Energetics of Semiconductor ElectroddSolution Interfaces: EQCM Evidence for Charge-Compensating Cation Adsorption and Intercalation during Accumulation Layer Formation in the Titanium DioxiddAcetonitrile System

Combined reflectance, electrochemical quartz crystal microbalance, and conventional voltammetric measurements on high-area titanium dioxide electrodes in dry, electrolyte-containing solutions of acetonitrile show that electron accumulation layer formation is coupled directly to intercalation (e.g., Li+ or Na+) or to reversible adsorption (tetrabutylammonium ion) of charge compensating cations. Difficulty in achieving intercalation with these ions appears to account for the extreme negative shift of the flatband potential in acetonitrile, in comparison to aqueous solutions. More generally, the charge compensation based adsorptiordintercalation phenomenon appears to play a key role in defining the conduction band edge energetics of titanium dioxide (and presumably other metal oxides) in solution environments.