Hydrogen-release mechanisms in LiNH2BH3·NH3BH3: A theoretical study

•The intermediate LiNHBH2·NH2BH2 is obtained by the loss of two molar equiv of H2 through the pathway A at 373 K.•The intermediate LiNH2BHNHBH3 is obtained by the loss of two molar equiv of H2 through the pathway B at 373 K.•At 501 K, the predominant final product LiNBNBH is given most likely through the pathway A.•The formation of LiH and a series of redox reactions are involved in the whole reaction.

The molecular mechanism of the dehydrogenation of LiNH2BH3·NH3BH3 to form [LiN2B2H] by the loss of five molar equiv of H2 at two consecutive temperatures of 373 K and 501 K has been investigated using computational quantum chemistry methods (B3LYP, MP2 and CCSD(T) methods). The intermediate LiNHBH2·NH2BH2 can be obtained through the pathway A at 373 K, in which LiH structures are formed by the transfer of hydridic H− from NH2BH3− to Li+ followed by the redox reactions of Hδ+ and Hδ− to form two molar equiv of H2. The intermediate LiNH2BHNHBH3 can also be generated via the pathway B at 373 K, in which a new NB bond forms and two equiv of H2 are released by the redox reactions. At 501 K, the predominant final product P1 (LiNBNBH) is given most likely through the formation of LiH and a series of redox reactions with the loss of three molar equiv of H2 in the pathway A. Meanwhile, the products P2 (LiNBBNH) and P3 [Li(NBBN)H] may be also obtained by the dehydrogenation via a sequence of redox reactions of Hδ+ and Hδ− to release three equiv of H2 at the temperature of 501 K. The present study would be helpful for experimental chemists to design better hydrogen-storage media.

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