Although n-type titanium dioxide (TiO2) is a promising substrate for photogeneration of hydrogen from water, most attempts at doping this material so that it absorbs light in the visible region of the solar spectrum have met with limited success. We synthesized a chemically modified n-type TiO2 by controlled combustion of Ti metal in a natural gas flame. This material, in which carbon substitutes for some of the lattice oxygen atoms, absorbs light at wavelengths below 535 nanometers and has a lower band-gap energy than rutile (2.32 versus 3.00 electron volts). At an applied potential of 0.3 volt, chemically modified n-type TiO2 performs water splitting with a total conversion efficiency of 11% and a maximum photoconversion efficiency of 8.35% when illuminated at 40 milliwatts per square centimeter. The latter value compares favorably with a maximum photoconversion efficiency of 1% for n-type TiO2 biased at 0.6 volt.

0.15, is synthesized by controlled combustion of Ti metal in a natural gas flame. This material absorbs light at wavelengths below 535 nm and has a lower band gap energy than rutile. At an applied potential of 0.3 V it performs water splitting with a total conversion efficiency of 11% and a maximum photoconversion efficiency of 8.35% when illuminated at 40 mW/cm -2 . The latter value compares favorably with a maximum photoconversion efficiency of 1% for n-type TiO 2 biased at 0.6 V. -(KHAN*, S. U. M.; AL-SHAHRY, M.; INGLER JR.

Semiconducting nanocrystalline thin films of n-Fe2O3 were synthesized by a spray−pyrolytic method. These films were used for the photoelectrochemical splitting of water to hydrogen and oxygen gases. The rates of photoelectrochemical splitting of water at these thin-film electrodes were found to depend on the spray time, substrate temperature, solvent composition in the spray solution, and the concentration of the spray solution. The maximum photocurrent density of 3.7 mA cm-2 at 0.7 V/saturated calomel electrode (SCE) was obtained at the n-Fe2O3 film synthesized using the optimum condition of substrate temperature of 350 °C, the spray time of 60 s, and the spray solution of 0.11 M FeCl3 in 100% ethanol. The band gap energy of this film was found 2.05 eV. The flatband potential of −0.74 V/SCE and the apparent donor density of 2.2 × 1020 cm-3 were found from the Mott−Schottky plots at the AC frequency of 1000 Hz. The n-Fe2O3 films synthesized using the optimum conditions gave rise to a total conversion efficiency of 4.92% and a practical photoconversion efficiency of 1.84% at an applied potential of 0.2 V/SCE at pH 14.

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