Size-Dependent Kinetic Enhancement in Hydrogen Absorption and Desorption of the Li−Mg−N−H System

Abstract

High operating temperature and slow kinetics retard the practical applications of the Li-Mg-N-H system for hydrogen storage. To alleviate these problems, a first attempt was carried out by synthesizing Li(2)MgN(2)H(2) through sintering a mixture of Mg(NH(2))(2)-2LiNH(2) and investigating its size-dependent hydrogen storage performance. A dramatically enhanced kinetics for hydrogen absorption/desorption was achieved with a reduction in the particle size. For the dehydrogenation reaction, a three-dimensional diffusion-controlled kinetic mechanism was identified for the first time by analyzing isothermal hydrogen desorption curves with a linear plot method. The experimental improvement and mechanistic understanding on the dehydrogenation kinetics of the Li-Mg-N-H system shed light on how to further decrease the operating temperature and enhance the hydrogen absorption/desorption rate of the amide/hydride combined materials.

Affects of Mechanical Milling and Metal Oxide Additives on Sorption Kinetics of 1:1 LiNH2/MgH2 Mixture

“…The broad peak seen in the lower angle region is attributed to the kapton film used to prevent oxidation of the samples during measurement. The pattern of the Spex milled sample did reveal peak broadening and lower intensity indicating a decrease in particle size and an increase in defects [29]. Using the Scherrer equation to determine particle size from XRD patterns, the average MgH 2 particle was reduced from 35.3 nm to 23.6 nm.…”

Hydrogen Storage Properties of the Mg(NH<SUB>3</SUB>)<SUB>6</SUB>Cl<SUB>2</SUB>-LiH Combined System

“…It is well known that the typical N-H vibrations of Li 2 NH and Li 2 Mg(NH) 2 are at 3163 and 3174 cm À1 , respectively. 15,37) As a result, it can be believed that two phases of Li 2 NH and Li 2 Mg(NH) 2 are involved in the solid residues after dehydrogenated at 310 C. According to dehydrogenation measurements and structural analyses, we can give a picture of the chemical process in heating process of the Mg(NH 3 ) 6 Cl 2 -18LiH combined system. As described above, the starting sample of Mg(NH 3 ) 6 Cl 2 -18LiH converts to the mixture of Mg(NH 2 ) 2 -4LiNH 2 -2LiCl-12LiH after 24 h of milling.…”

“…1) In contrast to the compressed hydrogen and the liquefaction hydrogen, hydrogen storage in the solid state is the most promising alternative. [2][3][4][5] In the past decades, the complex hydrides consisting of light elements, e.g., alanates, [6][7][8][9][10] amides, [11][12][13][14][15] borohydrides [16][17][18][19][20] and ammonia borane (AB), [21][22][23] have been attracting extensive attention as the potential hydrogen storage materials due to their high gravimetric and volumetric hydrogen storage densities. In particular, significant efforts have been made in recent years with metal amide-hydride combined systems since Chen et al reported that lithium nitride, Li 3 N could absorb/desorb reversibly 11.4 mass% of hydrogen in 2002.…”

“…11) A variety of metal amide-hydride combinations have been designed and developed for their hydrogen storage performances. [11][12][13][14][15] However, most of them still suffer from the high operating temperature for practical applications.…”

“…[11][12][13][14][15][26][27][28] Yamamoto et al found that NH 3 could react with alkali metal hydrides MH (M = Li, Na, and K) in an exothermic nature to release hydrogen (H 2 ) at room temperature. 26) Moreover, an ultrafast reaction was reported for NH 3 and LiH at above 300 C, which is in the order of microsecond.…”