Superior low-temperature hydrogen release from the ball-milled NH3BH3–LiNH2–LiBH4 composite

In the present study, we employed a multi-component combination strategy to constitute an AB/LiNH2/LiBH4 composite system. Our study found that mechanically milling the AB/LiNH2/LiBH4 mixture in a 1:1:1 molar ratio resulted in the formation of LiNH2BH3 (LiAB) and new crystalline phase(s). A spectral study of the post-milled and the relevant samples suggests that the new phase(s) is likely ammoniate(s) with a formula of Li2−x(NH3)(NH2BH3)1−x(BH4) (0 < x < 1). The decomposition behaviors of the Li2−x(NH3)(NH2BH3)1−x(BH4)/xLiAB composite were examined using thermal analysis and volumetric method in a wide temperature range. It was found that the composite exhibited advantageous dehydrogenation properties over LiAB and LiAB·NH3 at moderate temperatures. For example, it can release ∼7.1 wt% H2 of purity at temperature as low as 60 °C, with both the dehydrogenation rate and extent far exceeding that of LiAB and LiAB·NH3. A selectively deuterated composite sample has been prepared and examined to gain insight into the dehydrogenation mechanism of the Li2−x(NH3)(NH2BH3)1−x(BH4)/xLiAB composite. It was found that the LiBH4 component does not participate in the dehydrogenation reaction at moderate temperatures, but plays a key role in strengthening the coordination of NH3. This is believed to be a major mechanistic reason for the favorable dehydrogenation property of the composite at moderate temperatures.

► A new ternary hydride composite, 1:1:1 AB/LiNH2/LiBH4, is created.
► This composite converts to Li2−x(NH3)(NH2BH3)1−x(BH4)/xLiAB by milling.
► The as-formed composite exhibits better DH rate and extent than LiAB and LiAB·NH3.
► The reaction sequence of H2 release from this composite is determined.
► The mechanism for the improvement of the DH properties is discussed.