Atomistic Explanation for Interlayer Charge Transfer in Metal-Semiconductor Nanocomposites: The Case of Silver and Anatase.

A concerted theoretical and experimental investigation of the silver/anatase hybrid nanocomposite, a very promising material for advanced sensing applications, is presented. We measure its exceptional electrochemical virtues in terms of current densities and reproducibility, providing their explanation at the atomic-scale level and demonstrating how and why silver acts as a positive electrode. Using periodic plane-wave DFT calculations, we estimate the overall amount of electron transfer toward the semiconductor side of the interface at equilibrium. Suitably designed (photo)electrochemical experiments strictly agree, both qualitatively and quantitatively, with the theoretical charge transfer estimates. The unique permanent charge separation occurring in the device is possible because of the favorable synergy of Ag and TiO2, which exploits in a favorable band alignment, while the electron-hole recombination rate and carrier mobility decrease when electrons cross the metal-semiconductor interface. Finally, the hybrid material is proven to be extremely robust against aging, showing complete regeneration, even after 1 year.