Capacitive properties of RuO2-coated titanium electrodes prepared by the alkoxide ink procedure

The capacitive properties of titanium electrodes with an active porous RuO2 coating were investigated in H2SO4 and NaCl solution by cyclic voltammetry and electrochemical impedance spectroscopy. Electrodes with two different masses of coating (thin and thick coating) were prepared from an ink suspension of the oxide synthesized by hydrolysis of ruthenium-ethoxide in ethanolic solution. The capacitive characteristics were found to be dependent on the coating mass and the electrolyte composition. It was shown that the impedance data of the prepared electrodes, registered at the open circuit potential, can be interpreted by a transmission line model of the equivalent electrical circuit. In this interpretation, the number of parallel branches containing resistor and capacitor in series is different for thin and thick coatings and in different electrolytes. More branches were required to describe the impedance behavior of the thick coating and to simulate the impedance data in NaCl solution. Simulation of the impedance data with the transmission line model of the equivalent circuit was also used to analyze the distribution of capacitance throughout the porous coating. The simulation indicated a more pronounced contribution of the capacitance of the outer coating layer to the total coating capacitance in the case of the proton-rich electrolyte. On the other hand, the presence of chloride ions in the electrolyte promoted a charging process at the inner coating surface, which is hardly accessible to the electrolyte.