Electrochemistry of the Indium-Tin Oxide Electrode in 1 M NaOH Electrolyte

Electrochemical behavior of the bare indium-tin oxide (ITO) electrode in 1 M NaOH electrolyte has been studied in a wide range of current density and applied charge in view of its possible application as a counterelectrode in rare earth optical windows. Nature and kinetics of both cathodic and anodic processes developed on ITO depend on electrolyte composition as well as on transformations occurring with the electrode. Contribution of oxygen vacancies and ions is crucial for the electrochemical behavior of ITO. At the cathodic polarization, the electrode components are deeply reduced so that ITO is gradually and irreversibly converted to a metallic mirror with a noticeable decrease of oxygen content. At high anodic current density, the ITO electrode undergoes modifications and its conductivity decreases probably also due to the change of oxygen content in the oxides lattice. A phenomenological description of all the processes involved in ITO electrochemical performance and their reversibility is proposed and discussed. A stable operation of ITO in electrochemical devices can be achieved only in the case of usage of external RedOx dissolved in the electrolyte or deposited on the ITO electrode. Such active components could be selected from the different systems studied for flat panel displays.