The Reduction of Indium(III) in Thiocyanate Solutions at the Dropping Mercury Electrode

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Abstract
The reduction process of indium(III) at the dropping mercury electrode in thiocyanate solutions has been investigated by direct current polarography, alternating current polaro-graphy and faradaic impedance measurements. The reduction current in the potential region between −0.5 to −0.9 V. vs. saturated calomel electrode is greatly increased by the addition of minute amounts of thiocyanate ions, when a remarkable minimum is observed on the diffusion current plateau at relatively negative potentials. On the alternating current polarogram, indium(III) in a potassium thiocyanate solution gives a negative admittance in the potential region where the minimum appears on the direct current polorogram. The analysis of impedance measurements has shown that the resistance component has a negative value in that potential region. The experimental results have been explained by assuming that the overall electrode process is composed of two simultaneous reactions, one of which proceeds at the naked electrode surface, and the other at the electrode surface covered with adsorbed thiocyanate ions, and by assuming that thiocyanate ions accelerate the reduction of indium (III) at the surface of the electrode.

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