Adsorption Behavior of the 1,3-Dimethylimidazolium Thiocyanate and Tetracyanoborate Ionic Liquids at Anatase (101) Surface

Abstract

The adsorption behavior of the ionic liquids 1,3-dimethylimidazolium thiocyanate and 1,3-dimethylimidazolium tetracyanoborate on the anatase (101) surface is studied through theoretical methods. This includes a comparison of the PBE and PBE0 functionals as well as the D3 and D3M+ dispersion correction schemes for the calculation of energetic and structural properties. The PBE functional was found to underestimate interaction energies, and the D3 dispersion correction was observed to overbind. While the surface titanium atoms predominantly form contact with anion’s nitrogen atoms, the oxygen atoms of anatase interact in hydrogen-bond-like structures with the acidic hydrogen atoms of the imidazolium cation in addition to ubiquitous electrostatic and dispersive interactions. Ionic liquid ion pairs remain stable after adsorption and closely match the geometry of the isolated ions. A band shift of the density of states of TiO2, possibly resulting in higher values of the open-circuit voltage in complete solar cells, is attributed to the adsorption, which might be interesting for application of these ionic liquids in real dye-sensitized solar cell devices.