The increasing concern in the detection of various forms of oxygen in gases mixtures calls for the development of highly sensitive sensor devices, operating on electrochemical principles. In this case for the understanding and determination of simplified models of sensor operation mechanisms the most informative method is electrochemical impedance spectroscopy (EIS). It became possible to represent the individual electrochemical processes, using simple circuit elements from the EIS data [1]. The present study focuses on understanding the role of the thickness of TiO2/ RuO2 electrode composition in the electrochemical behavior of electrode and identifying the sources of capacitance [2]. The goal is achieved by study of EIS spectra of TiO2/ RuO2 electrodes with different thickness of RuO2 coatings (δ=0,5 nm, 5 nm, 95 nm) in contact with air. The impedance spectra were taken in a two electrode cell with TiO2/ RuO2 electrodes using an Autolab-30 PGSTAT302N Metrohm Autolab equipped with FRA assembly unit within the range from 10–2 to 106 Hz. The distance of clips was kept constant (e.g., 20 mm) for all measurements. Procedure was controlled by Autolab 4.9 software with post processing in Zview 2.0. The electrochemical reactions were simulated by the method of equivalent circuits. The simulations of the EIS spectra influence of RuO2 coatings and its thickness on electrochemical properties of the electrodes. The pure TiO2 has another equivalent circuit than TiO2/RuO2 electrode composition. Such circuit is  typical for the systems with separate bulk layers present between the Ti/TiO2, and Double Electric layer on the TiO2 surface formed by adsorption of oxygen (the presence of oxygen creates an additional element with an inductance). The total capacitance in this case more than in 2 times greater than the capacitance of the TiO2/RuO2 electrode (1,2 and 0,5 respectively). The RuO2 coating eliminates the influence of the Ti/TiO2 bulk and the system works only in reaction with oxygen mode.