Optimal hydrogen storage in sodium substituted lithium fullerides.

Through the substitution of Li with Na in Li6 C60 , we synthesized a series of mixed alkali cluster intercalated fullerides, Nax Li6-x C60 . These compounds share lattices of Na6 C60 and Li6 C60 with a cubic parameter linearly dependent on x. H2 absorption and desorption were studied by means of charge/discharge kinetic measurements and coupled calorimetric-manometric evaluation. By varying the stoichiometry, we found the best compromise among the absorption rate, temperature and amount of hydrogen for x = 0.5 and 1. Small concentrations of Na substituted to Li significantly lower the absorption temperature of Li6 C60 , improving the hydrogenation capacity, the kinetics, and the dehydrogenation enthalpy, the latter being 43.8 kJ mol-1 H2 for x = 1. This study moves further toward the utilization of intercalated fullerides for hydrogen storage applications.