Dehydrogenation reactions of 2NaBH4+MgH2 system

Reactive Hydride Composites (RHCs), ball-milled composites of two or more different hydrides, are suggested as an alternative for solid state hydrogen storage. In this work, dehydrogenation of 2NaBH4 þ MgH2 system under vacuum was investigated using complementary characterization techniques. At first, thermal programmed desorption of as-milled composite and single compounds was used to identify the temperature range of hydrogen release. RHC samples annealed at various temperatures up to 500 C were characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. It was found that the dehydrogenation reaction under vacuum is likely to proceed as follows: 2NaBH4 þ MgH2 (>250 C) / 2NaBH4 þ 1/2MgH2 þ 1/2Mg þ 1/2H2 (>350 C) 4 3/2NaBH4 þ 1/4MgB2 þ 1/2NaH þ 3/4Mg þ 7/4H2 (>450 C) / 2Na þ B þ 1/2Mg þ 1/2MgB2 þ 5H2. In addition, presence of NaMgH3 phase suggests the occurrence of secondary reactions.