Isolation and characterization of blackish-brown BY2-melanin accumulated in cultured tobacco BY-2 cells.

The tobacco BY-2 cell line is one of the most utilized plant cell lines. After long-term culture, the cells turn brown to black, but the causal pigment is unknown. We successfully isolated a blackish-brown pigment from BY-2 cells cultured for 3 weeks. Morphological and spectroscopic analyses indicated that the pigment had similar features to a melanin-like substance reported previously. Furthermore, physicochemical analyses revealed that this pigment possessed most of the properties of melanin-like pigments. In addition, the high nitrogen content suggested that it differed from common plant melanins classified as allomelanins, suggesting a novel eumelanin-like pigment: "BY2-melanin". This is the first example showing that eumelanin-like pigments are produced in the cultures of plant cells for which the accumulation of melanin has not been reported. This tobacco BY-2 cell culture technique may represent a customizable and sustainable alternative to conventional melanin production platforms, with significant potential for industrial and pharmacological applications.

Eutectic Phenomenon of LiNH2-KH Composite in MH-NH3 Hydrogen Storage System.

Hydrogenation of a lithium-potassium (double-cation) amide (LiK(NH2)2), which is generated as a product by ammonolysis of litium hydride and potassium hydride (LiH-KH) composite, is investigated in details. As a result, lithium amide (LiNH2) and KH are generated after hydrogenation at 160 °C as an intermediate. It is noteworthy that the mixture of LiH and KNH2 has a much lower melting point than that of the individual melting points of LiNH2 and KH, which is recognized as a eutectic phenomenon. The hydrogenation temperature of LiNH2 in the mixture is found to be significantly lower than that of LiNH2 itself. This improvement of reactivity must be due to kinetic modification, induced by the enhanced atomic mobility due to the eutectic interaction.

Catalytic modification in dehydrogenation properties of KSiH3.

A number of known catalysts, which have been proven to be very effective for several hydrogen species, were studied in order to determine their effects on the hydrogen ab/desorption properties of KSiH3. Among all the catalysts used in this work, mesoporous Nb2O5 is found to be quite effective, with a reduction in activation energy from 142 kJ mol(-1) for pristine KSi to 63 kJ mol(-1) for mesoporous-Nb2O5-added KSi, thus allowing desorption to start at 100-120 °C. Any disproportionation is not observed in the controlled hydrogenation process. The mechanism for this improvement is also proposed in detail. The kinetic modifications on the ab/desorption properties of KSiH3 provide an alternative to the well-known family of heavy BCC alloys which are capable of working in the same temperature range but with a lower gravimetric hydrogen content, almost half of the KSi system.

Trace Ammonia Equilibrium Pressure of Zirconium Phosphate in Moisture.

Zirconium phosphate-absorbed ammonia gas and the ammonia concentration (pressure) decreased to 2 ppm (ca. 20 Pa). However, it has not been clarified what the equilibrium pressure of zirconium phosphate is during ammonia gas ab/desorption. In this study, the equilibrium pressure of zirconium phosphate during ammonia ab/desorption was measured using cavity ring-down spectroscopy (CRDS). For ammonia-absorbed zirconium phosphate, a two-step equilibrium plateau pressure was observed during the ammonia desorption in gas. The value of the higher equilibrium plateau pressure at the desorption process was about 25 mPa at room temperature. If the standard entropy change (ΔS0) of the desorption process is assumed to be equal to the standard molar entropy of ammonia gas (192.77 J/mol(NH3)/K), the standard enthalpy change (ΔH0) is about -95 kJ/mol(NH3). In addition, we observed hysteresis in zirconium phosphate at different equilibrium pressures during ammonia desorption and absorption. Finally, the CRDS system allows the ammonia equilibrium pressure of a material in the presence of water vapor equilibrium pressure, which cannot be measured by the Sievert-type method.

Regeneration Process of Ammonia-Absorbed Zirconium Phosphate to Zirconium Phosphate.

