Novel catalytic effects of fullerene for LiBH4 hydrogen uptake and release.

The addition of catalysts to complex hydrides is aimed at enhancing the hydrogen absorption desorption properties. Here we show that the addition of carbon nanostructure C60 to LiBH4 has a remarkable catalytic effect, enhancing the uptake and release of hydrogen. A fullerene-LiBH4 composite demonstrates catalytic properties with not only lowered hydrogen desorption temperatures but also regenerative rehydrogenation at a relatively low temperature of 350 degrees C. This catalytic effect probably originates from C60 interfering with the charge transfer from Li to the BH4 moiety, resulting in a minimized ionic bond between Li+ and BH4(-), and a weakened covalent bond between B and H. Interaction of LiBH4 with an electronegative substrate such as carbon fullerene affects the ability of Li to donate its charge to BH4, consequently weakening the B-H bond and causing hydrogen to desorb at lower temperatures as well as facilitating the absorption of H2. Degradation of cycling capacity is observed and is probably due to the formation of diboranes or other irreversible intermediates.