Recent applications of Raman spectroscopy to the study of complex hydrides for hydrogen storage

Raman spectroscopy has been shown to be a powerful and versatile technique for the characterization of certain hydrogen storage materials. It has been used to investigate the local bonding environments of a range of borohydride compounds, contributing towards the interpretation of diffraction data for the determination of crystal structures: alkali metal (Li, Na, K, Rb, Cs); alkaline earth (Mg and Ca); and transition-metal (Zn and Mn). Raman has also been used to help identify phases (particularly amorphous) within decomposed borohydride compounds: CaB6 in decomposed Ca(BH4)2; MgB2 in decomposed Mg(BH4)2; and Li2B12H12 and boron in decomposed LiBH4. In situ Raman measurements on LiBH4 heated under Ar have shown the orthorhombic to hexagonal phase change, fusion, followed by the formation of Li2B12H12 and boron, as a function of temperature. The Raman vibrational modes for a range of candidate hydrogen storage materials – including borohydrides, ammonia borane, and magnesium hydride – have been tabulated. The data is from the literature and from recent measurements at the University of Birmingham.