Zirconium phosphate [Zr(HPO4)2·H2O] absorbs 2 mol(NH3)/mol[Zr(HPO4)2·H2O] with a low equilibrium plateau ammonia concentration of around 1 ppm in water. In this study, in order to investigate the regeneration process of ammonia-absorbed zirconium phosphate [Zr(NH4PO4)2·H2O], Zr(NH4PO4)2·H2O was heat-treated above 353 K under an inert gas. Then, the structures of the heat-treated samples were evaluated using powder X-ray diffraction and thermogravimetry-mass spectrometry measurements. Zr(NH4PO4)2·H2O started to desorb ammonia and the crystal water at 353 K. Then, Zr(NH4PO4)2·H2O was changed to the anhydrous monoammoniate [Zr(NH4PO4)(HPO4)] at 473 K and formed anhydrous zirconium phosphate [Zr(HPO4)2] at 673 K. The anhydrous zirconium phosphate and the anhydrous monoammoniate reabsorbed ammonia in ammonia water. Those initial absorption rates were small compared with Zr(HPO4)2·H2O. The slow kinetics of the anhydrous zirconium phosphate corresponded to the small interlayer distances. The ammonia concentration composition isotherms indicated that the anhydrous zirconium phosphate and anhydrous monoammoniate have a low ammonia equilibrium plateau concentration of around 1 ppm in ammonia water. Zr(NH4PO4)2·H2O is formed from Zr(NH4PO4)(HPO4) by the reabsorption of ammonia and water after 1-10 cycles. We found that zirconium phosphate is an ammonia remover which can be used repeatedly at 473 K.

Temperature rise of LaNi5-based alloys by hydrogen adsorption.

The temperature rise of AB5-type alloys by hydrogen adsorption was limited by their critical temperatures (Tc). We found the relation between the H2 desorption temperatures of metal hydrides at atmospheric pressure (Ts) and their Tc followed the Guldberg rule (Tc = 3/2 Ts), revealing a simple method to estimate Tc.

Analysis of sodium generation by sodium oxide decomposition on corrosion resistance materials: a new approach towards sodium redox water-splitting cycle.

In this study, the investigation of materials with corrosion resistance was carried out to prevent side reactions caused by sodium oxide (Na2O) in the Na-redox thermochemical water splitting cycle, and essential operational conditions for sodium (Na) generation from Na2O were also investigated. Thermal desorption spectroscopy and X-ray diffraction techniques at altered conditions were mainly used for the experimental investigation. Numerous types of materials were tested to find materials with high resistance towards corrosion and to understand essential thermal decomposition processes of Na2O. In addition, under different temperatures and pressure conditions, the thermodynamic calculation of Gibbs free energy was performed to obtain experimental results. As a result, a Ti alloy showed significant resistance towards the corrosive reaction by Na2O. The obtained experimental and simulated results support the direct decomposition of Na2O to form Na and O2 below 600 °C under low partial pressure conditions. The optimized conditions for Na generation with the Ti alloy sample can be used for low temperature water splitting.

Synergetic NH3 absorption properties of the NaBH4-LiBH4 mixed system.

NaBH4 does not absorb NH3 below 100 kPa but transforms into a liquid state after NH3 absorption. On the other hand, LiBH4 absorbs NH3 at pressures lower than 100 kPa. Interestingly, mixed borohydrides absorbed NH3 at low pressures and were liquefied above 100 kPa due to a synergetic phenomenon. The kinematic viscosity of the liquefied state was in situ analyzed during NH3 absorption.

Catalytic Activities of Various Niobium Oxides for Hydrogen Absorption/Desorption Reactions of Magnesium.

Five types of niobium(V) oxides (Nb2O5) were synthesized by hydrothermal and heat treatment processes, and their structural properties and catalytic activities for the hydrogen absorption/desorption reactions of magnesium were characterized. The synthesized Nb oxides were dispersed on magnesium hydride (MgH2), a typical hydrogen storage material, using the ball-milling method. All the synthesized Nb oxides improved the reaction kinetics of the hydrogen desorption/absorption reactions. The catalytic activities for the hydrogen desorption were comparable, while the hydrogen absorption rates were significantly different for each synthesized Nb oxide. This difference can be explained by the structural stability of Nb2O5, which is related to the formation of a catalytically active state by the reduction of Nb2O5 during the ball-milling process. Notably, the highest catalytic effect was observed for Nb2O5 with a highly crystalline pyrochlore structure and a low specific surface area, suggesting that pyrochlore Nb2O5 is a metastable phase. However, only the amorphous Nb oxide was out of order, even though there is a report on the high catalytic activity of amorphous Nb oxide. This is attributed to the initial condensed state of amorphous Nb oxide, because particle size affects the dispersion state on the MgH2 surface, which is also important for obtaining high catalytic activity. Thus, it is concluded that Nb2O5 with lower stability of the crystal structure and smaller particle size shows better catalysis for both hydrogen desorption and absorption reactions.

