Showing papers on "Overpotential published in 1976"

Study of the effectiveness of fixed flow-through electrodes

Abstract: This paper presents a theoretical and experimental study of the effectiveness of fixed flow-through electrodes working at very low local overpotentials. An analogy is established between such systems and gas-solid catalytic reactors; a generalisation which extends the treatment to high overpotential operating conditions is also presented. The study establishes the pertinent parameters of the electrode and outlines the conditions for its 3-dimensional behaviour.

Mathematical model and digital simulation of pulsating overpotential copper electrodeposition

Abstract: The relationships between the effective current density and the effective overpotential in copper electrodeposition carried out by pulsating overpotential have been analysed experimentally and by digital simulation on the basis of a simple mathematical model. The agreement between the theoretical and experimental results was satisfactory. The quality of the electrodeposit was also studied.

Electric storage battery with valve metal electrodes

Abstract: Electric storage batteries with titanium or other film forming metal anodes and cathodes are provided. The anodes are coated with mixed oxide coatings of a film forming metal oxide containing a platinum group metal oxide catalyst, which coatings may contain oxides of other metals to alter the breakdown voltage and increase the oxygen overpotential of the cathodes while preserving a low bromine and chlorine overpotential. The cathodes may be uncoated titanium or other film forming metals or film forming metals with a silver coating thereon. Bipolar film forming metal cathodes and anodes are provided carrying a mixed oxide coating on the cathodic face and either no coating or a silver coating on the anodic face. The invention is applicable to all types of electric storage batteries, either primary or secondary, and multiple batteries may be connected in series or in parallel to provide the desired amperage and voltage characteristics.

Calculations on the effect of gas evolution on the current-overpotential relation and current distribution in electrolytic cells

Abstract: Gas evolution during electrode reactions has several effects on the electrode behaviour. One of these effects is the nonuniform increase of the resistivity of the electrolyte with the resultant increase of IR drop through the solution and the distortion of current distribution. Calculations of these effects are presented for an electrode built of vertical blades. This geometry has the peculiarity that it allows the inclusion of linear polarization and gas effects in the treatment, without the necessity to use numerical or approximate solutions of the differential equations. It is shown that the system parameters can be combined into a single dimensionless parameter to describe those aspects of the electrode behaviour which depend on the gas evolution. The parameters examined include the geometry of the electrode, the polarization resistance, gas bubble rise velocity, and solution resistivity. Expressions are given for optimization of the electrode geometry to achieve minimum overpotential.

The mechanism of formation of a surface film of silver on a platinum electrode

Abstract: The mechanism of the growth of thin metal films on inert substrates in potentiostatic metal electrodeposition is given. A possible relation to the porosity of metal deposits is discussed. The effects of pulsating overpotential on the electrodepositon of the first monolayers are described.

Microstructural aspects of grid corrosion in the PbO/sub 2/ electrode

Abstract: A radical change in microstructure was examined for its effect on the mode of corrosive attack and corrosion rate for a 5 weight percent antimonial lead alloy. Metallography on as-cast microstructures indicates a transition from interdendritic to general attack with increasing overpotential. The potential region for general attack corresponds to a breakdown in the passivating abilities of PbO/sub 2/, and is marked by a sharp rise in the corrosion current. A simple heat-treatment, which alters the structure of the eutectic material, reduces interdendritic attack over the entire potential region studied. 8 figures, 2 tables.

Elementary reaction rates of the hydrogen electrode reaction on nickel analyzed by means of deuterium tracer. i. the anodic region

Abstract: The exchange reaction between deuterium gas and light water was conducted with a nickel electrode under anodic polarization. The rates of the constituent steps of the hydrogen electrode reaction were determined at various anodic overpotentials through analysis of the isotropic composition of the hydrogen gas. Reaction route (B  H 2 O, or OH − ) was shown to interpret satifactorily the results. The former step is rate-determining under low hydrogen pressures, whereas the latter becomes kinetically important at high hydrogen pressures. Dependence of the individual step rates upon overpotential was discussed.

Cyclic voltammetry of monel 400 in lithium hydroxide solution at elevated temperatures

Abstract: The electrochemistry of Monel 400 in 1 mole/kg −1 LiOH solution at 25, 125 and 250°C has been investigated using the technique of cyclic voltammetry. The general electrochemical behaviour is found to most closely approximate to that of the major component, nickel, although expansion of the current scale reveals anodic and cathodic peaks which probably arise from redox processes involving copper. The general similarity to nickel can be rationalized in terms of either the d electron theory for cupronickel alloys or phase separation, the latter being favoured in the present study. At 25°C the majority of charge consumed on sweeping the potential in the positive direction is involved in the formation of an oxide film at potentials close to oxygen evolution. This process is no longer observed at 250°C, due to a sharp reduction in the oxygen evolution overpotential with temperature. The majority of charge consumed on cyclic sweeping at this temperature is attributed to active dissolution of the nickel component of the alloy to form HNiO − 2 (or Ni(OH) − 2 (or Ni(OH) − 3 ) at potentials slightly positive to the hydrogen evolution region.

Measurement of Fluxes and Forces at the Surface of Cation Exchange Membranes under Conditions of Controlled Polarization

Abstract: Methods for the measurement of fluxes and forces at the interfaces of a cation-exchange membrane in dilute (01 M) sodium chloride have been developed Instead of neglecting or eliminat­ing inasfar as possible both polarization layers, one of them was stabilized and expanded by the use of a contiguous agarose gel film This method makes for a high level of uniformity over the interface and affords easy control of concentration profiles Consequently, a well-defined polarographic plateau is observed in current-voltage data From determinations of the relaxation time of the overpotential, one can calculate both the interfacial concentrations and the forces which prevail, namely, the potential ΔE between the two membrane interfaces Volume flows were measured in the conventional manner but new methods were employed to measure the ionic fluxes All of this methodology allows one to obtain directly the nine coupling coefficients of the membrane without resort to pressure measurements as shown in the second part of this contribution