Kazuhiro Yamamoto

To avoid the proneness to degradation due to coking in the operation of solid oxide fuel cells (SOFCs) directly running on methane (CH4) fuels, a modified porous anode of the Ni1−XCoX/YSZ (yttria-stabilized zirconia) cermet prepared by an impregnation method is presented. The influence of the Co alloying content on the cermet microstructure, SOFC characteristics, and prolonged cell performance stability has been studied. Co was incorporated into Ni and formed a solid solution of Ni1−XCoX alloy connected with the YSZ as the cermet anode. The porous microstructure of the Ni1−XCoX/YSZ cermet anode formed by sintering exhibited a grain growth with an increase in the Co alloying content. The electrochemical performance of the cells consisting of the Ni1−XCoX/YSZ cermet anode, the YSZ electrolyte, and the LSM (La0.8Sr0.2MnO3) cathode showed an enhancement by the Ni1−XCoX impregnation treatment for the respective supply of H2 and CH4 to the anode. The cell using the Ni0.75Co0.25/YSZ cermet anode (the Ni0.75Co0.25 cell) showed the highest cell performance among the cells tested. In particular, the performance enhancement of this cell was found to be more significant for CH4 than that for H2; a 45% increase in the maximum power density for CH4 and a 17% increase for H2 at 750 °C compared with the performance of the cell using the Ni/YSZ cermet anode. Furthermore, the prolonged cell performance stability with a continuous CH4 supply was found for the Ni0.85Co0.15 and Ni0.75Co0.25 cells at least for 60 h at 750 °C. These enhancement effects were caused by the optimum porous microstructure of the cermet anode with the low anodic polarization resistance.

n-type GaN photoanodes used for water splitting have stability problems. One means of resolving this is loading NiO catalyst on the n-type GaN surface. Aqueous electrolytes H2SO4, HCl, KOH, and NaOH are usually used for photoelectrochemical water splitting. However, suitable electrolytes for the NiO-loading on n-type GaN photoelectrode have not yet been evaluated. Therefore, we investigated the effects of changing electrolytes used for NiO-loading in this study. The photocurrent of NiO-loading on n-type GaN increased when KOH and NaOH electrolytes were used. In addition, the surfaces showed no corrosion after reaction when these electrolytes were used. However, the photocurrent was not stable using KOH electrolyte. Interestingly, stable photocurrent was observed with when the NaOH electrolyte was used. In the case of H2SO4, the photocurrent of GaN did not change with and without NiO. The surface morphologies became rough because of GaN corrosion, and NiO dissolved in the H2SO4 electrolyte. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In this feature article, we highlight our works on compositional and structural dependence of up converting rare earth (RE) fluorides obtained through ethylenediamine tetraacetic acid (EDTA) assisted hydrothermal synthesis. Various nanostructures were obtained by tuning of experimental conditions, such as precursor's concentration, degree of doping, reaction time and solvent used during synthesis. We correlated in detail the structural, morphological and optical properties of YF3 and NaYF4 compounds co-doped with Yb3+ and Er3+ (introduced in total mol% of 8 and 20). For this purpose, X-ray powder diffraction, scanning and transmission electron microscopy, energy dispersive X-ray and Furrier transform infrared spectroscopy, as well as, the photoluminescence spectra and decay times were recorded and analyzed. The particle size and phase content were found to be dependent on the nucleation rate, which, in turn, was governed by the precursor concentration, degree of doping and solvent type. The transformation from cubic to hexagonal NaYF4:Yb3+/Er3+ phase was found to be sensitive to the reaction time and precursors concentration, while the crystallization of orthorhombic YF3:Yb3+/Er3+ phase is achieved through lowering of dopants concentration or by changing of solvent during hydrothermal treatment. The up-conversion photoluminescence demonstrated morphology and crystal phase dependence and is found to be superior in microcrystalline samples, independent on their phase composition. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology japan. All rights reserved.

