Metal‐Borohydride‐Modified Zr(BH4)4⋅8 NH3: Low‐Temperature Dehydrogenation Yielding Highly Pure Hydrogen

Due to its high hydrogen density (14.8 wt %) and low dehydrogenation peak temperature (130 °C), Zr(BH4)4⋅8 NH3 is considered to be one of the most promising hydrogen-storage materials. To further decrease its dehydrogenation temperature and suppress its ammonia release, a strategy of introducing LiBH4 and Mg(BH4)2 was applied to this system. Zr(BH4)4⋅8 NH3–4 LiBH4 and Zr(BH4)4⋅8 NH3–2 Mg(BH4)2 composites showed main dehydrogenation peaks centered at 81 and 106 °C as well as high hydrogen purities of 99.3 and 99.8 mol % H2, respectively. Isothermal measurements showed that 6.6 wt % (within 60 min) and 5.5 wt % (within 360 min) of hydrogen were released at 100 °C from Zr(BH4)4⋅8 NH3–4 LiBH4 and Zr(BH4)4⋅8 NH3–2 Mg(BH4)2, respectively. The lower dehydrogenation temperatures and improved hydrogen purities could be attributed to the formation of the diammoniate of diborane for Zr(BH4)4⋅8 NH3–4 LiBH4, and the partial transfer of NH3 groups from Zr(BH4)4⋅8 NH3 to Mg(BH4)2 for Zr(BH4)4⋅8 NH3–2 Mg(BH4)2, which result in balanced numbers of BH4 and NH3 groups and a more active Hδ+⋅⋅⋅−δH interaction. These advanced dehydrogenation properties make these two composites promising candidates as hydrogen-storage materials.