title: Isotopic Exchange in Porous and Dense Magnesium Borohydride.
abstract: 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˙ →BH3D(-) +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.
authors.affiliation: Department of Physics, Institute for Energy Technology, P.O.Box 40, 2027 Kjeller (Norway).
authors.forename: Olena
authors.initials: O
authors.lastname: Zavorotynska
authors.affiliation: Department of Physics, Institute for Energy Technology, P.O.Box 40, 2027 Kjeller (Norway).
authors.forename: Stefano
authors.initials: S
authors.lastname: Deledda
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan).
authors.forename: Guanqiao
authors.initials: G
authors.lastname: Li
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan).
authors.forename: Motoaki
authors.initials: M
authors.lastname: Matsuo
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan).|WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan).
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Orimo
authors.affiliation: Department of Physics, Institute for Energy Technology, P.O.Box 40, 2027 Kjeller (Norway). bjorn.hauback@ife.no.
authors.forename: Bjørn C
authors.initials: BC
authors.lastname: Hauback
keywords: Raman spectroscopy; gas-solid exchange; hydrogen isotope exchange; magnesium borohydride