Owing to their unique optical properties, up-converting rare earth fluorides have attracted extensive attention in recent years. Varieties of synthesis procedures which generate nano-and micro-crystals with controllable compositions have been reported. In the vast majority, surfactants, complexing agents and solvents play essential role in controlling particles morphology and surface characteristics. Here we report on a rapid solvothermal synthesis (200 degrees C, 2 h) of either PEG or PVP capped NaYF4:Yb3+/Er3+ particles. Their structural, morphological and luminescence characteristics have been studied based on X-ray powder diffractometry (XRPD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM) and photoluminescence measurements. Both polymers proved to be a good structure directing agents enabling generation of the well crystalline polymer coated up-converting particles with efficient emissions in visible spectrum. It was shown that generation of the hexagonal P63/m beta-NaYF4:Yb3+/Er3+ phase with the most efficient green emission (CIE 0.31, 0.66) is enhanced when PVP is used during synthesis, while promotion of the cubic Fm-3m alpha-NaYF4:Yb3+/Er3+ phase that has a yellowish spectral output (CIE 0.41, 0.56) was observed in the particles produced in the presence of PEG. Beneficial effect on the luminescence intensity was observed with additional particles annealing in argon atmosphere. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

The n-type GaN photoelectrode is suitable for hydrogen generation from water because it can split water without bias. However, the n-type GaN photoelectrode has the anodic corrosion problem caused by the etching of the GaN. This problem can be resolved by NiO loading on GaN. The reported method of NiO loading on GaN surface was carried out by coating the surface by diluted metal organic decomposition (MOD) and high-temperature annealing. Since no NiO loading methods using Ni(OH)(2) dispersed solution and low-temperature annealing have been reported, in this study, we attempted NiO loading Ni(OH)(2) dispersed solution. Experimental results confirmed that the method can be easily performed and effective. In addition, we also compared the photoelectrochemical properties of the n-type GaN samples obtain by Ni(OH)(2) loaded using four different Ni(OH)(2) synthetic methods, loading by NiO-MOD, and no-NiO loading. The photocurrent densities of all samples loaded using Ni(OH)(2) dispersed solution increased compared to samples without NiO and with NiO-MOD. The photocurrent densities and stabilities were affected by the NiO shape and density which were found to be related with the method of synthesizing the Ni(OH)(2) dispersed solutions. The effects of NiO shape and density on the photocurrent density and stability are also discussed. (C) 2016 The Electrochemical Society. All rights reserved.

A core-shell anode consisting of nickel-gadolinium-doped-ceria (Ni-GDC) nanocubes was directly fabricated by a chemical process in a solution containing a nickel source and GDC nanocubes covered with highly reactive {001} facets. The cermet anode effectively generated a Ni metal framework even at 500 degrees C with the growth of the Ni spheres. Anode fabrication at such a low temperature without any sintering could insert a finely nanostructured layer close to the interface between the electrolyte and the anode. The maximum power density of the attractive anode was 97 mW cm(-2), which is higher than that of a conventional NiO-GDC anode prepared by an aerosol process at 55 mW cm(-2) and 600 degrees C, followed by sintering at 1300 degrees C. Furthermore, the macro-and microstructure of the Ni-GDC-nanocube anode were preserved before and after the power-generation test at 700 degrees C. Especially, the reactive {001} facets were stabled even after generation test, which served to reduce the activation energy for fuel oxidation successfully.

Using single-walled carbon nanotubes (SWCNTs) for energy harvesting and storage have attracted much attention recently because SWCNTs have supercapacity performance. In this paper, we report a simple electromechanical approach for the generation of induced electrical potential by the compression of a SWCNT-triggered sodium deoxycholate hydrogel. This hydrogel enhances the electrical potential generated under compression, and this is mainly because of the generation of hydroelectric power by the flow of water over the SWCNTs. The induced voltage was 63.1 mV upon the compression of a 4% SWCNT hydrogel to a compression ratio of 50%, which is superior to values reported previously. The enhancement in hydroelectric potential increased with SWCNT loading in the hydrogel and with the compression ratio because of an enhancement of the impact frequency between water molecules and the SWCNTs. (C) 2014 AIP Publishing LLC.

