Crystal face dependence of the decomposition activity of MnO_x-modified rutile-type TiO₂ on 2-naphthol in water in the dark was investigated. Clusters of MnO_x were modified onto (110) and (001) surfaces of rutile single crystals using chemisorption calcination cycle (CCC) processing. The major valences of Mn on (110) were Mn(III) and Mn(IV), whereas those on (001) were Mn(II) and Mn(III). Energy calculations for the MnO_x cluster on (110) corresponded to experimentally obtained results. Rutile nanorods with high (110) ratio were prepared using hydrothermal methods. Under the same conditions, MnO_x was impregnated on the surface using CCC processing. Despite smaller specific surface area and surface Mn concentration, the synthesized nanorod powder on 2-naphthol in water in the dark exhibited almost identical decomposition activity to that of a commercial rutile powder. The ratio of Mn(IV) of the nanorod powder was higher than that of the commercial rutile powder. The normalized activity for the nanorod powder was more than twice as much as that for commercial rutile powder. These results imply that the interface design between the base material and MnO_x clusters plays an important role in the decomposition activity of organic substances in the dark.

The phase transition of Sm₃NbO₇ with orthorhombic fluorite-related structure was investigated. Three kinds of solid solutions, Sm₃(Nb_1−xTa_x)O₇, (Sm_1−xNd_x)₃NbO₇, and (Sm_1−xEu_x)₃NbO₇ were prepared. Sm₃NbO₇ and Sm₃TaO₇ form complete solid solutions, and their structures are well described with the space group C222₁. The phase transition temperature for Sm₃(Nb_1−xTa_x)O₇ increases from 1080 K with increasing Ta concentration. Sm₃TaO₇ undergoes the phase transition when the temperature is increased through ca. 1340 K and above the transition temperature, its structure is well described with space group Pnma. The phase transition temperature for (Sm_1−xNd_x)₃NbO₇ decreases with Nd concentration. On the other hand, that for (Sm_1−xEu_x)₃NbO₇ increases with the ratio of Eu concentration. However, both of these solid solutions show the same trend, i.e., with decreasing the average rare earth size, the phase transition temperature of (Sm_1−xLn_x)₃NbO₇ (Ln = Nd, Eu) increases. This trend is the same as that for Ln₃MO₇ (M = Mo, Ru, Re, Os, or Ir). That is, the phase transition occurs with lattice contraction.

Catalytic combustion-type CO gas sensors employing the mixture of Pt-loaded CeO₂–ZrO₂–ZnO catalyst and artificial diamond with high thermal conductive nature were successfully fabricated. While the sensor employing only Pt-loaded CeO₂–ZrO₂–ZnO catalyst exhibited CO sensing performance over 100°C with high electrical noise, the sensor with the mixture of artificial diamond and the catalyst could operate even at 80°C and the electrical noise was also reduced. At the same operating temperature at 130°C at which both sensors showed the highest sensitivity, the 50% response time toward CO gas concentration change was accelerated from 103 s for the sensor without artificial diamond to 76 s by using the sensor with artificial diamond. Furthermore, the sensitivity toward CO gas was also increased.

Fast scintillation materials based on ternary halide mixed crystals, Rb_1−xCs_xCaCl₃ were synthesized. Broad luminescence bands were observed around 360 nm and can be ascribed to Auger-free Luminescence (AFL) for vacuum ultraviolet core-level excitation. Several luminescence bands for interband excitation were also observed. For X-ray excitation, the band that is ascribed to AFL could be clearly detected. The scintillation decay components due to the AFL had decay time constant of 0.8 ns for RbCaCl₃ and 2.0 ns for Rb_1−xCs_xCaCl₃ (x ≠ 0). CsCaCl₃ had the largest light yield of the AFL component, exceeding 1200 photons/MeV, which was slightly lower than that of BaF₂. The light yield of the AFL component increased linearly with Cs content.

Highly Br⁻ ion conducting solid electrolytes were developed by replacing La³⁺ ion site in LaOBr with lower valent Sr²⁺ and Ca²⁺ ions to form Br⁻ ion vacancies for Br⁻ ion conduction with suppressing the sample decomposition. By doping two kinds of divalent cations simultaneously into LaOBr lattice, high amount of Br⁻ ion vacancy was successfully introduced compared to the previously reported La_0.9Sr_0.1OBr_0.9. Among the samples prepared, the highest Br⁻ ion conductivity was obtained for the La_0.85Sr_0.10Ca_0.05OBr_0.85 solid, which was ca. 5 times higher than that of La_0.9Sr_0.1OBr_0.9.

