Photo-electrochemical hydrogen generation using band-gap modified nanotubular titanium oxide in solar light

Anodization of Ti in acidified fluoride solution results in an ordered nanotubular titanium oxide surface. In this study, vertically oriented arrays of TiO2 nanotubes were prepared by incorporating nitrate and phosphate species during the anodization process. These nanotubes were annealed at 650 °C in a carbonaceous atmosphere using a chemical vapor deposition (CVD) furnace for a brief period. The carbon-modified nanotubular TiO2 produced a photo-current density of more than 2.75 mA cm−2 at 0.2 VAg/AgCl under solar light illumination. This photo-current density corresponds to a hydrogen evolution rate of about 11 l h−1 using a photo-anode of 1 m2 area. The enhanced hydrogen evolution behavior of carbon-modified nanotubular TiO2 is highly reproducible and sustainable for long duration. Annealed (at 350 °C in nitrogen atmosphere) TiO2 nanotubes showed improved photo-activity as compared to the as-anodized or thermally oxidized TiO2 photo-anodes.