Tessui Nakagawa

Regeneration of Ammonia Borane Spent Fuel by Direct Reaction with Hydrazine and Liquid Ammonia

A method to regenerate lightweight, hydrogen-rich ammonia borane improves its prospects as a vehicular fuel source. Ammonia borane (H3N-BH3, AB) is a lightweight material containing a high density of hydrogen (H2) that can be readily liberated for use in fuel cell–powered applications. However, in the absence of a straightforward, efficient method for regenerating AB from dehydrogenated polymeric spent fuel, its full potential as a viable H2 storage material will not be realized. We demonstrate that the spent fuel type derived from the removal of greater than two equivalents of H2 per molecule of AB (i.e., polyborazylene, PB) can be converted back to AB nearly quantitatively by 24-hour treatment with hydrazine (N2H4) in liquid ammonia (NH3) at 40°C in a sealed pressure vessel.

Potassium(I) amidotrihydroborate: structure and hydrogen release.

Potassium(I) amidotrihydroborate (KNH(2)BH(3)) is a newly developed potential hydrogen storage material representing a completely different structural motif within the alkali metal amidotrihydroborate group. Evolution of 6.5 wt % hydrogen starting at temperatures as low as 80 degrees C is observed and shows a significant change in the hydrogen release profile, as compared to the corresponding lithium and sodium compounds. Here we describe the synthesis, structure, and hydrogen release characteristics of KNH(2)BH(3).

Improved Hydrogen Release from Ammonia–Borane with ZIF-8

The promotion for hydrogen release from ammonia-borane (AB) was observed in the presence of ZIF-8. Even at concentrations of ZIF-8 as low as 0.25 mol %, a reduction of the onset temperature for dehydrogenation accompanies an increase in both the rate and amount of hydrogen released from AB.

Physical, structural, and dehydrogenation properties of ammonia borane in ionic liquids

Ionic liquids (ILs) are excellent solvents for the dehydrogenation of ammonia borane (AB); however, the basic properties that allow efficient dehydrogenation are still unclear. In this report, density, viscosity, melting/freezing/glass transition temperature, solubility, and the dehydrogenation properties, including impurity gas quantification, of AB-imidazolium-based IL solutions were studied. Note that ILs can solubilize 32–35 wt% of AB, and the liquid AB–IL solutions have densities of ∼0.9 g cm−3, viscosities similar to motor oil (100–250 cP), and glass transition temperatures below −50 °C. AB–ILs are stable at room temperature for several weeks with minimal hydrogen generation, although some hydrolysis occurs immediately upon mixing as a result of trace water content. Between 80 and 130 °C, more than 2 mol H2/AB are desorbed from AB–ILs with limited impurity emissions. Furthermore, there is no reaction between AB and ILs upon dehydrogenation, and structural analysis reveals a complex solid solution.

Divalent State in YbGaGe: Magnetic, Thermal, Transport and Structural Studies

YbGaGe was reported as the first example of a material with zero thermal expansion that is accomplished by the temperature-variant Yb 2+ /Yb 3+ configuration [Salvador et al. : Nature 425 (2003) 702]. Here we report magnetic, transport, X-ray diffraction and thermal expansion measurements of single-crystal samples. The results reveal a stable divalent state of Yb ions in YbGaGe and a distinct volume-thermal contraction with decreasing temperature.