Reactive Vapor-Phase Additives toward Destabilizing γ-Mg(BH 4 ) 2 for Improved Hydrogen Release

High Resolution Image Download MS PowerPoint Slide Magnesium borohydride (Mg(BH 4 ) 2 ) is a promising candidate for material-based hydrogen storage due to its high hydrogen gravimetric/volumetric capacities and potential for dehydrogenation reversibility. Currently, slow dehydrogenation kinetics and the formation of intermediate polyboranes deter its application in clean energy technologies. In this study, a novel approach for modifying the physicochemical properties of Mg(BH 4 ) 2 is described, which involves the addition of reactive molecules in the vapor phase. This process enables the investigation of a new class of additive molecules for material-based hydrogen storage. The effects of four molecules (BBr 3, Al 2 (CH 3 ) 6, TiCl 4, and N 2 H 4 ) with varying degrees of electrophilicity are examined to infer how the chemical reactivity can be used to tune the additive–Mg(BH 4 ) 2 interaction and optimize the release of hydrogen at lower temperatures. Control over the amounts of additive exposure to Mg(BH 4 ) 2 is shown to prevent degradation of the bulk γ-Mg(BH 4 ) 2 crystal structure and loss of hydrogen capacity. Trimethylaluminum provides the most encouraging results on Mg(BH 4 ) 2, maintaining 97% of the starting theoretical Mg(BH 4 ) 2 hydrogen content and demonstrating hydrogen release at 115 °C. These results firmly establish the efficacy of this approach toward controlling the properties of Mg(BH 4 ) 2 and provide a new path forward for additive-based modification of hydrogen storage materials.