SPECTROSCOPIC DETERMINATION OF FLAT-BAND POTENTIALS FOR POLYCRYSTALLINE TIO2 ELECTRODES IN MIXED-SOLVENT SYSTEMS

We report studies directed toward a quantitative understanding of the relationship between the flatband potential (V-fb) of a metal oxide se miconductor electrode (titanium dioxide) and the composition of a cont iguous electrolyte solution (water, methanol, ethanol, and acetonitril e each containing 0.2 mol dm(-3) tetrabutylammonium perchlorate). A re lationship between V-fb and the proton-generating ability of the elect rolyte solvent, as measured by the autoprotolysis constant of the pure solvent, is demonstrated. Additional studies have examined the depend ence of V-fb on the composition of a binary electrolyte solvent mixtur e (acetonitrile/ethylene carbonate and acetonitrile/water). We conclud e that the composition of the acetonitrile/ethylene carbonate mixture at the semiconductor-electrolyte solution interface (SLI) is similar t o that of the bulk solution. However, for an acetonitrile/water mixtur e there is preferential adsorption of water at the SLI. Finally, for a protic electrolyte solutions, the dependence of V-fb on the electrolyt ic solute was studied. Cations such as Li+ and Na+ are potential deter mining.