Syntheses and hydrogen Desorption properties of metal-borohydrides M(BH4)n (M = Mg, Sc, Zr, Ti, and Zn; n=2-4) as advanced hydrogen storage materials

Metal-borchydrides M(BH4)(n) (M = Mg, Sc, Zr, Ti, and Zn; n = 2-4) were synthesized by mechanical milling process according to the following reaction; MCln + nLiBH(4)/nNaBH(4) -> M(BH4)(n) + nLiCl/nNaCl. Then the thermal desorption properties of M(BH4)(n) were investigated by gas-chromatography and mass-spectroscopy combined with thermogravimetry. The results indicate that the hydrogen desorption temperature T-d of M(BH4)(n) correlates with the Pauling electronegativity chi(P) of M; that is, T-d decreases with increasing value of chi(P). The components of desorbed gas for M = Mg, Sc, Zr and Ti (chi(P) <= 1.5) are hydrogen only, while that for M = Zn (chi(P) = 1.6) contains borane besides hydrogen. The Pauling electronegativity chi(P) of M is an indicator to estimate T-d of M(BH4)(n) as candidates for advanced hydrogen storage materials with high gravimetric hydrogen densities and low desorption temperatures.