Vacuum Electrochemistry Approach to Investigate Electrical Double‐Layer Capacitances of Ionic Liquid for Epitaxial Thin‐Film Electrodes of TiO2 and SrO on Niobium‐Doped (001)SrTiO3

Abstract

AbstractNiobium‐doped (001)SrTiO3 (Nb:STO) single crystal, and epitaxial anatase (001)TiO2 and (001)SrO films, which were subsequently deposited on the Nb:STO by pulsed laser deposition, were electrochemically investigated with ionic liquid (IL) in a vacuum. After being prepared by cleaning and/or depositing the films, the electrode surfaces were characterized by observing the reflection of high‐energy electron diffraction, prior to the electrochemical measurements. Electrochemical impedance spectroscopy as well as cyclic voltammetry were then performed, and the electrical double‐layer (EDL) capacitance at their interfaces with the IL were successfully evaluated. The EDL capacitance of IL was several μF cm−2 for Nb:STO and gradually increased to over 10 μF cm−2 with an increase of the thickness of the deposited TiO2 films. In contrast, as SrO was being deposited, the EDL capacitance gradually decreased, approaching a constant value of about 1.4 μF cm−2, which was significantly smaller than those values achieved for TiO2 films and single‐crystal Nb:STO. For different oxide/IL interfaces, a possible correlation between their measured EDL capacitance and the ionicity of the oxides is discussed.