytes, on the zinc plating current efficiency in acid sulfate baths. The synthetic electrolyte (200 g dm−3 Zn++ and 0–100 mg dm−3Cd++) was continuously circulated through the electrolysis cell. The electrolysis was carried out with a current density of 480–490 A m−2 at 37°C. Hydrogen overpotential, potential sweep, atomic absorption, x‐ray diffraction, and electron microscopy were used to determine the effect of cadmium on the behavior of the zinc plate. The results indicate that cadmium may either increase or decrease the zinc plating current efficiency. For Cd++ less than 20 mg dm−3, increasing cadmium concentrations in the electrolyte reduce the hydrogen overpotential and the zinc plating current efficiency. For Cd++greater than 20 mg dm−3, increasing cadmium concentrations cause a refinement in the structure of the zinc plate with subsequent increase in the hydrogen overpotential and in the zinc plating current efficiency. The incorporation of cadmium into the zinc plate neither significantly alters the crystal orientation of the deposit nor alters the hydrogen evolution mechanism.
TL;DR: The overpotential of electrochemical reactions has a parallel in thermal reactions which may be called the overstress This quantity must be added algebraically to the free-energy change of reversible thermodynamics if one is to know the energy needed to carry out a reaction at a finite velocity or to find out the energy obtainable from a reaction occurring spontaneously as discussed by the authors.
TL;DR: In this paper, a search was conducted to find suitable additives to act as levelling agents in the electrodeposition of aluminium from a nonaqueous bath consisting of Al2Br6 and MBr in an aromatic hydrocarbon.
Abstract: A search was conducted to find suitable additives to act as levelling agents in the electrodeposition of aluminium from a nonaqueous bath consisting of Al2Br6 and MBr in an aromatic hydrocarbon. Two nitro-compounds were found to act effectively. The current-potential relationships were determined in the presence of different concentrations of these compounds in stirred and unstirred solutions and the effects observed were interpreted on the basis of a simple model. The increase of overpotential (at constant current density) with increasing mass transport rate was used as a qualitative criterion for the identification of an effective leveller.
TL;DR: In this article, the authors proposed a new general method which enables recombination kinetics to be tested over a full range of coverages and corresponding current densities, up to the saturation limiting value, by means of linear plots of a function in and exp.
Abstract: Hitherto, the criterion for recombination‐control in an electrochemical reaction sequence has been simply the observation of a Tafel slope of but applicable only to potential ranges where the coverage of the intermediate concerned is low (< ca. 15%). A new general method is proposed which enables recombination kinetics to be tested over a full range of coverages and corresponding current‐densities, up to the saturation limiting value, by means of linear plots of a function in and exp . If linear plots are found, both the recombination rate‐constant and the quasi‐equilibrium constant for the prior ion discharge/chemisorption step can be calculated. The method is illustrated by application to data for kinetics. The steepness of approach of overpotential vs. log [current] curves to the saturation limiting current is shown to be dependent on interaction effects in the ad‐layer, as seems to be indicated experimentally.
TL;DR: In this paper, the palladium-black-catalyzed electrogenerative hydrogenation of ethylene was investigated over partially wettable, porous, commercial electrodes between +0.6 and 0.3 atm partial pressure.
TL;DR: In this paper, a series of Ni electrodes were implanted at room temperature with various doses of 50 keV Ag +, Li +, He +, or Kr + ions, and polarization measurements were made in a suitable electrolysis cell over a wide range of current densities, using aqueous KOH solution (30%) at 80°C as electrolyte.
TL;DR: In this paper, the authors measured the conductivity of solid electrolytes having the composition RbCu 4 Cl 3+ x I 2− x where x = 0 or 0.25 were carried out using copper and Chevrel phase electrodes.
TL;DR: In this paper, the development of macromorphology of zinc deposits has been investigated under galvanostatic conditions on a rotating plantinum disk electrode by use of photomacrography, scanning electron microscopy, electron probe microanalysis and Auger microprobe analysis.
Abstract: The morphology of zinc as it is electrodeposited from acid solutions demonstrates a remarkable imprint of electrolyte flow conditions. The development of macromorphology of zinc deposits has been investigated under galvanostatic conditions on a rotating plantinum disk electrode by use of photomacrography, scanning electron microscopy, electron probe microanalysis and Auger microprobe analysis. Logarithmic spiral markings, which reflect the hydrodynamic flow on a rotating disk, appear in a certain region of current density well below the limiting current density. Morphological observations revealed the major influence of trace lead ions on the amplifications of surface roughness through coalescence and preferred growth of initial protrusions. Results obtained from ultra-pure electrolyte suggest preferred crystal growth towards well-mixed orientation in the concentration field caused by slight differences in crystallization overpotential. A qualitative model involving a coupling mechanism between the evolving surface roughness and instability phenomena in the boundary layer is advanced to explain the formation of spiral patterns.
