Thermal dehydrogenation behaviors and mechanisms of Mg(BH4)2∙6NH3-xLiH combination systems

• A novel Mg(BH4)2⋅6NH3-xLiH combination system is prepared.
• The onset dehydrogenation temperature of the LiH-contained samples is only 80 °C.
• The Mg(BH4)2⋅6NH3-6LiH composite releases 14.3 wt% hydrogen below 340 °C.
• The dehydrogenated Mg(BH4)2⋅6NH3-6LiH sample at 210 °C absorbs 2.2 wt% hydrogen.

A reactive composite of Mg(BH4)2⋅6NH3-xLiH is prepared, and the effects of the LiH content on the dehydrogenation/hydrogenation properties of the material are investigated. The results show that the presence of LiH with x = 3 reduces the onset dehydrogenation temperature of Mg(BH4)2⋅6NH3 from 130 °C to 80 °C in TPD mode. Approximately 14.3 wt% hydrogen is released from the Mg(BH4)2⋅6NH3-6LiH composite with distinctly reduced ammonia evolution while heating to 340 °C. Upon heating, Mg(BH4)2⋅6NH3 first reacts with LiH to form Mg(NH2)2, Li3BN2H8 and LiBH4 with the release of H2 and the evolution of a minor amount of NH3. The newly formed Mg(NH2)2 then reacts with LiH to produce H2 and Li2Mg(NH)2. Further elevating the operating temperature induces chemical reactions between Li2Mg(NH)2, LiBH4 and Li3BN2H8, causing the release of additional H2 and production of Li3BN2, LiMgBN2 and LiH. The dehydrogenated sample at 210 °C absorbs 2.2 wt% of hydrogen, exhibiting partial reversibility for hydrogen storage.