Xiaohua Ju

Lithium amidoborane hydrazinates: synthesis, structure and hydrogen storage properties

The first metal amidoborane hydrazinate with a composition of LiNH2BH3·NH2NH2 was successfully synthesized and characterized in the present study. LiNH2BH3·NH2NH2 exhibits a monoclinic P21/n space group with lattice parameters of a = 10.0650 A, b = 6.3105 A, c = 7.4850 A, and β = 107.497°. Meanwhile, lithium amidoborane hydrazinates with different molar ratios of LiNH2BH3 (LiAB) and NH2NH2 were synthesized and characterized. It was found that 4LiAB–NH2NH2 can release 1.6 equiv. and 2.5 equiv. of H2/LiAB at 75 °C and 170 °C, respectively. Therefore, around 7.1 wt% and 11.1 wt% of hydrogen can be released from 4LiAB–NH2NH2 at 75 °C and 170 °C, respectively, which are higher values than those for pristine LiAB. A dehydrogenation mechanism, which may be initiated by the “homogeneous dissociation” of N–N in hydrazine, is also proposed and discussed in this study.

Lithiated Primary Amine—A New Material for Hydrogen Storage

A facile method for synthesizing crystalline lithiated amines by ball milling primary amines with LiH was developed. The lithiated amines exhibit an unprecedented endothermic dehydrogenation feature in the temperature range of 150-250 °C, which shows potential as a new type of hydrogen storage material. Structural analysis and mechanistic studies on lithiated ethylenediamine (Li2EDA) indicates that Li may mediate the dehydrogenation through an α,β-LiH elimination mechanism, creating a more energy favorable pathway for the selective H2 release.

Li2NH‐LiBH4, a complex hydride with near ambient hydrogen adsorption and fast‐lithium ion conduction

Complex hydrides have played important roles in energy storage area. Here a complex hydride made of Li2 NH and LiBH4 was synthesized, which has a structure tentatively indexed using an orthorhombic cell with a space group of Pna21 and lattice parameters of a=10.121, b=6.997, and c=11.457 Å. The Li2 NH-LiBH4 sample (in a molar ratio of 1:1) shows excellent hydrogenation kinetics, starting to absorb H2 at 310 K, which is more than 100 K lower than that of pristine Li2 NH. Furthermore, the Li+ ion conductivity of the Li2 NH-LiBH4 sample is about 1.0×10-5  S cm-1 at room temperature, and is higher than that of either Li2 NH or LiBH4 at 373 K. Those unique properties of the Li2 NH-LiBH4 complex render it a promising candidate for hydrogen storage and Li ion conduction.

Synthesis, Thermal Behavior, and Dehydrogenation Kinetics Study of Lithiated Ethylenediamine

The lithiation of ethylenediamine by LiH is a stepwise process to form the partially lithiated intermediates LiN(H)CH2 CH2 NH2 and [LiN(H)CH2 CH2 NH2 ][LiN(H)CH2 CH2 N(H)Li]2 prior to the formation of dilithiated ethylenediamine LiN(H)CH2 CH2 N(H)Li. A reversible phase transformation between the partial and dilithiated species was observed. One dimensional {Lin Nn } ladders and three-dimensional network structures were found in the crystal structures of LiN(H)CH2 CH2 NH2 and LiN(H)CH2 CH2 N(H)Li, respectively. LiN(H)CH2 CH2 N(H)Li undergoes dehydrogenation with an activation energy of 181±8 kJ mol(-1) , whereas the partially lithiated ethylenediamine compounds were polymerized and released ammonia at elevated temperatures. The dynamical dehydrogenation mechanism of the dilithiated ethylenediamine compounds was investigated by using the Johnson-Mehl-Avrami equation.