Efficient Photoelectrochemical Splitting of Water to H2 and O2 at Nanocrystalline Carbon Modified (CM)-n-TiO2 Thin Films
The carbon modified n-type titanium oxide (CM-n-TiO2) thin films were synthesized by flame oxidation of Ti metal sheets both flat and grooved and also by using combination of spray pyrolysis and flame oxidation of flat surface. Also undoped reference n-TiO2samples were also synthesized in an electric oven for comparison. Photoresponse of CM-n-TiO2 and n-TiO2 were evaluated by measuring the rates of water splitting to hydrogen and oxygen, in terms of observed photocurrent densities. Under the white light illumination of intensity of 100 mW cm-2 from the xenon lamp the photocurrent densities were found to be 1.60, 9.17, 11.44 and 14.68 mA cm-2 for optimized oven made n-TiO2 (sample1), flame made on flat surface (sample 2), on grooved surface (sample 3) and spray pyrolysis-flame made CM-n-TiO2 (sample 4) thin films at 0.477 V, 0.240 V, 0.242 V and 0.215 V biases respectively. The corresponding maximum photoconversion efficiencies for these thin films were found to be 1.2 %, 9.08 %, 11.31 % and 14.04 % for samples 1-4 respectively. Under monochromatic light illumination from the xenon lamp the maximum photoconversion efficiencies for samples 1-4 were found to be 0.94 %, 8.86 %, 11.16 % and 13.79 % respectively. However, under actual natural global AM 1.5 sunlight illumination of 1 sun, the maximum photoconversion efficiencies reduced to 0.67 %, 5.63 %, 7.62 % and 12.26 % for samples 1, 2, 4 and 3 respectively. These values compared well with those found under monochromatic light illumination from the xenon lamp. The increasing efficiencies were found consistent with lowering of band gaps from 2.9 eV for sample 1 to 2.65 eV and generation of mid-gap band at 1.6 eV for both samples 2 and 3 and 1.4 eV above the valence band for sample 4. Carbon contents were found to be 0.0, 17.60, 19.38 and 23.23 atom % for samples 1, 2, 3 and 4 respectively.
Maria K. Nowotny and Janusz Nowotny
Y. A. Shaban and S. U.M. Khan, "Efficient Photoelectrochemical Splitting of Water to H2 and O2 at Nanocrystalline Carbon Modified (CM)-n-TiO2 Thin Films", Solid State Phenomena, Vol. 162, pp. 179-201, 2010