Experimental Evidence of Ca[B12H12] Formation During Decomposition of a Ca(BH4)2 + MgH2 Based Reactive Hydride Composite

Abstract

The combination of Ca(BH4)2 and MgH2 materials results in a composite with remarkable hydrogen storage properties. However, full reversibility upon the (re)hydrogenation reaction has not yet been achieved. The poor reversibility is shown to be linked to the formation of stable intermediate phases or side products upon decomposition. In this work, we show, for the first time, the clear experimental evidence of CaB12H12 among the decomposition products of a Ca(BH4)2 + MgH2 composite. A combination of 11B Magic Angle Spinning–Nuclear Magnetic Resonance (11B{1H} MAS NMR), ex situ X-ray diffraction (XRD) and Rietveld analysis are presented. An assessment of the (de)hydrogenation and (re)hydrogenation reactions of Ca(BH4)2 + MgH2 composite is reported. The experimental results provided in this work highlight the reasons for the limited reversibility observed in the Ca(BH4)2 + MgH2 composite upon (re)hydrogenation.