On the impedance of galvanic cells XXIV. The impedance of the In3+/In(Hg) electrode reaction in KSCN and KCl solution

Abstract

The In3+/In(Hg) system in KSCN and KCl solutions has been investigated using both d.c. and a.c. measurements. The experimental data are analysed and interpreted according to theoretical equations presented recently.

It is shown that the specific adsorption of indium from 1 M KSCN follows a linear adsorption isotherm up to 0.4 mM. No specific adsorption of indium can be detected from KCl solutions. The electrode reaction in 1 M KCl is not complelely reversible: ksh=(6±2)·10−2 cm/sec at the standard potential, supporting the hypothesis that adsorption of reactants renders an electrode reaction reversible.

Also, the minima in the In3+ limiting current have been studied. It appears that the faradaic impedance is negative at the potentials of the minimum. The phenomena are explained qualitatively with equations based on a potential-dependent ksh. Some arguments are presented for this potential-dependency; it is proposed that ksh depends exponentially on the specifically adsorbed charge, q1, of the anions of the supporting electrolyte. The exponential dependence of ksh on q1 was verified for 0.4 mM In3+ in 1 M KCl at potentials near the half-wave potential.