Electrochemical impedance spectroscopy, photoelectron spectroscopy, and Kelvin probe measurements on various TiO 2 single-crystal surfaces show that the position of the Fermi level and the conduction band minimum depend significantly on the sample environment (vacuum, air, water vapor, and aqueous or aprotic electrolyte solutions). In most cases, the conduction-band minimum increases in the series: anatase < rutile < brookite. The offset between anatase and rutile indicates a type II staggered alignment if the environment is vacuum, air, water vapor, or aprotic electrolyte solution, but a type IV aligned configuration is found in an aqueous electrolyte solution. The photoelectron spectra in water vapor reveal a strong upshift of the conduction band, which is nearly reversible in the early stages of water/titania interactions. Our results rationalize various earlier contradictions and highlight the need for proper analytical techniques and experimental conditions for investigation of the band energetics, which is relevant to practical applications of titania materials.

Titanium dioxide (anatase, rutile) and quasi-amorphous tin dioxide are prepared on F-doped SnO2 in the form of dense thin films, which can serve as electron-selective layers in perovskite solar cells and dye-sensitized solar cells (DSSCs). The present study brings new data about electronic and electrochemical properties of these films at the authentic conditions occurring in a dye-sensitized solar cell (DSSC). Hydrolysis of TiCl4 provides pure rutile TiO2 at low temperatures, but TiO2 (anatase) grows in these layers upon calcination. In acetonitrile medium, the flat band potential of TiO2 (rutile) is more negative than that of TiO2 (anatase). This is opposite ordering to that observed in aqueous media. The energy of conduction band minimum of TiO2 (anatase) equals −4.15 ± 0.07 eV at the conditions mimicking the DSSC’s environment. Electrochemical reductive doping of SnO2 provides a material with the most negative flat band potential and the largest overpotential for the reduction of I3 –, Co­(bpy)3 3+, and Cu­(tmby)2 2+. Voltammetric screening of all the electrode materials in six different electrolyte solutions, relevant to DSSC applications, gives salient information about the mediator type and effects of calcination and the addition of 4-tert-butylpyridine. These data provide novel inputs for optimization of DSSCs and for perovskite photovoltaics, too.

The effect of particle size and support on the catalytic performance of supported subnanometer copper clusters was investigated in the oxidative dehydrogenation of cyclohexene. From among the investigated seven size-selected subnanometer copper particles between a single atom and clusters containing 2 to 7 atoms, the highest activity was observed for the titania-supported copper tetramer with 100 % selectivity towards benzene production, and being about an order of magnitude more active than all the other investigated cluster sizes on the same support, but also the same tetramer on the other supports Al2O3, SiO2, and SnO2. In addition to the profound effect of clusters size on activity and with Cu4 outstanding from the studied series, Cu4 clusters supported on SiO2 provide an example of tuning selectivity through support effects when this particular catalyst produces also cyclohexadiene with about 30% selectivity. Titania-supported Cu5 and Cu7 clusters supported on TiO2 produce a high fraction of cyclohexadiene in contrary to their neighbors, while Cu4 and Cu6 produce solely benzene without any combustion, thus representing odd-even oscillation of selectivity with the number of atoms in the cluster.