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Showing papers on "Overpotential published in 1977"


Journal ArticleDOI
TL;DR: In this article, the behavior of semiconducting electrodes for photoelectrolysis of water is examined in terms of the physical properties of the semiconductor and the photocurrent is described using a simple Schottky barrier.
Abstract: The behavior of semiconducting electrodes for photoelectrolysis of water is examined in terms of the physical properties of the semiconductor. The semiconductor‐electrolyte junction is treated as a simple Schottky barrier, and the photocurrent is described using this model. The approach is appropriate since large‐band‐gap semiconductors have an intrinsic oxygen overpotential which removes the electrode reaction kinetics as the rate‐limiting step. The model is successful in describing the wavelength and potential dependence of the photocurrent in WO3 and allows a determination of the band gap, optical absorption depth, minority‐carrier diffusion length, flat‐band potential, and the nature of the fundamental optical transition (direct or indirect). It is shown for WO3 that minority‐carrier diffusion plays a limited role in determining the photoresponse of the semiconductor‐electrolyte junction. There are indications that the diffusion length in this low carrier mobility material is determined by diffusion‐controlled bulk recombination processes rather than the more common trap‐limited recombination. It is also shown that the fundamental optical transition is indirect and that the band‐gap energy depends relatively strongly on applied potential and electrolyte. This effect seems to be the result of field‐induced crystallographic distortions in antiferroelectric WO3.

1,758 citations


Journal ArticleDOI
TL;DR: In this paper, the small-signal steady-state response around the point of zero charge of an electrode/material system is examined for an unsupported electrolyte (material) with two species of charge carrier of arbitrary mobilities and valence numbers and with arbitrary intrinsic/extrinsic conduction character, taking full account of bulk, electrode reaction, sequential adsorption, and diffusion processes.

115 citations


Journal ArticleDOI
TL;DR: In this article, the authors deal with an experimental study of copper deposition in fluidized bed electrodes from acidified aqueous solutions containing copper and determine overpotential distributions and the amount of copper deposited at various levels within the electrodes.
Abstract: This paper deals with an experimental study of copper deposition in fluidized bed electrodes from acidified aqueous solutions containing copper. Overpotential distributions are determined and the amount of copper deposited at various levels within the electrodes is also measured. Experiments with long duration times allow the variations of current efficiency for recovery to be obtained as a function of current density and fixed bed thickness. These variations could be explained by the existence of dissolution zones within the electrodes.

42 citations


Journal ArticleDOI
TL;DR: In this paper, theoretical equations were developed to represent the overpotential decay behavior of a polarized electrode following current interruption in the course of a faradaic reaction, and three mechanistic schemes were considered: (a) fast discharge, slow recombination and/or slow electrochemical desorption; (b) slow discharge, fast recombination of fast electrochemical degradations; (c) Coupled discharge, electrochemical disorption or recombination).

39 citations


Journal ArticleDOI
TL;DR: In this article, the structure of the two-dimensional layers formed in the underpotential deposition of lead onto carefully prepared single crystals of copper are shown to depend upon the substrate orientation for (111), (100) and (110) surfaces.
Abstract: The structures of the two-dimensional layers formed in the underpotential deposition of lead onto carefully prepared single crystals of copper are shown to depend upon the substrate orientation for (111), (100) and (110) surfaces. Nucleative growth processes are observed for first order and for higher order phase transitions. Comparison is made with the behaviour observed on silver substrates and the differences are ascribed to the change in atomic radius and in eletronegativity. Formation of the underpotential layer is shown to be a necessary precursor to overpotential deposition, the mechanism of which is markedly dependent on substrate orientation.

35 citations


Patent
27 Jul 1977
TL;DR: In this paper, an active metal coating which lowers the hydrogen discharge overpotential at the cathode in the electrolysis of aqueous alkali metal halide solutions is deposited on the cathodes tubes of a cathode can of an electrolysis cell without the removal of the tubes from the can.
Abstract: An active metal coating which lowers the hydrogen discharge overpotential at the cathode in the electrolysis of aqueous alkali metal halide solutions is deposited on the cathode tubes of a cathode can of an electrolysis cell without the removal of the tubes from the can. Plating solution and anodes of plating metal are placed inside a cathode can and the components are electrically connected so as to deposit an active coating onto the cathode tubes. The plating metal is preferably an alloy of nickel and zinc and the process involves the final step of leaching the zinc component of the alloy deposit from the plated cathode tubes to provide a porous, active nickel surface which results in a reduction of the hydrogen discharge overpotential for the electrolysis of alkali metal halides, particularly sodium chloride.

