Processing analysis of the ternary LiNH2-MgH2-LiBH4 system for hydrogen storage

In this article, we investigate the ternary LiNH2-MgH2-LiBH4 hydrogen storage system by adopting various processing reaction pathways. The stoichiometric ratio of LiNH2:MgH2:LiBH4 is kept constant with a 2:1:1 molar ratio. All samples are prepared using solid-state mechano-chemical synthesis with a constant rotational speed, but with varying milling duration. Furthermore, the order of addition of parent compounds as well as the crystallite size of MgH2 are varied before milling. All samples are intimate mixtures of Li-B-N-H quaternary hydride phase with MgH2, as evidenced by XRD and FTIR measurements. It is found that the samples with MgH2 crystallite sizes of approximately 10 nm exhibit lower initial hydrogen release at a temperature of 150 degrees C. Furthermore, it is observed that the crystallite size of Li-B-N-H has a significant effect on the amount of hydrogen release with an optimum size of 28 nm. The as-synthesized hydrides exhibit two main hydrogen release temperatures, one around 160 degrees C and the other around 300 degrees C. The main hydrogen release temperature is reduced from 310 degrees C to 270 degrees C, while hydrogen is first reversibly released at temperatures as low as 150 degrees C with a total hydrogen capacity of similar to 6 wt.%. Detailed thermal, capacity, structural and microstructural properties are discussed and correlated with the activation energies of these materials. (c) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.