TL;DR: In this article, the results of dc polarography and controlled potential chronoamperometry on a hanging mercury drop electrode were interpreted by assuming that the cathodic reduction of thorium on mercury proceeds through one step Th(IV)+4 e→Th(0) (E1/2⋍−1.65V vs. SCE in DMSO).
20 Sep 1981
TL;DR: In this article, the rate of metal corrosion with hydrogen depolarization is determined by the kinetics of cathodic evolution of hydrogen, and the decrease of the electrode reaction in presence of inhibitors is caused mainly by partial blocking of the metal surface, and production of an adsorption psi/sub 1/ potential.
Abstract: The rate of metal corrosion with hydrogen depolarization is determined by the kinetics of cathodic evolution of hydrogen. It was shown earlier in a study of the influence of organic inhibitors on the overpotential n of cathodic evolution of hydrogen on iron that, depending on the adsorbability of the additives, not only the rate but also the mechanism of the cathode process varies. The decrease of the rate of the electrode reaction in presence of inhibitors is caused mainly by two factors: partial blocking of the metal surface, and production of an adsorption psi/sub 1/ potential. With assumption of linear variation of the psi/sub 1/ potential with increasing degree of surface coverage THETA of the electrode surface by the organic additive leads to the following expression for the retardation coefficient: ..gamma..=i/i/sub base/ =1//sub 1-THETA/exp(kTHETA), where i and i/sub base/ are the reaction rates in presence and absence (in the base electrolyte) of the inhibitor, and k is a proportionality factor.
TL;DR: In this paper, the open-circuit potential in H2-saturated electrolytes, and the kinetics of hydrogen reactions, in particular of hydrogen evolution reaction, on smooth, rotating disc tungsten carbide WC electrode have been investigated, in 0.5 M sulfate solutions of pH 0.3 and 1.85, in the temperature range 30 to 80°C.
Abstract: The open-circuit potential in H2-saturated electrolytes, and the kinetics of hydrogen reactions, in particular of hydrogen evolution reaction, on smooth, rotating disc tungsten carbide WC electrode have been investigated, in 0.5 M sulfate solutions of pH 0.3 and 1.85, in the temperature range 30 to 80°C. Anodically activated electrodes were used too. It was proved that values of the open-circuit potential in the near vicinity of reversible hydrogen electrode potential can be observed, under condition of high purity, and of tight mounting of the sample in the electrode holder. Two Tafel regions have been observed for hydrogen evolution reaction, both the Tafel slopes having no systematic variation with temperature. In the lower overpotential region the experimental charge transfer coefficient attained the value of 1, when the temperature was increased up to 80°C. It was suggested that the process approached the barrierless form when the temperature was increased. The mechanism of hydrogen reactions on WC was discussed. It was suggested that the rate of the process is possibly determined by the rates of its two steps simultaneously. The role of pH on the activation process of WC was emphasized, and implications of the hydrogen evolution reaction parameters on the mechanism of this process were pointed out.
TL;DR: The potential dependence of the combined nucleation and crystallization rate constants was found to be [7.8 ± 0.7 mV/decade]−1.
Abstract: The electrochemical oxidation of Pb(Hg) in acidic phosphate medium results in formation of a monomolecular PbHPO4 passivating film. Analysis of potentiostatic current-time transients demonstrated that the crystallization occurred through a 2-dimensional progressive nucleation and growth mechanism. The potential dependence of the combined nucleation and crystallization rate constants was [7.8 ± 0.7 mV/decade]−1. The formation of a soluble lead phosphate species prior to film growth was observed under certain conditions. Examination of it curves in this region by the low overpotential form of the Cottrell equation indicated that the soluble species was PbHPO4.
TL;DR: In this article, the initial electrocatalytic activity for oxygen evolution in acid electrolyte was determined using the potentiostatic method, and the surface areas of these oxides were estimated using cyclic voltammetry.
Abstract: Ruthenium oxide, prepared by the thermal decomposition method, has the highest known initial electrocatalytic activity for oxygen evolution in acid electrolyte. However, this material is not stable in the electrolyte and at the same time exhibits a significant increase of oxygen overpotential with time, probably due to a chemical transformation of the oxide from a lower to a higher valence state. Efforts were made to stabilize ruthenium by preparing mixed oxides with Ir and/or Ta using the thermal decomposition method. The electrocatalytic activities for oxygen evolution on these oxides in were determined using the potentiostatic method. The surface areas of these oxides were estimated using cyclic voltammetry. Dual Tafel slopes (approximately 30 and 40 mV) were found on most of these oxides. The ternary oxide exhibited a single Tafel slope of 30 mV, had the lowest overpotential, and showed minimum variation of overpotential with time.