Characterization of IrO₂-SnO₂ Films Prepared by Physical Vapor Deposition at Ambient Temperature

Abstract

The synthesis of thin-film electrodes of IrO₂-SnO₂ was carried out at room temperature by rf-magnetron sputtering, and their characterization was attained through electrochemical (cyclic voltammogram, electrochemical impedance spectrometry, polarization curves) as well as structural tests (Rutherford backscattering spectroscopy, X-ray diffraction, SEM). Further information was obtained studying the catalytic properties of films towards the chlorine evolution reaction, which has been taken into account as a model reaction. Films appear amorphous, and the fact that their density is in good agreement with the weighted average of component oxide densities may indicate that no solid solution has formed. As a result of their compact structure, coatings richer in iridium oxide do not show a high availability in electrocatalytic sites; tin oxide addition appears fundamental in terms of catalytic activity and cost of materials. The “valve metal” oxide acts as a dispersing phase for the “noble metal” oxide: the number of electroactive sites increases significantly when moving from IrO₂ 100 % to IrO₂-SnO₂ 50:50 % mol, and the active material thickness increases too, reaching more than 100 active monolayers. However, a high (re)activity generally involves a high tendency to dissolution: iridium and tin sites dissolve with the same ease and, in fact, the IrO₂-SnO₂ 50:50 % mol is both the most active and the less stable among the studied coatings.