Concentration-composition-isotherm for the ammonia absorption process of zirconium phosphate.

The ammonia absorption process of zirconium phosphate has been studied using the concentration-composition-isotherm (CCI), X-ray diffraction and thermogravimetry-mass spectrometry (TG-MS). It was clarified that the equilibrium plateau concentration appeared due to two phase coexistence.

Effective Factor on Catalysis of Niobium Oxide for Magnesium.

Magnesium is a promising hydrogen storage material but requires an efficient catalyst to enhance the sluggish kinetics of its hydrogen desorption/absorption reactions. Niobium catalysts have been shown to accomplish this, but the effective factors for catalysis on hydrogen desorption/absorption of Mg are not well understood. In order to investigate these aspects, various types of Nb oxides were synthesized and mixed with Mg, and their catalytic properties were investigated. The spray pyrolysis synthesis of Nb oxides at different temperatures produced homogeneous spherical particles with different degrees of crystallinity, while Nb oxide particles synthesized by simple calcination of ammonium niobium oxalate were nonuniform. These Nb oxides show significant catalytic activities for the hydrogen desorption/absorption of Mg, with amorphous oxides being more effective catalyst precursors than crystalline precursors. Metastable, amorphous Nb oxide is more easily converted to the reduced state, which is the catalytically active state for the reactions. In addition, Nb in the deactivated sample is in the oxidized state compared with the initially activated sample, and the catalytically active (reduced) state is recovered by reactions with hydrogen. Based on these findings, it is concluded that the chemical state of Nb is an important factor in catalyzing the desorption/absorption of hydrogen by Mg, and the catalytically active state can be preserved without further treatments.

Surface modification effects of graphite for selective hydrogen absorption by titanium at room temperature.

Surface modification effects of graphite and organic solvents on Ti were investigated by thermogravimetry (TG), Raman spectroscopy, and transmission electron microscopy (TEM) observations to improve its hydrogen absorption properties. As a result, Ti ball-milled with graphite showed high reactivity and selectivity for hydrogen with high durability.

The reaction process of hydrogen absorption and desorption on the nanocomposite of hydrogenated graphite and lithium hydride.

The lithium-carbon-hydrogen (Li-C-H) system is composed of hydrogenated nanostructural graphite (C(nano)Hx) and lithium hydride (LiH). C(nano)Hx is synthesized by ball-milling of graphite under a hydrogen atmosphere. In this work, the reaction process of hydrogen absorption and desorption on the Li-C-H system is investigated. The C(nano)Hx-LiH composite can desorb about 5.0 mass% of hydrogen at 350 degrees C with the formation of Li2C2 until the second cycle. However, the hydrogen desorption amount significantly decreases from the third cycle. Furthermore, it is shown by using gas chromatography that a considerable amount of hydrocarbons is desorbed during the rehydrogenation process. These results indicate that the amount of reaction between the polarized C-H groups in C(nano)Hx and LiH is reduced due to a decrease in the C-H groups by losing carbon atoms under the hydrogen absorption and desorption cycles.

Operando spectroscopic analyses for the ammonia absorption process of sodium borohydride.

The ammonia absorption process of sodium borohydride for ammonia storage has been studied by using the operando NMR and FT-IR measurements under various ammonia pressures. As a result, the characteristic variation in the chemical states of both materials due to the liquefaction has been clarified.

MgH2-CoO: a conversion-type composite electrode for LiBH4-based all-solid-state lithium ion batteries.

Several studies have demonstrated that MgH2 is a promising conversion-type anode toward Li. A major obstacle is the reversible capacity during cycling. Electrochemical co-existence of a mixed metal hydride-oxide conversion type anode is demonstrated for lithium ion batteries using a solid-state electrolyte. 75MgH2·25CoO anodes are obtained from optimized mixing conditions avoiding reactions occurring during high-energy ball-milling. Electrochemical tests are carried out to investigate the cycling capability and reversibility of the on-going conversion reactions. The cycling led to formation of a single-plateau nanocomposite electrode with higher reversibility yield, lowered discharge-charge hysteresis and mitigated kinetic effect at high C-rate compared to MgH2 anodes. It is believed that reduced diffusion pathways and less polarized electrodes are the origin of the improved properties. The designed composite-electrode shows good preservation and suitability with LiBH4 solid electrolyte as revealed from electron microscopy analyses and X-ray photoelectron spectroscopy.

Bulk-Type All-Solid-State Lithium-Ion Batteries: Remarkable Performances of a Carbon Nanofiber-Supported MgH2 Composite Electrode.