The electrochemical cell consisting of a gadolinium-doped ceria porous electrolyte (GDC, Ce_0.9Gd_0.1O_1.95), Ni (20 and 30 vol %)–GDC bilayer cathode and Ru (20 and 30 vol %)–GDC bilayer anode was used for the dry-reforming of a real biogas with CO₂ or air using pulsed current (0.1, 1, 10, 100 Hz) under the applied voltage of 0.5 V. The composition of the supplied gas was adjusted to CH₄/CO₂ = 1/1 volume ratio in the dry-reforming with CO₂ at 800°C (CH₄+ CO₂ → 2H₂ + 2CO). The conversion ratios of the supplied CH₄ and CO₂ were 60.8–80.6 and 71.8–85.9%, respectively. The outlet gas contained 8.9–29.6 vol % H₂ gas. The increase in the frequency of the pulsed current decreased the formation rates of H₂ and CO gases. Carbon was deposited on the cathode by the disproportionation reaction of CO gas and the thermal decomposition of CH₄. When air was mixed with the biogas, stable reforming to produce H₂ and CO gases proceeded for 24 h at 700–800°C using pulsed current. The formation rates of H₂ and CO gases were independent of the frequency of the pulsed current. The oxygen gas of air reacted with the carbon deposited on the cathode and removed it as CO gas.

This paper reports the performance of a solid oxide fuel cell with yttria-stabilized zirconia (YSZ) electrolyte, Ni–YSZ anode and (La_0.8Sr_0.2)_0.95MnO₃ (LSM) cathode or RuO₂–YSZ cathode using air oxidant or a CO₂ oxidant and a H₂ fuel with 3% H₂O at 600–800°C. The power density was higher for air oxidant than for a CO₂ oxidant. The measured power density was associated with the reduction of CO₂ gas to solid carbon for the RuO₂–YSZ cathode. In the cell with the LSM cathode, a CO₂ oxidant was reduced to the mixed state of CO molecules and solid carbon. The reactivity of O₂ or CO₂ molecules in their mixed oxidant gas system for the YSZ cell with the LSM cathode changed drastically at 50–70 vol % CO₂ in the O₂–N₂–CO₂ gas system. It is possible to produce an electric power and to reduce CO₂ gas into solid carbon at the same time during the operation of a solid oxide fuel cells using a CO₂ oxidant.

Three types of Ag-doped potassium niobates, a layered K₄Nb₆O₁₇·nH₂O, a pyrochlore-type (K,H)NbO₃·nH₂O, and a perovskite-type KNbO₃, were synthesized via a hydrothermal reaction. The layered-type K₄Nb₆O₁₇·nH₂O was prepared at 240°C using KOH/Nb₂O₅ = 6; the pyrochlore-type compound was prepared at 220°C using KOH/Nb₂O₅ = 10; and the orthorhombic perovskite-type compound was prepared at 260°C using KOH/Nb₂O₅ = 40. Ag ions were intercalated to the interlayer of the layered compound and the tunnel of the pyrochlore-type compound, while Ag metal was loaded on the surface of the perovskite-type compound. The layered- and perovskite-type compounds exhibited photocatalytic activity for phenol degradation under ultraviolet light irradiation; however, the pyrochlore-type compound did not exhibit good photocatalytic activity.

Polybenzimidazole (PBI) electrolyte and TiO₂-doped PBI electrolyte membranes were fabricated for application in intermediate temperature hydrogen fuel cells. These membranes and their assembled cells were characterized by field emission scanning electron microscopy, optical microscope, conductivity measurement, and fuel cell evaluation. Metal oxide particles have a high affinity for phosphoric acid. Hence, TiO₂ was added to the PBI electrolyte membrane at various concentrations to increase the retention of phosphoric acid. The proton conductivity of the electrolyte membrane with TiO₂ nanoparticles and their influence on the fuel cell power generation characteristics were investigated under anhydrous condition at 150°C. The TiO₂/PBI electrolyte membrane achieved output characteristics more than twice that of the pure PBI electrolyte membrane. It was observed that the addition of TiO₂ improved the phosphate holding power of the electrolyte membrane. TiO₂/PBI membrane retained high conductivity values at the higher temperatures as a result of its high doping level and high water retention capacity. TiO₂ (2 wt %)/PBI composite membrane showed the best performance with a power density of 434 mW cm⁻². These results suggest that TiO₂/PBI-based composite membranes are promising electrolytes for intermediate temperature polymer electrolyte membrane fuel cells.

