Application of Supercritical CO2 Emulsified Electrolyte in Cathodic Deposition of Metal Oxides

Metal oxides, such as TiO₂ and ZnO, have been extensively investigated to foster their applications in various technologically important fields. There are many synthetic approaches proposed to fabricate metal oxide thin films. Among the different synthetic routes, electrochemical deposition affords an effective process for production of metal oxide thin films. Properties of the metal oxide films are highly dependent on desorption of gas generated on the surface of cathode, which can affect the pore structure of the porous metal oxide films deposited. Generation rate of hydroxyl ions on the surface of cathode and removal rate of the hydroxyl ions away from the surface of cathode can affect local pH on the surface cathode, which can affect grain size of the metal oxide formed.

Supercritical CO₂ (sc-CO₂) emulsified electrolyte (SCE) is known to be effective in affecting desorption rate of gas formed on the surface of cathode, and influence transfer efficiency of reactive species to the surface of cathode. Therefore, properties of the TiO₂ and ZnO thin films are expected to be influenced by the properties of the emulsion.  

In this work, a sc-CO₂-assisted galvanostatic cathodic deposition process is developed for preparation of TiO₂ and ZnO thin films with high structural uniformity. TiO₂ and ZnO are deposited cathodically on a conductive substrate in a two-compartment cell under a fixed current density, in which platinum foil is employed as the counter electrode. Influences of sc-CO₂ and reaction pressure on the crystal growth of TiO₂ and ZnO thin films were investigated. The present synthetic approach could be further extended to obtain other metal oxide thin films such as SnO₂, CuO, NiO and so on.