28 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the ohmic resistance, the equilibrium potential, the charge-transfer overpotential and the diffusion polarization of the working cell in a working cell with and without organic nitriles.
Abstract: Organic nitriles stabilize acidic aqueous copper(I) sulphate solutions. Electrolysis of such solutions provides an alternative for the electrowinning and electrorefining of copper. The Cu+/CuO and Cu2+/Cu+ standard reduction potentials in aqueous solutions containing acetonitrile or 3-hydroxy-propanenitrile (hydracrylonitrile) differ from those in water, due to the specific solvation and stabilization of the copper(I) ion by either nitrile. In the mixed solvent, the solvation sphere around the copper(I) ion contains organic nitrile, rather than water, and this reduces the mobility of Cu+ and slows its diffusion to the electrode surface in a working cell. The copper(II) ion contains water in its solvation shell in the mixed solvent. Thus for dilute solutions, the diffusion coefficient of the copper(I) ion in 10 mole % aqueous acetonitrile is about two-thirds and in 10% 3- hydroxypropane-nitrile-water is about one-fifth that of the copper(II) ion in water. In concentrated solutions containing sulphuric acid, the copper(II) ion diffuses as ion pairs and this reduces its mobility. This effect is not observed for copper(I) ions. Cell voltages measured during the electrolysis of copper(I) sulphate solutions by using soluble copper, insoluble platinum or insoluble carbon anodes are analysed in terms of the ohmic resistance, the equilibrium potential, the charge-transfer overpotential and the diffusion polarization of the working cell. There is a significant charge-transfer overpotential for the oxidation of Cu+ to Cu2+ at an insoluble graphite anode in 6 mol dm-3 acetonitrile-water solutions; the rate constant is 4 x 10-4 cm s-1. At platinum the rate constant is 1.6 x 10-2 cm s-1.

25 citations


Journal ArticleDOI
TL;DR: In this paper, the possibility of electrodepositing copper powder by pulsating overpotential was shown, and it was shown that the grain size and the morphology of deposited powder is a function of overpotentials, and of amplitude and frequency of pulsation in constant and pulsatingoverpotential deposition respectively.
Abstract: The possibility of electrodepositing copper powder by pulsating overpotential is shown. These powders are compared to the powders obtained by constant overpotential electrodeposition. It is also shown that the grain size and the morphology of deposited powder is a function of overpotential, and of amplitude and frequency of pulsation in constant and pulsating overpotential deposition respectively.

19 citations


Patent
11 Jul 1977
TL;DR: An active coating comprised of a mixture of palladium oxide and zirconium dioxide on a metal substrate selected from a group consisting of iron, nickel, cobalt and alloys thereof, results in a lower hydrogen overpotential at the cathode in the electrolysis of aqueous alkali metal halide solutions.
Abstract: An active coating comprised of a mixture of palladium oxide and zirconium dioxide deposited on a metal substrate selected from a group consisting of iron, nickel, cobalt and alloys thereof, results in a lower hydrogen overpotential at the cathode in the electrolysis of aqueous alkali metal halide solutions. Salts of the component metals of the coating are deposited on the cathode surface preferably by painting. The coating metals are then converted to the corresponding metal oxides through the heating of the coating and substrate to 300° to 600° C in an oxidizing atmosphere such as air or oxygen. The coating results in a lowering of the hydrogen discharge overpotential at the cathode surface of about 50 to 100 millivolts as compared with the hydrogen discharge overpotential for the mild steel substrate commonly used as a cathode in electrolysis cells.