Magnesium hydride, MgH2, a recently developed compound for lithium-ion batteries, is considered to be a promising conversion-type negative electrode material due to its high theoretical lithium storage capacity of over 2000 mA h g-1, suitable working potential, and relatively small volume expansion. Nevertheless, it suffers from unsatisfactory cyclability, poor reversibility, and slow kinetics in conventional nonaqueous electrolyte systems, which greatly limit the practical application of MgH2. In this work, a vapor-grown carbon nanofiber was used to enhance the electrical conductivity of MgH2 using LiBH4 as the solid-state electrolyte. It shows that a reversible capacity of over 1200 mA h g-1 with an average voltage of 0.5 V (vs Li/Li+) can be obtained after 50 cycles at a current density of 1000 mA g-1. In addition, the capacity of MgH2 retains over 1100 mA h g-1 at a high current density of 8000 mA g-1, which indicates the possibility of using MgH2 as a negative electrode material for high power and high capacity lithium-ion batteries in future practical applications. Moreover, the widely studied sulfide-based solid electrolyte was also used to assemble battery cells with MgH2 electrode in the same system, and the electrochemical performance was as good as that using LiBH4 electrolyte.

Nitrogen Dissociation via Reaction with Lithium Alloys.

Lithium alloys are synthesized by reactions between lithium metal and group 14 elements, such as carbon, silicon, germanium, and tin. The nitrogenation and denitrogenation properties are investigated by thermal and structural analyses. All alloys dissociate the nitrogen triple bond of gaseous molecules to form atomic state as nitrides below 500 °C, which is lower than those required for conventional thermochemical and catalytic processes on nitride syntheses. For all alloys except for germanium, it is indicated that nanosized lithium nitride is formed as the product. The denitrogenation (nitrogen desorption) reaction by lithium nitride and metals, which is an ideal opposite reaction of nitrogenation, occurs by heating up to 600 °C to form lithium alloys. Among them, the lithium-tin alloy is a potential material to control the dissociation and recombination of nitrogen below 500 °C by the reversible reaction with the largest amount of utilizable lithium in the alloy phase. The nitrogenation and denitrogenation reactions of the lithium alloys at lower temperature are realized by the high reactivity with nitrogen and mobility of lithium. The above reactions based on lithium alloys are adapted to the ammonia synthesis. As a result, ammonia can be synthesized below 500 °C under 0.5 MPa of pressure. Therefore, the reaction using lithium alloys is recognized as a pseudocatalyst for the ammonia synthesis.

Kinetic Modification on Hydrogen Desorption of Lithium Hydride and Magnesium Amide System.

Various synthesis and rehydrogenation processes of lithium hydride (LiH) and magnesium amide (Mg(NH2)2) system with 8:3 molar ratio are investigated to understand the kinetic factors and effectively utilize the essential hydrogen desorption properties. For the hydrogen desorption with a solid-solid reaction, it is expected that the kinetic properties become worse by the sintering and phase separation. In fact, it is experimentally found that the low crystalline size and the close contact of LiH and Mg(NH2)2 lead to the fast hydrogen desorption. To preserve the potential hydrogen desorption properties, thermochemical and mechanochemical rehydrogenation processes are investigated. Although the only thermochemical process results in slowing the reaction rate due to the crystallization, the ball-milling can recover the original hydrogen desorption properties. Furthermore, the mechanochemical process at 150 °C is useful as the rehydrogenation technique to preserve the suitable crystalline size and mixing state of the reactants. As a result, it is demonstrated that the 8LiH and 3Mg(NH2)2 system is recognized as the potential hydrogen storage material to desorb more than 5.5 mass% of H2 at 150 °C.

Metal hydride-based materials towards high performance negative electrodes for all-solid-state lithium-ion batteries.

Electrode performances of MgH2-LiBH4 composite materials for lithium-ion batteries have been studied using LiBH4 as the solid-state electrolyte, which shows a high reversible capacity of 1650 mA h g(-1) with an extremely low polarization of 0.05 V, durable cyclability and robust rate capability.

Anode properties of magnesium hydride catalyzed with niobium oxide for an all solid-state lithium-ion battery.

The anode properties of pristine MgH2 and MgH2 catalyzed with Nb2O5 have been investigated for an all solid-state lithium-ion battery. The catalytic effect stabilizes the plateau voltage as a result of kinetic improvement of the hydrogen transfer from the Mg phase to the Li phase.