Gadolinium-doped ceria (GDC) nanocubes with highly reactive {001) facets were synthesized as an anode material for solid-oxide fuel cells by organic-ligand-assisted hydrothermal treatment with a water-soluble amino acid, 6-amino hexanoic acid (AHA). An aerosol technique was applied to fabricate a NiO-GDC nanocube composite with water as a green solvent. The NiO-GDC nanocube composite was easily sintered even at a temperature of 1100 degrees C, while the conventional NiO-GDC composite covered with the most stable {1 1 1) facets was sintered at 1300 degrees C. Sintering at such a low temperature inhibited undesirable coarsening of NiO and GDC particles, resulting in an enlarged, triple-phase boundary (TPB). The NiO-GDC nanocube composite anode with the enlarged TPB exhibited a rather low area specific resistance of 0.14 Omega cm(2) compared with the conventional NiO-GDC composite anode's resistance of 0.58 Omega cm(2) when operated at 600 degrees C. (C) 2014 Elsevier Ltd. All rights reserved.

The mass production of highly dense oxides with high-temperature and high-pressure phases allows us to discover functional properties that have never been developed. To date, the quenching of highly dense materials at the gramme-level at ambient atmosphere has never been achieved. Here, we provide evidence of the formation of orthorhombic Fe2TiO4 from trigonal FeTiO3 as a result of the high-temperature (> 1250 K) and high-pressure (> 23 GPa) condition induced by the high collision energy of 150 gravity generated between steel balls. Ilmenite was steeply quenched by the surrounding atmosphere, when iron-rich ilmenite (Fe2TiO4) with a high-temperature and high-pressure phase was formed by planetary collisions and was released from the collision points between the balls. Our finding allows us to infer that such intense planetary collisions induced by high-energy ball milling contribute to the mass production of a high-temperature and high-pressure phase.

Our findings reveal an ordered-disordered phase transformation in LiNi0.5Mn1.5O4 triggered by sucrose. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local structure in sucrose-treated LiNi0.5Mn1.5O4. It was found that larger lattice strain in sucrose-induced disordered LiNi0.5Mn1.5O4 is attributed to Ni-site distortion.

The present study reports the design of a novel bioanode to deeply oxidize glucose in an enzymatic biofuel cell (EFC). This enzymatic glucose cell utilizes three co-immobilized enzymes: NAD-dependent glucose dehydrogenase (GDH), NAD(P)(+)-dependent gluconate-5-dehydrogenase (Ga5DH), and diaphorase (DI). Glucose is oxidized to gluconate by NAD-dependent GDH, gaining two electrons per glucose; the gluconate obtained as a by-product is oxidized at the C5 carbon to 5-keto-gluconate by Ga5DH. Operation of our bioanode enabled the oxidation of glucose in two stages, resulting in the gain of four electrons. The three-enzyme EFC provides a maximum power density of 10.51 +/- 1.72Wcm(-2), which is about 1.6 times higher than the maximum power density of an EFC using a bioanode based on the co-immobilization of two enzymes (GDH and DI). Our results hold promise for increasing the current density of EFCs, and for application in glucose biosensor.

Size-controllable TiO2 nanosheets with highly exposed {001} facets were synthesized by a hydrothermal method. The particle sizes ranged from 25 nm to submicrometres by carefully adjusting the F/Ti molar ratio. TiO2 nanosheets smaller than 100 nm have higher photocatalytic activity and are highly stable in degradation of organic dyes.

Abstract (italic typeface) Multi-walled carbon nanotubes (MWCNTs) array of about 40 nm in diameter and 500 to 1300 nm in length was directly grown on Au interdigitated electrodes by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD). The growth catalyst of Ni_3C-Ni at the tip of the MWCNTs array was observed by transmission electron microscope (TEM) and selected area electron diffraction (SAED). The sensing properties of MWCNTs arrays to NO_2, H_2S, CH_3SH and C_8H_10 were investigated at operating temperature from 100 to 250 oC. The resistance change to sulfur gases was higher than NO_2 and C_8H_10. It was suggested that Ni at the tip was sulfidized to be Ni_xS in sulfur gas and that the p-n junction was formed at the interface between p-type MWCNTs and n-type Ni_xS.