A solid oxide fuel cell with an yttria-stabilized zirconia (YSZ) electrolyte, Ni–YSZ anode and Ru–YSZ cathode was fabricated to measure the cell performance at 500–800°C using a H₂, CO or CO–H₂O fuel and air oxidant. The terminal voltage drop at a larger current density was due to the overpotential at the electrodes. A part of CO fuel was electrochemically oxidized to produce an electric power and some fractions of CO fuel were decomposed to form CO₂ gas and solid carbon (disproportionation reaction, 2CO → CO₂ + C). In the CO–H₂O fuel, electrochemical oxidation of a CO fuel, CO disproportionation, the water–gas shift reaction (CO + H₂O → H₂ + CO₂) and oxidation of deposited carbon (C + H₂O → H₂ + CO) proceeded in the anode. It is possible to produce an electric power and a H₂ fuel at the same time during the operation of a SOFC using a CO–H₂O fuel.

Titania nanotubes (TNTs) have nanometer-sized tubular morphologies with layered structures. TNTs are candidate sorbents for the removal of many heavy metals and radionuclides. In this study, we investigated the Cs⁺ sorption capacity of TNTs synthesized by a solution chemical method in comparison with those of zeolite and TiO₂ particles. The TNT powder was shaken in 0.2–4.0 mM CsCl aqueous solution at 10, 25, and 40°C for up to 7 days. The sorption tests showed that the sorption density of Cs⁺ per gram of TNT was lower than that of zeolite. TiO₂ did not show Cs⁺ adsorption. The sorption isotherm of Cs⁺ on TNTs was fitted with the Langmuir model. The sorption of Cs⁺ on zeolite was well described with the Freundlich model. The TNT structure was maintained after sorption testing regardless of the concentration of CsCl aqueous solution. Elemental analysis of the TNTs showed uniformly adsorbed Cs⁺ throughout the TNTs. Na⁺ was also detected in the TNTs both before and after sorption, but the residual Na⁺ concentration decreased with increasing the adsorbed Cs⁺ concentration. These results clearly showed that the Cs⁺ was intercalated into the layered structures of the TNTs by ion-exchange with Na⁺.

Layered titanates including transition metal in interlayer space were prepared by ion exchange process. Ammonia adsorption was performed into the transition metal-including layered titanates by aqueous liquid and gas phase. X-ray diffraction patterns of the sample with aqueous liquid and gas phase adsorption confirm that ammonia can be adsorbed without collapse of the titanate layered structure. Further, there was a large increase in the ammonia adsorption amount for the sample with gas phase adsorption comparing to that with the aqueous liquid phase adsorption. Such large amount of ammonia adsorption results from the elimination of the water molecules coordinated with the metal cation between the layers by preheating.

Electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) play an important role in renewable energy source technologies, typically including metal-air batteries, fuel cells and water splitting devices. Therefore, the development of bifunctional catalysts for OER and ORR is of great importance to enhance the performance of these devices. Herein, we present a Pr/Ba cation-disordered perovskite Pr_2/3Ba_1/3CoO_3−δ, as a novel bifunctional catalyst for OER and ORR. Here δ is the content of oxygen vacancies. Rietveld refinement of the X-ray powder diffraction data of Pr_2/3Ba_1/3CoO_2.98 was successfully performed by a single phase with an orthorhombic Pnma Pr/Ba cation-disordered perovskite-type structure. The bond valence sum of Co cation, 3.11 and thermogravimetric measurements suggested the coexistence of Co³⁺, Co⁴⁺, Pr³⁺ and Pr⁴⁺ cations in the bulk Pr_2/3Ba_1/3CoO_2.98. The X-ray photoemission spectroscopy of Pr_2/3Ba_1/3CoO_2.98 indicated the coexistence of these four cations at the sample surface, which would improve the electrocatalysis. The electrical conductivity σ of Pr/Ba cation-disordered perovskite Pr_2/3Ba_1/3CoO_3−δ was higher than that of Pr/Ba cation-ordered layered perovskite PrBaCo₂O_6−δ. The σ of Pr_2/3Ba_1/3CoO_3−δ and PrBaCo₂O_6−δ decreased with an increase of temperature. The concentration of oxygen vacancies δ of Pr_2/3Ba_1/3CoO_3−δ increased with increasing temperature. Electrochemical measurements of the Pr/Ba cation-disordered perovskite Pr_2/3Ba_1/3CoO_2.98 indicated higher OER and ORR catalytic activities, compared to the Pr/Ba cation-ordered layered perovskite PrBaCo₂O_6−δ. The Pr_2/3Ba_1/3CoO_2.98 exhibited higher bifunctional electrocatalytic activities compared with many bifunctional catalysts in the literature. These results highlight the Pr/Ba cation-disordered perovskite-type Pr_2/3Ba_1/3CoO_3−δ as a promising bifunctional catalyst for renewable energy applications.

