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The addition of transition metals to alkali intercalated fullerides proved to enhance their already good hydrogen absorption properties. Herein we present a study based on two different synthetic strategies, allowing the addition of nickel as aggregates with different size to the lithium fulleride Li6C60: the former is based on the metathesis of nickel chloride, while the latter on the thermal decomposition of nickel carbonyl clusters. The hydrogen-storage properties of the obtained materials have been investigated with manometric and calorimetric measurements, which indicated a clear enhancement of the final absorption value and kinetics with respect to pristine Li6C60, as a consequence of nickel surface catalytic activity towards hydrogen molecules dissociation. We found up to 10 % increase of the total H2 weight % absorbed (5.5 wt% H2) in presence of Ni aggregates. Furthermore, the control of the transition metal particles size distribution allowed reducing the hydrogen desorption enthalpy of the systems.

Lithium and hydrogen dynamics in Li12C60 and Li12C60Hy are investigated by means of 7Li and 1H solid state Nuclear Magnetic Resonance (NMR) in the temperature range 80–550 K. Differential scanning calorimetry characterization on the hydrogen sorption and X-rays structural analysis are also reported. In the pure phase, the 7Li results show a thermally activated dynamics that can be associated to Li motions within the crystal interstices. Upon hydrogenation, Li ionic motion is considerably hindered by the presence of hydrofullerene molecules. The 1H measurements show that C–H bonds are stable on the local scale up to 400–450 K. The NMR results at higher temperatures are compatible with a H diffusion mechanism which anticipates the H desorption process.

We report the extensive investigation of Li and H dynamics in Li6C60 and Li6C60Hy, by combining 7Li and 1H solid state NMR measurements with DC/AC conductivity, in order to evaluate the potential application of these systems for energy-storage purposes. 7Li NMR results show a local motion of Li ions above 200 K in both pristine and hydrogenated compounds, with activation energies of 90–150 meV and correlation times of about 30 ps. Evidences of Li interdiffusive dynamics are given by conductivity measurements in Li6C60 already above 120 K, with activation energies of 240 meV, suggesting that ionic conductivity is of the order of 10−5 S cm−1 at room temperature, with correlation times of about 150 ps. On the other hand, the Li6C60Hy behaves like a semiconductor with a high energy gap (ca. 2.5 eV), suggesting that diffusion of intercalated Li ions is prevented. 1H NMR measurements indicate the absence of H motions for the whole temperature range investigated (up to 360 K), neither on macroscopic or local scale. Li6C60 good properties for H2-storage are confirmed in terms of absorption capacity (5 wt% H2), moreover we found that around 35% of lithium segregates in LiH form, leaving Li4C60H40 as the final hydrogenation product.