The electrochemistry of the tin oxide semiconductor—I. the establishment of mechanisms at polarized n-type tin oxide

Abstract

The mechanisms of electrode potential re-establishment of the n-type unstoichiometrical tin oxide semiconductor electrode after cathodic and anodic polarization was investigated. The tin oxide semiconductor was polarized cathodically and anodically without evolution of hydrogen or oxygen and the potential/time curves at open circuit were observed. After cathodic polarization, the potential/time curve had one wave. The potential of this wave depended on the concentration and nature of the electrolytes, while its life-time depended on the imposed electrode charge. After anodic polarization, the potential/time curves did not show a similar wave.This behaviour is interpreted as follows: Sn—O—H bonds are formed on a SnO2 lattice during cathodic polarization by the reduction of adsorbed H+ ions and H2O. The Sn—O—H formed on the semiconductor surface decomposes through an electron transfer process at open circuit between the SnO2 lattice and the OH on the surface.The limiting cd below which hydrogen was not observed was 3·052 × 10−4 A/cm2. After about 1 s, the polarization potential at this cd had a constant value dependent upon the logarithm of the electrolyte concentration and the nature of the electrolyte. This influence is interpreted as the adsorption of ions on the SnO2 lattice and the change of the concentration of the Sn—O—H, and, consequently, the change of the specific charge of the electrode surface.