The effect of the addition of colloidal iridium oxide into sol–gel obtained titanium and ruthenium oxide coatings on titanium on their electrochemical properties

Electrochemical properties of sol–gel processed Ti0.6Ir0.4O2 and Ti0.6Ru0.3Ir0.1O2 coatings on titanium substrate were investigated using cyclic voltammetry, polarization measurements and electrochemical impedance spectroscopy and compared to the properties of Ti0.6Ru0.4O2 coating. The role of iridium oxide in the improvement of the electrocatalytic, capacitive and stability properties of titanium anodes activated by a RuO2–TiO2 coating is discussed. The oxide sols were prepared by forced hydrolysis of the metal chlorides. The characterization by dynamic light scattering and X-ray diffraction showed that polydisperse oxide sols were obtained with the particles tending to form agglomerates. The presence of IrO2 causes a suppression of the X-ray diffraction peaks of TiO2 and RuO2 in the sol–gel prepared Ti0.6Ir0.4O2 and Ti0.6Ru0.3Ir0.1O2 coatings. The IrO2-containing coatings had an enhanced charge storage ability and activity for the oxygen evolution reaction (OER) in comparison to Ti0.6Ru0.4O2 coating. The voltammogram of the Ti0.6Ir0.4O2/Ti electrode showed well-resolved peaks related to Ir redox transitions, which are responsible for the enhanced charge storage ability of IrO2-containing coatings. Redox transitions of Ir were also registered in the high-frequency domain of the ac impedance spectra of the coatings as a semicircle with characteristics insensitive to the electrolyte composition and to the electrode potential prior to OER. However, the semicircle characteristics were different for the two IrO2-containing coatings, as well as at potentials outside the OER in comparison to those at which the OER occurs.