Hydrogen sites and dynamics in light-weight hydrogen-storage material magnesium-scandium hydride investigated with 1H and 2H NMR

Magnesium transition-metal alloys are a novel class of light-weight hydrogen-storage materials. We have studied magnesium-scandium hydride with magic-angle-spinning H-1 and H-2 NMR. A new double-quantum NMR method with Sc-45 recoupling reveals two types of deuterium with and without scandium neighbors. Their relative occurrence quantified with H-2-{Sc-45} TRAPDOR NMR reflects a non-statistical Mg and Sc distribution over the crystal lattice. The deuteron exchange observed with two-dimensional NMR is consistent with Mg and Sc-rich sub-nanometer clusters. Deuterium motion is governed by a broad range of energy barriers without clear correlation to the underlying chemical heterogeneity. (C) 2008 Elsevier B.V. All rights reserved.