Sensitization of TiO₂ Nanotube Arrays by Mixed Oxovanadium(IV) Complex for Enhanced Photoelectrochemical Cells Performance

An oxovanadium(IV) complex of ([Tp*VOL]) was employed to extend the system’s absorption window into the visible range and improve the photoactivity and performance of the titania nanotubular array-based photoanodes for application in photoelectrochemical cells. The Tp* ligand is donated to hydrotris(3,5-dimethyl pyrazolyl)borate, and the L ligand is donated to N, N-dialkyl-N^´-benzoylthiourea. The complex was synthesized from the reaction of vanadyl sulfate (VOSO₄), potassium tris(1 H-pyrazol-yl)borate and N, N-dialkyl-N^´-benzoylthiourea in methanol. Titania nanotube (TiNT) was fabricated by anodizing titanium foil in an organic media containing fluorine ion (98 vol% ethylene glycol and 0.3 wt% ammonium fluoride) at 20 V_DC at room temperature for 45, 120, 180, and 360 min. To produce anatase TiO₂, the anodized samples were calcined in a tube furnace for three hours at 500 °C with airflow. Dye-sensitized TiNT arrays were obtained by immersing TiNT in 10^− 4 mM [Tp*VOL] overnight at room temperature in the dark, rinsing with deionized water and drying under N₂. The lengths of the highly ordered tubes under optimized conditions were 1.4, 3.6, 3.9 and 5.6 μm. Dye-sensitized and nonsensitized TiNT photoanodes (standard) were used as working electrodes in photoelectrochemical cells utilizing 0.5 M Na₂SO₄ electrolyte. The photoelectrochemical responses of the dye-sensitized and standard photoanodes were examined based on their photocurrent density. The photocurrent density of dye-sensitized TiNT photoanodes was 4 times greater than the standard density. The photoelectrochemical response increased with increasing nanotube length, namely, from 0.24 to 3 mA/cm² at 1.0 V vs. SCE for lengths of 1.4 to 5.6 μm. This result suggested that the [Tp*VOL]-sensitized TiNTs can be applied as potential photoanode materials for photoelectrochemical cells.