Reversible dehydrogenation of Mg(BH4)2–LiH composite under moderate conditions

The Mg(BH4)2-xLiH (0.1 ≤ x ≤ 0.8) composites which exhibit favorable dehydrogenation and encouraging reversibility are experimentally investigated. LiH additive reduces the onset temperature for dehydrogenation to 150 °C. And hydrogen release exceeds 10 wt.% from the new binary material below 250 °C. Furthermore, rehydrogenation results show that 3.6 wt.% hydrogen can still be recharged after twenty cycles at 180 °C. It should be emphasized that the long-term reversibility of borohydride under 200 °C is long overdue. TPD, PCT, and high-pressure DSC measurements are used to characterize the improvements in thermodynamic and kinetic ways. In addition, FT-IR and NMR studies indicate that the composite has a significant synergistic effect during (de)hydrogenation processes. This work suggests that controlled cation stoichiometry combined with doping by metal Li+ subvalent to Mg2+ facilitate the formation of polyborane intermediates [B3H8]− and [B2H6]2−. They improve the dehydrogenation properties and make the material reversible under mild conditions.

Graphical abstractLiH additive reduces the onset temperature for dehydrogenation to 150 °C. And hydrogen release exceed 10 wt.% below 240 °C. Furthermore, 3.6 wt.% hydrogen can be recharged after twenty cycles at 180 °C. Controlled cation stoichiometry combined with doping by metal Li+ subvalent to Mg2+ facilitates the formation of polyborane intermediates [B3H8]− and [B2H6]2−.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Mg(BH4)2–LiH composite shows favorable dehydrogenation and proper reversibility. ► The dehydrogenation starts at 150 °C, with over 10 wt % H2 release. ► The reversible amount of hydrogen is 3.6 wt % after twenty cycles at 180 °C. ► Enthalpy and activation energy changes indicate the lattice aberrance. ► Controlled substitution facilitates the formation of polyborane intermediates.