LiBH4-Mg(BH4)2: A Physical Mixture of Metal Borohydrides as Hydrogen Storage Material

The LiBH4-Mg(BH4)(2) system has been investigated as a possible hydrogen storage material. Several composites were synthesized by ball milling, namely, xLiBH(4)-(1-x)Mg(BH4)(2) with x = 0, 0.10, 0.25, 0.33, 0,40, 0.50, 0.60, 0.66, 0.75, 0.80, 0.90, 1. The physical mixture was investigated by using X- ray powder diffraction and thermal analysis. Interestingly, already a small amount of LiBH4 makes the alpha to beta transition of Mg(BH4)(2) reversible, which has not been reported before. The eutectic composition was found to exist at 0.50 < x < 0.60 exhibiting a eutectic melting at 180 degrees C. A phase diagram was built based on the data obtained in this study. Furthermore, the decomposition of the material begins right after the melting; thus, the decomposition temperature of the composite is much lower than those of the pure borohydrides. At 270 degrees C the x = 0.50 composite releases about 7.0 wt % of hydrogen.