Visible light active hydrogen modified (HM)-n-TiO 2 thin films for photoelectrochemical splitting of water

Abstract

Visible light active hydrogen modified n-type titanium oxide (HM-n-TiO 2) thin films were synthesized by thermal oxidation of Ti metal sheet (Alfa Co. 0.25 mm thick) in an electric oven followed by incorporation of hydrogen electrochemically under cathodic polarization at −1.6 V vs Pt. The photoresponse of the HM-n-TiO 2 was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen in terms of photocurrent density, J p. The optimized electric oven-made n-TiO 2 and HM-n-TiO 2 photoelectrodes showed photocurrent densities of 0.2 mA cm −2 and 1.60 mA cm −2, respectively, at a measured potential of −0.4 V vs Pt at illumination intensity of 100 mW cm −2 from a 150 W xenon lamp. This indicated an eightfold increase in photocurrent density for HM-n-TiO 2 compared to oven-made n-TiO 2 at the same measured electrode potential. The band-gap energy of HM-n-TiO 2 was found to be 2.7 eV compared to 2.82 eV for electric oven-made n-TiO 2 and a mid-gap band at 1.67 eV above the valence band was also observed. The HM-n-TiO 2 thin film photoelectrodes were characterized using photocurrent density under monochromatic light illumination and UV–Vis spectral measurements.