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It was found for the first time that controlling the charge density in oxide semiconductors with an acceptor was effective for improving the activity to photolysis of H 2 O. Although the photodecomposition activity of NiO supported on nondoped KTaO 3 was negligibly small, doping small amount of acceptors such as tri-or tetravalent cations to KTaO 3 increased the formation rate of H 2 and O 2 . In particular, it was found that NiO supported on KTaO 3 doped with 8 mol % Zr 4+ exhibits higher activity to the photocatalytic decomposition of H 2 O than that of a well-known photocatalyst of Pt/TiO 2 .

LaGaO,-based perovskite oxides doped with Sr and Mg exhibit high ionic conductivity over a wide range of oxygen partial pressure. In this study, the stability of LaGaO,-based oxide was investigated. The LaGaO,-based oxide was found to be very stable in reducing, oxidizing, and CO2 atmospheres. Solid oxide fuel cells (SOFCs) using LaGaO,-based perovskite-type oxide as the electrolyte were studied for use in intermediate-temperature SOFCs. The power-generation characteristics of cells were strongly affected by the electrodes. Both Ni and LnCoO, (Ln:rare earth) were suitable for use as anode and cathode, respectively. Rare-earth cations in the Ln site of the Co-based perovskite cathode also had a significant effect on the power-generation characteristics. In particular a high power density could be attained in the temperature range 973-1273 K by using a doped SmCoO, for the cathode. Among the examined alkaline earth cations, Srdoped SmCoO, exhibits the smallest cathodic overpotential resulting in the highest power density. The electrical conductivity of SmCoO3 increased with increasing Sr doped into the Sm site and attained a maximum at Sm0 ,Sr,,CoO3. The cathodic overpotential and internal resistance of the cell exhibited almost the opposite dependence on the amount of doped Sr. Consequently, the power density of the cell was a maximum when Sm0 ,Sr,,CoO, was used as the cathode. For this cell, the maximum power density was as high as 0.58 W/cm2 at 1073 K, even though a 0.5 mm thick electrolyte was used. This study revealed that a LaGaO,-based oxide for electrolyte and a SmCoO,-based oxide for the cathode are promising components for SOFCs operating at intermediate temperature.

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Preparation of CuO thin films by decomposition of self-assembled multibilayer films as a molecular template was investigated. Furthermore, the CO 2 sensing property of the resultant CuO thin films on a porous BaTiO 3 was investigated as a capacitive type sensor. Self-assembled bilayer films of a few 1000 layers thickness can be readily obtained by casting an aqueous suspension composed of dimethyldihexadecylammoniun bromide (DC1-16), Cu(CH 3 CO 2 ) 2 , hexadecylethylenediamine and poly(vinyl alcohol). Divalent copper ions (Cu2+) which are associated with two hexadecylethylenediamine molecules were arranged in the hydrophobic layer of the multibilayer film. Rapid heating to the combustion temperature of DC1-16 was desirable for removing organic molecules in the multibilayer template. Thin films of CuO can be obtained by calcination at temperatures higher than 573 K. The resultant CuO thin films were porous and consisted of fine particles. The capacitance of CuO thin films prepared from self-assembled multibilayer films as a molecular template on the BaTiO 3 porous substrate exhibited a high sensitivity to CO 2 , which is twice that of a conventional mixed oxide capacitor of CuO-BaTiO 3. The capacitance of CuO thin films on BaTiO 3 increases with increasing CO 2 concentration in the range from 100 ppm to 50% at 873 K. Consequently, it is concluded that CuO thin films on BaTiO 3 were appropriate capacitive type CO 2 sensors.improve the sensitivity and the response characteristics of