Porous and Dense Magnesium Borohydride Frameworks: Synthesis, Stability, and Reversible Absorption of Guest Species

摘要

Hydrogen has been suggested as a carrier of renewable energy in future sustainable energy systems. However, the lack of safe, compact, and efficient storage of hydrogen remains an obstacle. In the solid state, hydrogen can be stored covalently bonded to a light element, for example, in complex ions BH4~- and NH2~-, or physisorbed in molecular form in a nanoporous material such as a metal-organic framework. Herein we report the first light-metal hydride capable of storing molecular hydrogen. This new form of magnesium borohydride has a large permanent porosity and can also reversibly adsorb nitrogen and small molecules such as dichloromethane. We report the synthesis, stability, transformations, and structure of two new polymorphs y- and 6-Mg(BH4)2 along with the first gas absorption experiments on porous Y-Mg(BH4)2. Our work shows that metal borohydrides and coordination polymers can have similar properties and anticipate the existence of novel hybrid materials.