Reversibility of Al/Ti Modified LiBH4

Lithium borohydride has a high reversible hydrogen storage capacity. For its practical use as an onboard 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 ∼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 °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 °C).