A polyoxovanadate-surfactant hybrid layered crystal was synthesized by using decyltrimethylammonium (C-10) cation. The hybrid crystal with a formula of (C-10)(4)[H2V10O28]center dot 8H(2)O (C-10-V-10) contained diprotonated decavanadate anions, which were connected to each other to form hydrogen-bonded cluster chains. Conductivity and photoreactivity of C-10-V-10 were also investigated.

Water-soluble titanium complexes are attractive titanium sources for solution synthesis of titanium-based materials using water as a solvent due to their high stability in aqueous solution in wide range of pH, and have been made from expensive metal titanium ultrafine powder. In this study, TiCl 4 and Ti(SO 4)2 that are inexpensive reagents than metal titanium fine powder were chosen as starting materials. TiC1 4 and Ti(SO 4) 2 were dropped into distilled water and large amount of NaOH solution was added here, then precipitates of Ti(OH) 4 were obtained. Then precipitates were washed with distilled water and dissolved into mixed solution of H 2O 2 and NH 3. And lactic acid as complexing agent was added to the solutions to obtain water-soluble titanium lactate complex solutions. These complex solutions generated no precipitate at pH O to 12 for 6 months. Yields of Ti in the both processes were 85% and removal ratios of Cl- and SO 4 2- ions were 99 and 93%, respectively. MCO 3 (M = Ca 2+, Sr 2+, Ba 2+) were dissolved in the complex solution prepared from TiC1 4, and the solution was dried and heated at 873 K for 5 h. Very fine and crystalline particles Of CaTiO 3, SrTiO 3 and BaTiO 3 were obtained by heating at 873 K in this solution method, while large particles Of CaTiO 3, SrTiO 3 and BaTiO 3 were obtained at 1273 K in solid-state reaction. Low temperature synthesis of titanium complex oxides by a new synthetic route of water-soluble titanium complex from titanium chloride and titanium sulfate as starting materials was successfully achieved.

We developed a new synthetic route of water-soluble complexes using TiCl4 and Ti(SO4)(2) as starting materials. The yield of Ti and the removal rate of the Cl- ion were over 85 and 98%, respectively. The lactato titanium complex solution obtained by this new synthetic route remained stable for more than 3 months without any precipitation. Single-phase CaTiO3, SrTiO3, and BaTiO3 were synthesized from the lactato titanium complex by heating at 873 K for 5 h. The nano-structured CaTiO3, SrTiO3, and BaTiO3 particle sizes were 50, 30, and 30 nm in diameter, respectively, and smaller than those obtained by the solid-state method. We have succeeded in the synthesis of very fine particles of CaTiO3, SrTiO3, and BaTiO3 at a temperature 400 K lower than that required for the solid-state method. (C)2011 The Ceramic Society of Japan. All rights reserved.

The metastable phase of TiO2(B), one of the polymorphs of titanium dioxide (TiO2), was prepared by a hydrothermal treatment of a titanium glycolate complex ([Ti-4(C2H2O3)(4)(C2H3O3)(2)(O-2)(4)O-2](6-)) at 473 K for 1-72 h in the presence of H2SO4. Characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the obtained samples were composed of single phase TiO2(B) and the particles had plate-like morphology. After post-synthetic hydrothermal crystal growth (PHCG) applied to the as-prepared sample, thicker plate-like shaped particles were obtained. The photocatalytic activities of the samples obtained by the hydrothermal treatment and after the subsequent PHCG were evaluated in terms of methanol decomposition. (C) 2009 The Ceramic Society of Japan. All rights reserved.

Titanium dioxide (TiO2(B), one of metastable polymorphs of TiO2 was prepared by hydrothermal reaction of glycolato peroxotitanium complex ([Ti-4(C2H2O3)(4)(C2H3O3)(2)(O-2)(2)](6) in the presence of H2SO4 as an additive. Characterization by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) revealed that the obtained powders were single-phase TiO2(B) with rod-like shape, Particle size and aspect ratio of TiO2(B) can be controlled by post-synthetic hydrothermal crystal growth (PHCG) of the as-prepared powder sample. (C) 2008 Elsevier B.V. All rights reserved.