アルカリ金属アミド－水素系における熱力学及び動力学特性

広島大学(Hiroshima University)博士(学術)Doctor of Philosophydoctora

Synthesis, structural characterization, and hydrogen desorption properties of Na[Al(NH2BH3)4]

Na[Al(NH2BH3)4], a mixed-metal amidoborane, was synthesized by ball-milling (solid method) and the chemical reaction in THF (solution method). Solid method has a tendency to remain unreacted NaAlH4 and AB. In the solution method, the partial decomposition of Na[Al(NH2BH3)4] would proceed during mixing in THF. The local structural characterization of as-synthesized material was performed by MAS NMR and FT-IR. While Na[Al(NH2BH3)4] desorbed hydrogen in two steps as reported, the results of structural characterization suggested that the hydrogen desorption in the 2nd step would originate from the AlNBH phase. Effect of hydrogen pressure during ball-milling was also investigated for nNH3BH3NaAlH4 (n = 1, 4) composites. In the case of n = 4, Na[Al(NH2BH3)4] was formed under both Ar and H2 atmosphere. However, in the case of n = 1, Na[Al(NH2BH3)4] was only formed under H2 atmosphere, whereas most of H2 was desorbed during ball-milling under Ar atmosphere. Thus, the hydrogen pressure is necessary for the synthesis in the case of n = 1. Potential energy diagram of AB-NaAlH4 system was described

Simulation of direct coupling 20 kW class photovoltaic and electrolyzer system connected with lithium ion capacitors

The 20 kW class Proton Exchange Membrane (PEM) type Water Electrolyzer (Ely) system directly coupled with photovoltaic panels (PV) was developed. In this system the number of Ely cells is changeable during operation to truck maximum power point of the PV by adjusting operation voltage. Since neither DC/DC converters nor power conditioners are used in this system, there are no power conversion loss, however the input current into Ely fluctuates due to the fluctuation of the irradiation. Lithium ion capacitors (LiC) are incorporated into PV-Ely system in order to smooth the Ely input current, that would stabilize the pressure of generated hydrogen gas and extend the lifetime of the Ely cells. Before the examination using the facility, the simulation program for the 20 kW PV-ELY-LiC system was developed. The program can simulate the operation condition of the system each one second. The simulation program can be used to estimate the current smoothing effect by the LiC. The simulation program can also contribute to a preparatory experiment and tuning of parameters in the control program for the system

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

Lithium hydrazinidoborane: A polymorphic material with potential for chemical hydrogen storage

Herein, we describe the synthesis and characterization (chemical, structural, and thermal) of a new crystal phase of lithium hydrazinidoborane (LiN2H4BH3, LiHB), which is a new material for solid-state chemical hydrogen storage. We put in evidence that lithium hydrazinidoborane is a polymorphic material, with a stable low-temperature phase and a metastable high-temperature phase. The former is called β-LiHB and the latter α-LiHB. Results from DSC and XRD showed that the transition phase occurs at around 90 °C. On this basis, the crystal structure of the novel β-LiHB phase was solved. The potential of this material for solid-state chemical hydrogen storage was verified by TGA, DSC, and isothermal dehydrogenations. Upon the formation of the α-LiHB phase, the borane dehydrogenates. At 150 °C, it is able to generate 10 wt % of pure H 2 while a solid residue consisting of polymers with linear and cyclic units forms. Reaction mechanisms and formation of bis(lithium hydrazide) of diborane [(LiN2H3)2BH2] +[BH4]- as a reaction intermediate are tentatively proposed to highlight the decomposition of β-LiHB in our conditions. © 2014 American Chemical Society

Lithium Hydrazinidoborane: A Polymorphic Material with Potential for Chemical Hydrogen Storage

Herein, we describe the synthesis and characterization (chemical, structural, and thermal) of a new crystal phase of lithium hydrazinidoborane (LiN₂H₄­BH₃, LiHB), which is a new material for solid-state chemical hydrogen storage. We put in evidence that lithium hydrazinidoborane is a polymorphic material, with a stable low-temperature phase and a metastable high-temperature phase. The former is called β-LiHB and the latter α-LiHB. Results from DSC and XRD showed that the transition phase occurs at around 90 °C. On this basis, the crystal structure of the novel β-LiHB phase was solved. The potential of this material for solid-state chemical hydrogen storage was verified by TGA, DSC, and isothermal dehydrogenations. Upon the formation of the α-LiHB phase, the borane dehydrogenates. At 150 °C, it is able to generate 10 wt % of pure H₂ while a solid residue consisting of polymers with linear and cyclic units forms. Reaction mechanisms and formation of bis­(lithium hydrazide) of diborane [(LiN₂H₃)₂­BH₂]⁺­[BH₄]⁻ as a reaction intermediate are tentatively proposed to highlight the decomposition of β-LiHB in our conditions