Characterization of MnO2 positive electrode for Fuel Cell/Battery (FCB)

The use of manganese dioxide (MnO₂) as a positive electrode material in Fuel Cell/Battery (FCB) systems is described. A positive electrode containing MnO₂ was fabricated and its performance was evaluated for charge/discharge behavior in three different systems: (i) secondary battery positive electrode, (ii) positive electrode in an alkaline fuel cell, and (iii) positive electrode performance in an FCB system by performing half cell tests. MnO₂ was observed to possess redox capabilities as the positive electrode of a secondary battery when it was subject to charge/discharge cycles. It was found that Mn₃O₄, which inhibits the discharge reaction, was produced during charge/discharge cycles. The I–V characteristics of MnO₂ material were measured to check the feasibility of the fuel cell system by supplying H₂ into the negative electrode and O₂ into the MnO₂ positive electrode, respectively. The MnO₂ electrode showed similar performance to Ni electrode, which was fabricated by using a similar method to the MnO₂ electrode. The MnO₂ electrode also showed that it functioned as an FCB positive electrode, which was confirmed by continued production of current when the O₂ supply was terminated. These results suggest that MnO₂ is a good candidate for an FCB positive electrode material.     

Development of non-flammable lithium secondary battery with room-temperature ionic liquid electrolyte: Performance of electroplated Al film negative electrode

The negative electrode performance of the electroplated Al film electrode in the LiCl saturated AlCl₃–1-ethyl-3-methylimizadolium chloride (EMIC) + SOCl₂ melt as the electrolyte for use in non-flammable lithium secondary batteries was evaluated. In the cyclic voltammogram of the electroplated Al film electrode in the melt, the oxidation and reduction waves corresponding to the electrochemical insertion/extraction reactions of the Li⁺ ion were observed at 0–0.80 V vs. Li⁺/Li, which suggested that the electroplated Al film electrode operated well in the electrolyte. The almost flat potential profiles at about 0.40 V vs. Li⁺/Li on discharging were shown. The discharge capacity and charge–discharge efficiency was 236 mAh g⁻¹ and 79.2% for the 1st cycle and it maintained 232 mAh g⁻¹ and 77.9% after the 10th cycle. In addition, the initial charge–discharge efficiencies of the electroplated Al film electrode were higher than that of carbon electrodes. The main cathodic polarization reaction was the insertion of Li⁺ ions, and side reactions hardly occurred due to the decomposition reaction of the melt because the Li content corresponding to the electricity was almost totally inserted into the film after charging.     

Characterization of heme-coordinating histidyl residues of an engineered six-coordinated myoglobin mutant based on the reactivity with diethylpyrocarbonate, mass spectrometry, and electron paramagnetic resonance spectroscopy

A genetically engineered porcine myoglobin triple mutant (H64V/V68H/H93A) (VHA-Mb) contains 6 non-axial His residues (His24, His36, His48, His81, His82, and His119) besides two candidate axial His residues (His68 and His97). Although previous resonance Raman study on the ferric VHA-Mb were not conclusive for its coordination structure, present EPR parameters of the ferric VHA-Mb were consistent with bis-imidazole coordination of His68/His97. We further investigated the reactivity of these possible His ligands with diethylpyrocarbonate (DEPC) to clarify the coordination structure and their protonation states in ferric form. We found that the non-axial His residues were easily modified with a low concentration of DEPC based on UV spectral changes and MALDI-TOF-MS analyses. On the other hand, the two candidate axial His ligands were protected from the modification due to a limited steric exposure of their imidazoles to solvent, the Fe(3+)-N(epsilon2) coordination bond, and the protonation of N(delta1) by forming a hydrogen bond with their immediate surroundings. However, once N-carbethoxylation occurred at N(epsilon2) of His97, resulting in a disruption of the heme Fe(3+)-N(epsilon2) coordination bond, it facilitated the second N-carbethoxylation to take place at N(delta1) of the same imidazole ring, leading to a bis-N-carbethoxylated derivative and further to a ring-opened derivative. These phenomena were consistent with the bis-His68/His97 coordination. Further, these were not observed at all for cytochrome b(561), a transmembrane di-heme containing protein responsible for the ascorbate-specific transmembrane electron transfer, where only a specific N(delta1)-carbethoxylation of axial His occurred at a low concentration of DEPC, leading to an inhibition of the electron acceptance from ascorbate without a release of the heme. These distinct results might be related to a specific physiological mechanism being operative at the cytosolic heme center of cytochrome b(561).     

π-Conjugated polymer/GaN Schottky solar cells

We developed heterojunction-based Schottky solar cells consisting of π-conjugated polymers and n-type GaN. Poly (3,4-ethylendioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) was used as the transparent Schottky contact material and their electrical properties were investigated in comparison with those of a polyaniline (PANI) Schottky contact. The PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample exhibited high-quality rectifying characteristics with a low reverse leakage current of less than 10⁻⁸ A/cm² at a reverse bias voltage of −3 V. While investigating the photovoltaic performance, it was observed that the open-circuit voltage of the PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample reached 0.8 V, which was much superior to the photovoltage reported for a conventional metal/GaN Schottky photodetector. We also confirmed that the PEDOT:PSS is as promising a material as PANI for π-conjugated polymer/GaN Schottky solar cells.     

