Syntheses and Hydrogen Desorption Properties of Metal-Borohydrides M(BH 4 ) n

Abstract

Metal-borohydrides M(BH 4 ) n (M ¼ Mg, Sc, Zr, Ti, and Zn; n ¼ 2{4) were synthesized by mechanical milling process according to the following reaction; MCl n þ nLiBH 4 /nNaBH 4 ! M(BH 4 ) n þ nLiCl/nNaCl. Then the thermal desorption properties of M(BH 4 ) n were investigated by gas-chromatography and mass-spectroscopy combined with thermogravimetry. The results indicate that the hydrogen desorption temperature T d of M(BH 4 ) n correlates with the Pauling electronegativity P of M; that is, T d decreases with increasing value of P . The components of desorbed gas for M ¼ Mg, Sc, Zr and Ti ( P 5 1:5) are hydrogen only, while that for M ¼ Zn ( P ¼ 1:6) contains borane besides hydrogen. The Pauling electronegativity P of M is an indicator to estimate T d of M(BH 4 ) n as candidates for advanced hydrogen storage materials with high gravimetric hydrogen densities and low desorption temperatures