Abstract
We examined the electroreduction of Bi (III) ions in chlorate (VII) solutions under varied protonation conditions of the depolariser using voltammetric and impedance methods. The results of the kinetic parameter correlation lead to the statement that the changes in the amount of chloric (VII) acid against the amount of its sodium salt in the supporting electrolytes of the low water activity have a significant influence on the rate of Bi (III) ion electroreduction. The increase of the concentration of chloric acid sodium salt, as well as the chloric (VII) acid alone within the particular concentration of the supporting electrolyte, inhibits the process of Bi (III) ion electroreduction. It should be associated with the reorganisation of the structure of the double layer connected with the slow dehydration inhibited by ClO 4− ions. The standard rate constants ks values with the increase of the chlorate (VII) concentrations for all the solutions examined of chlorates (VII) confirms the catalytic influence of the decrease of water activity on the process of Bi (III) ion electroreduction. The multistage process is confirmed by the non-rectilinear 1nkf = f(E) dependences.
Highlights
The electrochemical properties of metal ions depend on the composition and concentration of the supporting electrolyte.The metal cations in aqueous solutions show strong interactions with water molecules
It suggests that the composition of the active complex is independent on the concentration ratio HClO4 and NaClO4; whereas the peaks’ height is practically unchanged with the change of chlorates (VII) concentration, which points to the fact that in the solutions with a large excess of chloric (VII) acid in comparison with sodium chlorate (VII), the rate of Bi (III) ion electroreduction is practically independent from the chlorate (VII) concentration
In the solutions with the preponderant concentration of chloric (VII) acid in the supporting electrolyte solution (6D, 6E), the shift of the cathodic peaks potentials towards more negative potentials is observed, whereas the anodic peaks are shifted towards the more positive potentials. Such oscillations of the cathodic and anodic peaks potentials in the function of the changes of NaClO4 and HClO4 concentration ratios in the supporting electrolyte suggest the differences in the mechanism of Bi (III) ions electroreduction, as well as the significant dependence of the active complex structure on the composition of the supporting electrolyte [3, 4]
Summary
The electrochemical properties of metal ions depend on the composition and concentration of the supporting electrolyte.The metal cations in aqueous solutions show strong interactions with water molecules. The standard rate constants ks values with the increase of the chlorate (VII) concentrations for all the solutions examined of chlorates (VII) confirms the catalytic influence of the decrease of water activity on the process of Bi (III) ion electroreduction.
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