Intrinsic Potential-Dependent Performances of a Sol-Gel-Prepared Electrocatalytic IrO2-TiO2 Coating of Dimensionally Stable Anodes

The electrochemical properties of a sol-gel-prepared IrO2-TiO2 coating on Ti were investigated from the standpoint of the charging/discharging behavior in 1.0A degrees mol dm(-3) H2SO4 and in 0.50A degrees mol dm(-3) NaCl, pH 2. The potential-dependent changes from low oxidation states of Ir, with low activity, to those of higher activity (enhanced pseudocapacitive performances) were analyzed at different charging/discharging rates by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed the distribution of Ir oxidation states through the coating, with lower ones being placed largely in the internal, hardly accessible, parts of the coating. The transition to higher oxidation states appears as crucial for the full development of pseudocapacitive performances. This transition occurs much easier in the NaCl than in the H2SO4 solution, since the potentials of redox transitions of Ir are much closer due to lower hydrogen ion concentration in NaCl solution. As a consequence, a unique overall coating capacitance was registered in both solutions