Hydrogen storage properties and mechanisms of a Mg(BH4)2•2NH3-NaAlH4 combination system

The Mg(BH4)(2)center dot 2NH(3-x)NaAlH(4) (x = 0-4) combination systems were prepared by ball milling, and the reversible hydrogen storage behavior and its mechanisms were investigated and discussed. Combining NaAlH4 with Mg(BH4)(2)center dot 2NH(3) significantly reduces the operating dehydrogenation temperatures and effectively suppresses the emission of NH3 byproducts. The dehydrogenation onset temperature of the Mg(BH4)(2)center dot 2NH(3)-2NaAlH(4) system is lowered to ca. 70 degrees C, which is much lower than the onset temperatures of either Mg(BH4)(2)center dot 2NH(3) or NaAlH4. In addition, ammonia emission from Mg(BH4)(2)center dot 2NH(3) is thoroughly suppressed by the addition of NaAlH4, leading to approximately 11.3 wt% hydrogen released upon heating to 570 degrees C. Further investigations revealed that at the initial heating stage, Mg(BH4)(2)center dot 2NH(3) first reacts with NaAlH4 to produce NaBH4, Al3Mg2, Mg, Al0.95Mg0.05, BN, Na and AIN along with the release of hydrogen. Further increasing the operation temperature gives rise to a chemical reaction between NaBH4, AIN and Mg that liberates all of the hydrogen and yields the resultant products of MgAlB4, BN, Na and Al3Mg2. The dehydrogenated products can take up similar to 3.5 wt% of hydrogen at 450 degrees C and 100 bar of hydrogen pressure, exhibiting a partial reversibility for hydrogen storage. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.