18 citations


Journal ArticleDOI
TL;DR: In this paper, a number of observations on the electrooxidation of lead in 5M H/sub 2/SO/sub 4/ are presented, and it is shown that the induction period in the potentiostatic oxidation to lead is due to the thickening of the PbSO/Sub 4/ film and that a rising current transient signals the development of phase PbO/Sub 2/; the minimum overpotential for this is approx. 200 mV.
Abstract: A number of observations on the electrooxidation of lead in 5M H/sub 2/SO/sub 4/ are presented. It is shown that the induction period in the potentiostatic oxidation to PbO/sub 2/ is due to the thickening of the PbSO/sub 4/ film and that a rising current transient signals the development of phase PbO/sub 2/; the minimum overpotential for this is approx. 200 mV. On a Pb--PbO/sub 2/PbSO/sub 4/ electrode a rising current response to a potentiostatic experiment is not generally obtained due to the presence of adequate growth centers. Battery behavior is in agreement with the observations. 8 figures.

15 citations


Journal ArticleDOI
TL;DR: In this paper, the particle grain size and the morphology of deposited powders were shown to be functions of amplitude overpotential, frequency of pulsation and pulse to pause ratio in pulsating potential deposition, and of overpot potential in constant over-potential deposition.
Abstract: Copper powder deposits were obtained by square-wave pulsating overpotential electrolysis and by constant overpotential electrolysis. It is shown that the particle grain size and the morphology of deposited powders are functions of amplitude overpotential, frequency of pulsation and pulse to pause ratio in pulsating potential deposition, and of overpotential in constant overpotential deposition.

Journal ArticleDOI
TL;DR: In this article, the experimental determination of the effect of ohmic overpotential on the transient response of a three-dimensional progressive nucleation and growth mechanism is described and the experimental data are shown to agree with theoretical predictions.

Journal ArticleDOI
TL;DR: In this article, a computer simulation of the voltammogram corresponding to the two dimensional progessive nucleation and growth of a passivating film is presented, and the effect of varying parameters is discussed in terms of the peak potential and peak current.

Journal ArticleDOI
TL;DR: The porosity of copper deposits on steel obtained by constant and pulsating overpotential electrolysis has been investigated and determined as a function of the over-potential of deposition as mentioned in this paper.
Abstract: The porosity of copper deposits on steel obtained by constant and pulsating overpotential electrolysis has been investigated and determined as a function of the overpotential of deposition. Optimal conditions for copper plating on steel from pyrophosphate baths have been established.

Journal ArticleDOI
TL;DR: In this paper, the potential sweep diagrams were characterized by a loop exhibiting an inductive nature and two maxima on the anodic branch of the voltammogram could be attributed to the dissolution of non-epitaxial and epitaxial deposits.

Journal ArticleDOI
TL;DR: In this article, the results obtained with KCl and HCl solutions on cation membranes with the current interruption technique are analyzed and a consistent influence of competitive H+ transport in KCl solutions in high polarization conditions is found while in HCl solution Nernst-Plank equations hold for interfacial concentrations as low as 10-7N.

Patent
11 Aug 1977
TL;DR: In this paper, a combination of a cation exchange diaphragm and a porous metal cathode of low H overpotential is used to produce chlorine and caustic alkalies.
Abstract: Chlorine and caustic alkalies are produced by an electrolytic dissociation of alkali chloride and with the evolution of H gas, by using a combination of (a) a cation exchange diaphragm and (b) a porous metal cathode of low H overpotential which is located next to the diaphragm and the anode. The anode chamber, separated by the diaphragm from the cathode chamber is filled with an aq. soln. contg. 20-27 wt. % NaCl held a temp. 60-90 degrees C, and the cathode chamber is filled with an aq. NaOH soln., the concn. of which is maintained at 25-50 wt. % (20-45 wt. %) NaOH by replacing drained cuastic alkali soln. by water, and held at a temp. 60-90 degrees C. The cell is operated by using a direct current of c.d. 0.54-5.4 Ka/m2 (1.07-4.28 kA/m2) through an anode of stable dimension in the anode chamber, a Raney nickel electrode in the cathode chamber and fed through the soln. via the diaphragm between the anode and cathode, which is composed of a polymer of perfluorsulphonic acid-poly-fluorhydrocarbon. Bubble formation between the electrodes is minimised so that the electrodes with the diaphragm between can be located close to each other. Pollution problems are greatly reduced as no Hg is used in the construction of the cells.

