Significance of e.m.f. decay measurements. Applications to the nickel oxide electrode

Abstract

The significance of observations of rates of e.m.f.-decay on opencircuit at the nickel oxide electrode is examined in terms of the potential dependefice of the surface capacitance associated with the processes occurring during decay. Results are compared with those reported by Lukovtsev and Temerin and it is concluded that a capacity based on the properties of the surface layer (e.g., adsorbed oxygen radicals or a highly oxidized nickel oxide surface phase) must be used rather than one based on the oxidation-reduction behaviour of the bulk phase oxide. Direct micro-volumetric determinations of volumes of oxygen evolved from the electrode during opencircuit e.m.f.-decay allow quantitative comparisons to be made between true Tafel slopes and open-circuit e.m.f.-decay slopes. These slopes are shown to be identical only when the volume of oxygen evolved from the surface is a linear function of e.m.f. When the e.m.f. is a logarithmic function of the oxygen evolved, Tafel and decay slopes are shown to differ in the theoretically expected direction. The linear and logarithmic behaviour with respect to e.m.f. and volumes of oxygen evolved can be shown to follow as limiting conditions of the adsorption behaviour of oxygen at the electrode surface, depending upon the extent of surface coverage. The kinetic significance of the surface capacitance is discussed in relation to the e.m.f. decay behaviour. 593* This is based on a figure of 50 mA per actual plaque used (7-5 x 2 5 x 0.1 cm in size).* Very recent work by Conway and Gileadi indicates that when the true reversible potentials (as distinct from mixed potentials 2) are deduced, the Nernst redox slope for the bulk material is, in fact insignificantly merent from zero within the experimental error of f 5 mV.

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

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Hydrous Nickel Oxide: Redox Switching and the Oxygen Evolution Reaction in Aqueous Alkaline Solution

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The Oxygen Evolution Reaction at Manganese Oxide Films in Base: Kinetics and Mechanism

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