The crystallization behavior of bismuth borate glass in hydrogen argon mixed atmosphere was examined. When the 70B₂O₃–30Bi₂O₃ glass prepared by the melt quenching method was heat treated in a 5% hydrogen-95% argon atmosphere, spherical bismuth metal particles were formed in the glass matrix at 380°C, which is higher than glass transition temperature at 336°C and close to crystallization temperature at 399°C. As increase of heat treatment temperature, the diameter of bismuth grain was increased. Electrochemical activity of bismuth metal containing glass-ceramics was also evaluated as a negative electrode in lithium ion battery. Suppression of irreversible capacity at initial cycle due to lithium insertion was successfully performed by reductive heat treatment for crystallization of bismuth metal into glass matrix.

The sulfide based electrolyte Li₃PS₄ was directly produced on the cathode active materials LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) using the SEED method which was a new liquid-phase process developed by applying liquid-phase shaking method. The generation of PS₄³⁻ unit in the SEED process was confirmed by in-situ Raman spectroscopy measurement. The generation of β-Li₃PS₄ on NMC was shown using X-ray elemental mapping, transmission electron microscope observation and electron diffraction analysis. An all-solid-state cell composed of [90NMC·10Li₃PS₄ by SEED composite | Li₃PS₄ | In] was fabricated. It showed promising charge–discharge cycle performance, which could be ascribed to good retention of electrochemical contact at the interface between NMC and the electrolyte during the cycling.

Control rods are one of the structural components in a nuclear reactor and are required to have a high functionality and reliability to provide a safe nuclear reactor. Random-oriented boron carbide (B₄C) is normally used as the control rods, but cracks are easily generated during the nuclear reaction because of volume swelling due to the accumulation of helium gas and nonhomogeneous thermal stress distribution during the neutron absorption reaction. In this study, we were able to control the crystalline orientation of the B₄C and align the tubal pores for controlling the thermal stress distribution and releasing the helium gas by controlling the dispersion of particles in a slurry and the rotation in a magnetic field.

The morphology and peeling behavior of poly(vinyl alcohol) (PVA) derivatives in water is investigated. The uneven surface is observed through the tapping mode of scanning probe microscopy; it originates from PVA molecules adsorbed on the solid surface. The force curve shows an extension, which results in PVA peeling. The extension agrees well with the worm-like chain model. The persistence length of all PVA derivatives used in this study approximates the 2 C–C bonds (0.31 nm). The distribution of the contour length is plotted for each molecule based on fifty peeling tests. It shows that the conformation of PVA derivatives adsorbed on the solid surface reflects that of PVA derivatives in an aqueous solvent. These results indicate that the slight difference of functional groups affects the flexibility of the molecule and the adsorption behavior onto the solid surface is different.

Pyrochlore-type A₂B₂O_7−z (A = Pb, Bi; B = Nb, Ru, Sn, Ir) oxide fine powders were synthesized by a wet-chemical method. The electrochemical reduction properties of carbon dioxide were investigated with carbon-based gas-diffusion-type electrodes loaded with various pyrochlore-type oxide catalysts. The current–voltage curves under pure CO₂ gas flow showed that the Sn-based pyrochlore-type oxides gave high electrocatalytic activities for the electrochemical CO₂ reduction. Among the pyrochlore-type oxides tested, Bi₂Sn₂O₇ showed the highest CO₂ reduction reaction which gave CO as a main product at very high concentration. XPS analyses showed that the high performance for the electrochemical CO₂ reduction of Bi₂Sn₂O₇ was come from the valence state of Sn and/or oxygen adsorption–desorption properties of the pyrochlore-type oxide.

A simple method was used to form one-dimensional (1D) TiO₂ nanorod arrays on the surfaces of hot-pressed Ti-dispersed Al₂O₃ composites by heating. After heating below 600°C, the Ti surface morphologies had changed significantly, while the Al₂O₃ surfaces remained unchanged. After heating for 5 h above 500°C, vertically grown nanorods were observed on the surfaces of Ti grains among Al₂O₃/Ti composites, which exhibited a crystalline phase of rutile-type TiO₂ doped with a small quantity of aluminum. Nanorod formation was believed to be due to Ti diffusion and its acceleration by Al incorporation. The photocatalytic activity of the heated Al₂O₃/Ti composites was verified by rhodamine B degradation under ultraviolet light irradiation, although the oxide fraction on the composites was small. The activity was enhanced by 1D TiO₂ nanorod growth on the composite surface.

