Hydrogenation process ofTiO2/BiVO4/PEDOT:PSS observed by XPS method

Titania nanotubes synthesis was based on a two-stage anodization process at water/ethylene glycol (5%/95%) electrolyte containing 0.27 M NH4F and 1 M H3PO4 described previously. Anodization process was performed in two-electrode cell compartment using platinum mesh as a cathode. The distance between electrodes was about 2 cm. The anodization voltage was kept at 40 V for 2 h. As prepared electrodes were immersed for 12 h in 0.5% wt aqueous solution of oxalic acid to remove inhomogeneous layer of nanotubular TiO2. Then, the anodization procedure was repeated at the same conditions. Such two-step procedure allows the uniform, nanotubular layer to be obtained. Finally, electrodes were annealed at a temperature of 450 °C for 2 h (heating rate: 2 °C min-1) in order to obtain crystalline phase of TiO2.
Annealed titania nanotubes and titania nanotubes covered by BiVO4 were subjected to cathodic polarization in 1 M H2SO4 electrolyte. The potential of working electrode during hydrogenation was equal to -1.5 V vs Ag/AgCl (0.1 M KCl) and process lasted for 60 s. The hydrogenation process significantly affects the TiO2 conductivity and specific capacitance. After hydrogenation process samples were named as Ti/TiO2:H/BiVO4:H. 
Result of hydrogenation process was observed by XPS method.