Isotopic Exchange in Porous and Dense Magnesium Borohydride.

Angewandte Chemie (International ed. in English)

PubMedID: 26178701

Zavorotynska O, Deledda S, Li G, Matsuo M, Orimo SI, Hauback BC. Isotopic Exchange in Porous and Dense Magnesium Borohydride. Angew Chem Int Ed Engl. 2015;.
Magnesium borohydride (Mg(BH4 )2 ) is one of the most promising complex hydrides presently studied for energy-related applications. Many of its properties depend on the stability of the BH4 (-) anion. The BH4 (-) stability was investigated with respect to H?D exchange. In situ Raman measurements on high-surface-area porous Mg(BH4 )2 in 0. 3 MPa D2 have shown that the isotopic exchange at appreciable rates occurs already at 373 K. This is the lowest exchange temperature observed in stable borohydrides. Gas-solid isotopic exchange follows the BH4 (-) +D(. ) ?BH3 D(-) +H(. ) mechanism at least at the initial reaction steps. Ex situ deuteration of porous Mg(BH4 )2 and its dense-phase polymorph indicates that the intrinsic porosity of the hydride is the key behind the high isotopic exchange rates. It implies that the solid-state H(D) diffusion is considerably slower than the gas-solid H?D exchange reaction at the surface and it is a rate-limiting steps for hydrogen desorption and absorption in Mg(BH4 )2.