Abstract
Summaryo1.Of the systems studied, the indium/sodium sulphate system is the only one to show potential regions where the electrode-aqueous solution interphase is considered to be uncomplicated by adsorption or the intrusion of films. An estimate of the p.z.c. for this system is −0.95±0.02 V.2.It is not possible to determine unequivocally the p.z.c. for indium in fluoride electrolytes, although a well-defined capacitance minimum occurs at −0.93±0.02 V in dilute fluoride solutions.3.For unacidified chloride and perchlorate electrolytes a well-defined capacitance minimum is not observed as the ionic concentration is lowered.4.In unacidified solutions of KF and NaClO4 at high ionic concentrations, the anodic rise in electrode capacitance due to lattice oxidation is suppressed, due to the irreversible formation of highly insoluble films at the electrode surface.5.A pseudocapacitance peak at −0.90 V in KF solutions, −0.90 V in NaClO4 solutions and −0.95 V in KCl solutions is concluded as being due to OH− ion interaction with the indium electrode surface and subsequent dissolution of the metal lattice. Of the systems studied, the indium/sodium sulphate system is the only one to show potential regions where the electrode-aqueous solution interphase is considered to be uncomplicated by adsorption or the intrusion of films. An estimate of the p.z.c. for this system is −0.95±0.02 V. It is not possible to determine unequivocally the p.z.c. for indium in fluoride electrolytes, although a well-defined capacitance minimum occurs at −0.93±0.02 V in dilute fluoride solutions. For unacidified chloride and perchlorate electrolytes a well-defined capacitance minimum is not observed as the ionic concentration is lowered. In unacidified solutions of KF and NaClO4 at high ionic concentrations, the anodic rise in electrode capacitance due to lattice oxidation is suppressed, due to the irreversible formation of highly insoluble films at the electrode surface. A pseudocapacitance peak at −0.90 V in KF solutions, −0.90 V in NaClO4 solutions and −0.95 V in KCl solutions is concluded as being due to OH− ion interaction with the indium electrode surface and subsequent dissolution of the metal lattice. The concentration of solution soluble indium species in equilibrium with the electrode at the capacitance peak has been calculated for the fluoride and chloride cases (1 mol l−1, unacidified solutions) at these peak potentials.
Published Version
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