The reactions in LiBH4-NaNH2 hydrogen storage system

Stepwise reactions were observed in the ball milling and heating process of the LiBH4-NaNH2 system by means of X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR). During the ball milling process, two concurrent reactions take place in the mixture: 3LiBH(4) + 4NaNH(2) -> Li3Na(NH2)(4) + 3NaBH(4) and LiBH4 + NaNH2 -> LiNH2 + NaBH4. The heating process from 50 degrees C to 400 degrees C is mainly the concurrent reactions of Li3Na(NH2)(4) + 3LiBn(4) -> 2Li(3)BN(2) + NaBH4 + 8H(2) and 2LiNH(2) + LiBH4 -> Li3BN2H8 -> Li3BN2 + 4H(2), where the intermediate phases Li3Na(NH2)(4) and LiNH2 serve as the reagents to decompose LiBH4. The merged equations for the mechanochemical and the heating reactions below 400 degrees C can be denoted as 3LiBH(4) + 2NaNH(2) -> Li3BN2 + 2NaBH(4) + 4H(2). The maximum dehydrogenation capacity in closed system below 400 degrees C is 5.1 wt.% H-2, which agrees well with the theoretical capacity (5.5 wt.% H-2) of the merged equation and thus demonstrates the suggested pathway. The subsequent step consists of the decompositions of NaBH4 and Li3Na(NH2)(4) within the temperature range of 400 degrees C-600 degrees C. The apparent activation energies of the two steps are 114.8 and 123.5 kJ/mol, respectively. They are all lower than that of our previously obtained bulk LiBH4. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.