Key Engineering Materials Vol. 485

Abstract: Single phase specimen of K_0.12TiO₂ with hollandite-type structure was successfully synthesized by the solid-state reaction under Ar/H₂ atomosphere. K⁺ ions were partially extracted from the parent K_0.12TiO₂ specimen by the HCl treatment. The K⁺-extracted K_0.08TiO₂ specimen worked as a rechargeable electrode material. An initial capacity of 92 mAh/g (cut-off voltage: 1.0 V) could be achieved, which approximately correspond to the composition Li_0.28TiO₂. A reversible capacity after 50 cycles was about 50 mAh/g.

Abstract: SnO₂ nanoparticles were successfully synthesized by the microwave heating. The crystallite size of the SnO₂ nanoparticles was estimated to be about 3 nm from the Scherre’s equation. The initial lithium insertion capacity of the SnO₂ nanoparticles was 2110 mAh/g which is larger than that of the micro-sized commercial SnO₂ product. The rechargeable capacity at 10 cycles was 1060 mAh/g, and the capacity retention over the tenth cycles was about 50 %.

Abstract: Highly oriented and polycrystalline Gd₂O₃ doped CeO₂ thin films were prepared on α-Al₂O₃(0001) substrates by chemical vapor deposition, using Ce(C₅H₄C₂H₅)₃ and Gd(C₅H₄C₂H₅)₃ as precursors. The compositions of the films were controlled by optimizing the vaporization pressure of Gd precursor under the constant vaporization condition of Ce precursor. In-plane electrical conductivities of the films at various temperatures and oxygen partial pressures were evaluated by electrochemical impedance spectroscopy measurements. The activation energy of the film was determined as 0.94 eV, which is comparable with that of pulsed laser deposited films.

Abstract: Spherical samarium doped ceria (Ce_0.8Sm_0.2O_1.9, SDC) powders having high specific surface area (SSA) were successfully synthesized by carbon-assisted spray pyrolysis (CASP). Saccharides, such as monosaccharides and disaccharides, or organic acids were used as carbon sources. The physical and chemical properties of these powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Thermo gravimetry-Differential Thermal Analysis (TG-DTA), and BET. Decarbonized powders obtained by this method exhibit spherical morphologies and nano- and submicron-sizes. The SSA of SDC obtained from CASP was more than seven times higher than that obtained from conventional spray pyrolysis (CSP). The SSA of the decarbonized SDC powders obtained by calcination at 900 °C was estimated to be approximately 70 m²/g by using the BET method. The relative density of SDC obtained from CASP was higher than that obtained from CSP. The relative density of the SDC pellet was highest (96 %) when it was sintered at 1400 °C.

Abstract: To determine the effect of the annealing atmosphere on oxygen diffusion through Ba_0.95La_0.05FeO_3-d pellets, ¹⁸O₂ tracer diffusion and high-resolution secondary ion mapping were performed. When annealing in air, the ¹⁸O concentration around the surface up to a depth of 40 µm was almost constant. On the other hand, when annealing in vacuum, the ¹⁸O concentration obviously decreased. High-resolution secondary ion mapping indicated that the ¹⁸O concentration around the grain boundary was reduced. These results suggested that the grain boundary of BLF annealed in vacuum prevents oxygen diffusion.

Abstract: The (ZrO₂-1.6P₂O₅)-PTFE composite electrolytes have been prepared by mixing PTFE powders with different particle sizes and the shell-core-type ZrO₂-1.6P₂O₅ electrolyte, synthesized by solid state reaction with diammonium hydrogen phosphate, to improve the mechanical strength of the electrolyte. The H₂ gas permeability decreased and the cell performances improved with decreasing PTFE-particle size. The aging at 0.4 V above 443 K enhanced the ITFC performance owing to the penetration of the electrolyte to the carbon paper. The maximum output power enhanced by 63% after 15 h of aging at 573 K.

Abstract: TiO₂ nanopowders were synthesized hydrothermally from TiCl₄ aqueous solution. Particle diameters could be varied in the range 5–65 nm by controlling the synthesis time and temperature. Dye-sensitized solar cells were fabricated using the powders and their power generation efficiencies were evaluated.

Abstract: TiO2 nanotube array films were synthesized by the anodic oxidation of a Ti plate in an NH4F electrolyte. The thickness of the films was dependent upon the oxidation time. Nanotube clusters were produced when the films were subjected to sonication. Pastes were subsequently prepared by mixing the nanotube clusters with TiO2 nanoparticles. The pastes were used to fabricate photoelectrodes of dye-sensitized solar cells. The generation efficiencies of cells with TiO₂ nanotube clusters were lower than those of cells without these clusters. TiO₂ nanotube clusters were very large, and therefore, they might have intercepted the ionic transport.

Abstract: In this study, we attempted to develop a low-cost dye-sensitized solar cell (DSC) by substituting a screen-printed carbon electrode for the conventional platinum counter electrode. Carbon electrodes were formed from mixtures of activated carbon, carbon nanofiber, carbon black, and a resin. The best carbon electrode conversion efficiency obtained was approximately 90% that of a platinum-based electrode.

Abstract: Nanostructured ZnO films for use in dye-sensitized solar cells were fabricated by utilizing a chemical bath deposition process and a newly developed liquid–liquid process. Layered zinc hydroxides were first deposited on fluorine-doped tin oxide (FTO)-coated substrates and then heated at 450 °C in air to obtain ZnO. Cells were constructed by employing a quasi-solid-state polymer gel electrolyte. The performance of the cells with the ZnO films from the different deposition processes was compared and discussed in terms of the microstructure. Light-to-electricity conversion efficiency reached 2% in all the cells under full sunlight. The cells were kept for 500 h at room temperature, revealing that they maintained 90% of their initial performance.