Electrochemistry of LiMn2O4 epitaxial films deposited on various single crystal substrates

LiMn₂O₄ epitaxial thin films were synthesized on SrTiO₃:Nb(1 1 1) and Al₂O₃(0 0 1) single crystal substrates by pulsed laser deposition (PLD) method and the electrochemical properties were discussed comparing with that of amorphous LiMn₂O₄ film on polycrystalline Au substrate. LiMn₂O₄ epitaxial film showed only a single plateau in charge–discharge curves and a single redox peak at the corresponding voltage of cyclic voltammograms. This phenomenon seems to originate from the effect of the epitaxy: the film is directly connected with the substrate by the chemical bond and this connection would suppress the phase transition of Li_xMn₂O₄ film during lithium (de-)intercalation. The discharge voltage of LiMn₂O₄ epitaxial film on SrTiO₃ was lower than that of LiMn₂O₄ film on Al₂O₃. This lowered discharge voltage may be caused by the electronic interaction between LiMn₂O₄ film and SrTiO₃:Nb n-type semiconductor substrate.     

Double-walled reformer tubes using high-temperature thermal storage of molten-salt/MgO composite for solar cavity-type reformer

Composite materials with alkali carbonate and magnesia have been examined for high-temperature thermal storage in solar tubular reformers. The concept of a double-walled reactor tube involves packing a molten-salt/ceramic composite material into the annular region between internal catalyst tube and exterior solar-absorber wall. In this paper, the shape and interior structure of the reactor tube are newly designed for use in solar cavity-type reformers using straight reactor tubes. Na₂CO₃, K₂CO₃, and Li₂CO₃ composite materials with magnesia were tested as thermal storage media for CO₂ reforming of methane during cooling mode of the reactor tube at a laboratory scale. The efficiency of Na₂CO₃/MgO composite with various MgO contents was also estimated. Composite materials of Na₂CO₃ 80–90 wt% and MgO 20–10 wt% were successfully delayed the cooling of the catalyst bed and sustained methane conversion at >90%. A solar cavity-type reformer consisting of multiple straight reactor tubes is expected to enable stable operation of the solar reforming process under fluctuating solar insolation during cloud passage.     

Preparation and fluorescence property of red-emitting Eu-activated amorphous calcium silicate phosphor

This paper describes the energy efficient synthesis of a red-emitting Eu³⁺-activated amorphous calcium silicate phosphor produced by heating a Eu³⁺-activated calcium silicate hydrate phosphor. Concentration quenching of the Eu³⁺-activated calcium silicate hydrate phosphor was not observed and the emission intensity did not decrease up to a Eu/(Ca+Eu) atomic ratio of 0.46. Heating of the Eu³⁺-activated calcium silicate hydrate (Eu/(Ca+Eu) atomic ratio = 0.32) phosphor produced an amorphous Eu³⁺-activated calcium silicate phosphor, which had a maximum emission intensity at 870 °C and emitted in the red under near-ultraviolet irradiation (395 nm). The emission intensity of the Eu³⁺-activated amorphous calcium silicate phosphor was about half that of a commercial BaMgAl₁₀O₁₇:Eu²⁺ phosphor, and shows great potential for application in white light-emitting diodes.     

Thermocapillary Convection and Buoyant-Thermocapillary Convection in the Annular Pools of Silicon Melt and Silicone Oil

The thermocapillary convection and buoyant-thermocapillary convection in the annular pool of silicon melt (Pr=0.011) and silicone oil (Pr=6.7) with depth d=10 mm differentially heated at the outer wall and cooled at the inner wall are investigated by 2-D numerical simulation. The numerical results exhibit that the thermocapillary flow is enhanced by buoyancy force for silicon melt while it is weakened for silicone oil. Linear stability analysis indicates that the buoyancy force destabilizes the thermocapillary convection, which is different from that for silicone oil. The detailed reason of different influence of buoyancy force on the thermocapillary flow with different Pr numbers is explained according to present numerical results.     

Correction of the thermal neutron capture cross section of 241Am obtained by the Westcott convention

There is large discrepancy among the reported experimental data of the thermal neutron capture cross section of ²⁴¹Am, where the activation measurements provided larger cross sections than those in the time-of-flight ones. The Westcott convention has been widely used for the derivation of the thermal neutron capture cross section in the activation measurements. We have estimated that this large discrepancy is due to the existence of the resonances below the cadmium cut-off energy (E_Cd ～ 0.5 eV). By reviewing the Westcott convention, we developed the correction method taking account of the contribution of the resonances near or below E_Cd. The correction term was evaluated using the JENDL-4.0. Application of the present method successfully improved the existing discrepancy of the thermal capture cross section of ²⁴¹Am.     

Visual color matching under various viewing conditions

In this article, we provide colorimetry data for which it was judged that the colors between different media matched under various viewing conditions. Painted color patches, a monitor, and printed color patches were used in the color matching experiments, in which we compared the appearances of the painted color patch and the monitor, or the monitor and the printed color patch, using the method of constant stimuli. The nine types of viewing conditions we used could be envisaged to occur when comparing different device outputs indoors. The experimental data obtained were compared with corresponding colors predicted with the use of five types of color appearance model, including color appearance formulae. We found that when the viewing conditions were the same for the different media, there was good agreement between the experimental data and the CIECAT94 model. And by adjusting the brightness induction and the chromatic induction factors, it was possible to improve conformity for the lightness and the chromaticity. Moreover, it was possible to improve the white point shift, which cannot be adjusted with the use of optimized parameters by introducing incomplete adaptation. By optimizing the parameters and introducing incomplete adaptation, it is possible to make the mean color difference ΔE between the corresponding color and the color matching point less than 10 CIELAB units for all of the viewing conditions.