Piotr Piela

Oxidation of Nitrite on Solid Electrodes II. Determination of the Reaction Mechanism on Surfaces Covered by an Oxide Layer

The nitrite oxidation process was reinvestigated at rotating gold and platinum electrodes covered by an oxide layer. The electrochemical properties of the surface oxides were determined by recording the coverage curves of the gold and platinum electrodes at various pH values and for different experiment durations. The reaction mechanism on the oxidized surface was found to be the same as that on the oxide-free surface. The sole effect of the surface oxide was a drop of the standard rate constant of the electrode reaction which was a function of the surface coverage by the oxide. Nitrite oxidation on the oxide-covered electrodes was found to proceed via the innersphere mechanism with inhibitor adsorption on an energetically uniform surface. The kinetic results obtained for the gold and the platinum electrode were almost the same. The complicated shape of rotating disk voltammograms was explained in terms of the increase of the rate of the electrode reaction with increasing electrode potential and the drop of the standard rate constant of the electrode reaction with increasing electrode potential due to the increase of the oxide coverage with electrode potential, the latter process being dependent on the electrode material, pH, and time (scan rate).

The role of water and temperature in the electrochemical behavior of solid iron(III) hexacyanoferrate(II/III)

Abstract The influence of temperature over the range from −30 to 25°C on the electrochemical properties of solid iron(III) hexacyanoferrate(II/III) containing various amounts of water has been studied by means of cyclic voltammetry and impedance spectroscopy. The system studied is a water-insoluble mixed-valence coordination compound. The experiments have shown in major role for water molecules in the charge transport across this solid system. An attempt has been made to understand the experimental data on the basis of an existing model of redox conductance in solid mixed-valence transition metal hexacyanoferrates. The activation energy of charge migration in a partially dehydrated system and the activation energy of charge diffusion in a well-hydrated system have been determined.