Abstract
Through the substitution of Li with Na in Li6C60, we synthesized a series of mixed alkali cluster intercalated fullerides, NaxLi6-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.
Highlights
Carbon nanostructures are often considered as ideal light and porous materials for the storage of gases, due to the high surface areas achievable
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 molÀ1 H2 for x = 1
Even a small substitution of Li with Na seems to be enough to overcome this structural change, which we recently recognized as a kinetics limiting process in Li6C60.24 It is worth highlighting the detection of peaks at the Bragg angle expected for LiH in x = 0 and 0.5, a quantitative estimation can not be done from XRD data, due to the unknown structure of the hydrofullerene anion and the low scattering factor of Li and H
Summary
Carbon nanostructures are often considered as ideal light and porous materials for the storage of gases, due to the high surface areas achievable. 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 molÀ1 H2 for x = 1.
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