Optimal hydrogen storage in sodium substituted lithium fullerides

Through the substitution of Li with Na in Li₆C₆₀, we synthesized a series of mixed alkali cluster intercalated fullerides, Na_xLi_6-xC₆₀. These compounds share lattices of Na₆C₆₀ and Li₆C₆₀ 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 Li₆C₆₀, 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.