Effects of Pressure in Cathodic Deposition of TiO2 and SnO2 with Supercritical CO2 Emulsified Electrolyte

•Report the effect of pressure in deposition of metal oxides in aqueous solution.•Crystalline TiO2 and SnO2 were obtained directly by cathodic deposition.•Crystallinity of the TiO2 and SnO2 was improved with an increase in the pressure.•Morphology of the TiO2 films was affected by the high pressure.

This study reports the effect of the high pressure on properties, especially the crystallinity, of the TiO2 and SnO2 films cathodically deposited in supercritical CO2 emulsified electrolyte. The as-deposited metal oxides are usually amorphous when cathodic deposition is applied. An additional heat treatment process is needed to have crystalline metal oxides. In this study, the TiO2 and SnO2 thin films cathodically deposited at elevated pressure showed an improvement in the crystallinity with an increase in the pressure using X-ray diffraction analysis. The high-resolution transmission electron microscopy and selected-area electron diffraction confirmed that the TiO2 deposited at 35 MPa had the anatase crystal structure. An enhancement in the charge carrier dynamics at the TiO2 electrode/electrolyte interface with an increase in the pressure was observed from the electrochemical impedance spectroscopy, which is a result of the improved crystallinity. The effect of the pressure on the crystallinity of the SnO2 was more obvious than that on the TiO2. Grain size of the SnO2 films estimated by the Scherrer equation was increased from 3.5 to 14.8 nm when the pressure was increased from 5 to 25 MPa.

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