This article provides the first critical review on the discovery and development of BaNdInO₄. Exploring a new structure family of ionic conductors is an important task to develop ceramic ionic conductors. Since some A₂BO₄ compositions exhibit high oxide-ion conductivities, we investigated ABCO₄ compositions to explore new oxide-ion conductors with A/B/C cation-ordered structures. Here A, B and C are cations [ionic radii: r(A) ≥ r(B) ≥ r(C)]. In 2014, we discovered a new material BaNdInO₄ which belongs to a new structure family of perovskite-related structures. This BaNdInO₄-type structure (monoclinic, P2₁/c) consists of alternative stacking of the A rare earth oxide unit and perovskite unit with a⁻ b⁻ c⁻ tilt system. We also discovered new materials BaRInO₄ (R = Sm, Y, Ho, Er, Yb) having the BaNdInO₄-type structure, and report their lattice parameters and anisotropic chemical expansion. Electrical conductivity of BaNdInO₄ was higher than those of BaRInO₄ (R = Sm, Y, Er). Oxide-ion conduction was dominant for BaNdInO₄ in the P(O₂) region from 3.8 × 10⁻²² to 5.5 × 10⁻⁹ atm at 858°C. Oxide-ion conductivities of Ba_1.1Nd_0.9InO_3.95, BaSr_0.1Nd_0.9InO_3.95 and BaCa_0.2Nd_0.8InO_3.9 were higher than that of BaNdInO₄. Structure analyses of Ba_1.1Nd_0.9InO_3.95 and BaSr_0.1Nd_0.9InO_3.95 indicated that the excess Ba and doped Sr cations were partially substituted for Nd cation and that there existed oxygen vacancies, leading to the increase of the carrier concentration and higher oxide-ion conductivity. Following the discovery of BaNdInO₄, BaRScO₄ (R = Nd, Eu, Y, Yb) and SrYbInO₄ were reported as new ABCO₄ materials. BaYScO₄ and BaYbScO₄ have the BaNdInO₄-type structure. BaNdScO₄ and BaEuScO₄ crystallize into the space group Cmcm, which has a higher symmetry than P2₁/c for BaNdInO₄. SrYbInO₄ is the first example of pure oxide-ion conductors with CaFe₂O₄-type structure. Further investigations of ABCO₄ compositions and BaNdInO₄ related materials will lead to development of materials science and solid state ionics.

Porous ceramic membranes have received increasing attention for decades. Due to their excellent thermal and chemical properties. Because their pore sizes of as-sintered silicon carbide supports are within the microfiltration range, silicon carbide membranes have been actively investigated by many researchers and industries. For example, silicon carbide supports by themselves (average pore size of 1–10 µm) and microfiltration layer-coated silicon carbide supports (average pore size of 0.1–1 µm) can be easily prepared. However, there is insufficient data concerning the combination of ultrafiltration layer-coated silicon carbide supports (average pore size of below 0.1 µm). Therefore, the authors first prepared typical microfiltration layer-coated silicon carbide supports, and then deposited ultrafiltration layers on them. Furthermore, the authors characterized the membrane properties of the ultrafiltration layer-coated silicon carbide supports. In addition, the possibility of reducing the average pore size of microfiltration layer-coated silicon carbide supports below 0.1 µm was investigated, and improving the water permeability of ultrafiltration layer-coated silicon carbide supports by controlling processing conditions such as the heat-treatment temperature, dip-coating conditions, and composition of the alumina coating slurry was explored.

Samaria-doped ceria, (SmO_1.5)_0.2(CeO₂)_0.8 (SDC), containing nickel (Ni) was prepared as the anode of solid oxide fuel cell fueled with 6% ammonia (NH₃). The Ni-free SDC powders prepared by the reverse co-precipitation method exhibited poor catalytic activities for NH₃ decomposition in 6% NH₃/Ar. Impregnation of Ni onto the SDC powders significantly enhanced its catalytic activity. The catalytic activity was highest at 10 wt % Ni–SDC, but it decreased with an increase in the Ni content. Contrary to expectation, the anodic performances were similar between 10 and 40 wt % of Ni loading and the highest maximum power densities were 98.8 and 96.5 mW·cm⁻² at 900°C, respectively. Impedance analysis of the anodes revealed that the anodic performance was rate-controlled by the similar process in 4%H₂ fuel and that was electrochemical oxidation and diffusion processes.