Synthesis and hydrogen storage characteristics of Mg–B–H compounds by a gas–solid reaction

Magnesium borohydride [Mg(BH4)2] is an attractive complex hydride for hydrogen storage. In this study, attempts to synthesize Mg(BH4)2 were carried out by a solid–gas reaction through MgH2 and B2H6 in the absence of a liquid medium. The source of B2H6 was obtained by heating a mixture of NaBH4 and ZnCl2. The profile of pressure versus temperature indicated that the absorption kinetics of B2H6 by MgH2 were slow. Structural analysis confirmed the formation of Mg–B–H compounds. The reaction products presented two-step hydrogen release during heating. A small amount of hydrogen could be released from the as-synthesized Mg–B–H compounds at a low temperature of 215 °C. The slow reaction kinetics were significantly affected by the surface conditions of the MgH2 powders.

► It reveals the reaction mechanism of NaBH4 with ZnCl2.
► It presents an in situ method to synthesize complex hydride at moderate conditions.
► The study confirms the possibility of reaction between MgH2 and B2H6.