On the reversible hydrogen storage in Mg(BH4)2 under moderate conditions

Mg(BH4)2 contains 14.9 mass% of hydrogen and is considered as a promising hydrogen storage material. Reversible hydrogen sorption under moderate conditions represents a main challenge for Mg(BH4)2 being utilized for solid-state hydrogen storage. Here, we achieve the reversible storage of 4.0 mass% of hydrogen at 265°C in Mg(BH4)2. That is, desorption of 7.5 mass% H at 265°C under vacuum and absorption of 4.0 mass% at 265°C and 160 bar H2. 11B MAS NMR measurements indicate that the reversible hydrogen sorption involves the formation of a decisive intermediate which shows a major resonance with a chemical shift at -50.0 ppm. The phase evolution in the hydrogen cycles as well as the capacity loss in the hydrogen sorption cycles is discussed.