Reversibility of Al/Ti Modified LiBH4

Lithium borohydride has a high reversible hydrogen storage capacity. For its practical use as an on-board hydrogen storage medium in mobile applications, the temperature and pressure conditions along with the kinetics of the hydrogenation/dehydrogenation cycles have to be improved. Lithium borohydride can be modified by ball-milling with Al- and/or Ti-containing compounds. In this study, lithium alanate (LiAlH4), is used as an Al source. From careful examination of the ball-milled samples, it appears that LiBH4 remains unchanged during milling. The samples contain similar to 100 nm diameter Al and/or Al-Ti solid solution (ss) crystallites. When used alone, Ti has a limited effect whereas Al is shown to be active, lowering the temperature of decomposition and increasing the desorption rate and reversibility at moderate temperature and pressure (85 bar, 350 degrees C). During cycling, AlB2 is formed in the dehydrogenated state and disappears in the hydrogenated state; its formation increases the stability of the products and thus results in a lower desorption temperature. The Al-Ti (ss) also allows a slow release of hydrogen at very low temperatures (200 degrees C).