Patent
07 Jul 1977
TL;DR: In this paper, a textured surface of lead dioxide was electrodeposited in such a manner to produce a multiplicity of upwardly protruding platelets for solar energy collector surface, the effectiveness as a collector is relatively independent of incident angle.
Abstract: Solar energy collector surface, the effectiveness of which as a collector is relatively independent of incident angle, comprises a textured surface of lead dioxide electrodeposited in such a manner to produce a multiplicity of upwardly protruding platelets. The electrodeposition technique comprises an initial nucleation stage in which a relatively high overpotential is applied for a short period of time and a subsequent oriented growth stage in which a lower overpotential is applied for a longer period of time than in the first stage.

Journal ArticleDOI
TL;DR: In this paper, a galvanostatic transient technique was used to separate interfacial overpotential from bulk resistivity effects for Na + ion transport between polycrystalline beta alumina and propylene carbonate.

Journal Article
TL;DR: In this paper, the distribution of reaction affinity among constituent steps of the hydrogen electrode reaction and the current 1'S. The surface coverage term does not much influence the affinity distribution but the current vs. overpotential relations are significantly modified.
Abstract: Analysis of the distribution of the reaction affinity among constituent steps of the hydrogen electrode reaction and the current 1'S. overpotential relation, reported previously, was extended taking the impeding effect of the surface coverage into consideration. The discharge-combination and the discharge-electrochemical desorption routes were treated assuming the LANGMUIR and FRUMKIN-TEMKIN adsorption isotherms for the reaction intermediate. The surface coverage term does not much influence the affinity distribution but the current vs. overpotential relations are significantly modified. Comparison with experiments on Ni and Rh suggests that the kinetically effective surface coverage of the hydrogen intermediate would be much smaller than that observed electrochemically.

Journal ArticleDOI
P.L. Bonora1
TL;DR: In this paper, the electrochemical behavior of three Al-Zn alloys (1 − 5 - 10% Zn) in 0.5 NaCl solutions with a pH of 2 and of 8.2, under controlled fluid dynamic conditions (rotating disks at 500 − 2500 rp.m.) at 20 − 40 - 60°C has been studied.

Patent
25 Nov 1977
TL;DR: In this article, a self-supporting matrix consisting of an oxy cpd of actinides and lanthanides was used for the electrolytic prodn, which has a conductivity comparable to graphite, high chemical stability, good sintering properties and workability.
Abstract: Electrode for an electrolysis cell comprises a sintered self-supporting matrix consisting of an oxy cpd.(s) of Ti, Ta, Zr, V, Nb, Hf, Al, Si, Sn, Cr, Mo, W, Pb, Mn, Be, Fe, Co, Ni, Pt, Pd, Os, Ir, Re, Tc, Rh, Ru, Au, Ag, Cd, Cu, Zn, Ge, As, Sb, Bi, B, Sc, actinides and lanthanides, with addition of a minor proportion of an electro-conductive component (ZrO2, SnO2, Y, Cr, Mo, Zr, Ta, W, Co, Ni, Pd and/or Ag.). At least a part of the surface acting as an anode carries an electrocatalyst (an oxide(s) of Co, Ni, Mn, Rh, Ir, Ru and/or Ag.). The electrode has a conductivity comparable to graphite, high chemical stability, good sintering properties and workability. It can be used for the electrolytic prodn. of metals from fused salts (e.g. halides of Al, Mg, Na, K, Ca, Li, etc.). The electrocatalyst lowers the overpotential of the electrode.

Journal ArticleDOI
TL;DR: In this paper, it has been argued that the electrode kinetics are determined by reaction at the layer/solution interface, at relatively low c.d., the rate determining step is more likely the diffusion of Sn2+ through the layer, contributing appreciably higher over-potentials.


Journal ArticleDOI
TL;DR: In this article, an unambiguous definition of the different overpotential terms is possible based on the theory of non-equilibrium thermodynamics, which is a direct consequence of the thermodynamic irreversibility of the processes taking place in an electrochemical system, and the irreversible entropy production of a process occurring at a finite rate.