Synthesis and Characterization of a Lithium-Doped Fullerane (Li_x-C₆₀-H_y) for Reversible Hydrogen Storage

Abstract

Herein, we present a lithium-doped fullerane (Li(x)-C(60)-H(y)) that is capable of reversibly storing hydrogen through chemisorption at elevated temperatures and pressures. This system is unique in that hydrogen is closely associated with lithium and carbon upon rehydrogenation of the material and that the weight percent of H(2) stored in the material is intimately linked to the stoichiometric ratio of Li:C(60) in the material. Characterization of the material (IR, Raman, UV-vis, XRD, LDI-TOF-MS, and NMR) indicates that a lithium-doped fullerane is formed upon rehydrogenation in which the active hydrogen storage material is similar to a hydrogenated fullerene. Under optimized conditions, a lithium-doped fullerane with a Li:C(60) mole ratio of 6:1 can reversibly desorb up to 5 wt % H(2) with an onset temperature of ~270 °C, which is significantly less than the desorption temperature of hydrogenated fullerenes (C(60)H(x)) and pure lithium hydride (decomposition temperature 500-600 and 670 °C respectively). However, our Li(x)-C(60)-H(y) system does not suffer from the same drawbacks as typical hydrogenated fullerenes (high desorption T and release of hydrocarbons) because the fullerene cage remains mostly intact and is only slightly modified during multiple hydrogen desorption/absorption cycles. We also observed a reversible phase transition of C(60) in the material from face-centered cubic to body-centered cubic at high levels of hydrogenation.

Hydrogen storage mechanism and lithium dynamics in Li12C60 investigated by μSR

“…This fraction increases if temperature is lowered, indicating that the reaction between C 60 and atomic hydrogen occurs with a very low energy barrier. This observation clarified that the relatively high temperatures (T > 373 K) needed to start the H 2 absorption [7,8] are then required only to activate the H 2 dissociation process operated by the alkali cluster.…”

“…Unfortunately, the existence of such superulleroids systems in the solid-state has never been confirmed, mainly due to the marked tendency of metals towards clusterization [6]. Nonetheless, the intercalation of lithium and sodium at high extent in fullerene host lattice leads to the formation of alkali-cluster intercalated fullerides, which indeed proved to reversibly uptake rather high amount of hydrogen via a complex chemisorption mechanism [7][8][9][10]. In these systems, the number of intercalated ions equals or exceeds the six-fold degeneracy of the t 1u -LUMO of C 60 .…”

Complex and liquid hydrides for energy storage

“…Reversible intercalation of Li or Na into the carbon can occur, stabilizing the metal phase and hence lowering the equilibrium decomposition temperature, for instance, that of NaH under 1 bar H 2 pressure from 425 to 225°C [154,171]. Also, lithium-and Nadoped fullerenes are capable of reversibly storing 5 wt% hydrogen [172,173].…”

Solid State Physicochemical Properties and Applications of Organic and Metallo- Organic Fullerene Derivatives

“…Hydrogen storage is achieved by heating the Li x C 60 material to between 200 and 350 °C under an applied H 2 pressure between 25 and 100 bars. Hydrogen storage of 5% in weight is achieved by applying °C, and the hydrogen release shows an onset at 270 °C in thermogravimetry-residual gas analysis experiments [239].…”

“…On the other hand, it has been recently shown [239] that a alkali-organic fullerene derivative, of average chemical formula Li x C 60 H y with x close to 6, can be used as active material for reversible hydrogen storage. The material, which displays an average charge transfer of six electrons to the C 60 cages and the spectral signature of partial selfpolymerization (possibly related to the presence of a minority polymeric Li 4 C 60 phase [126,136]), is able to undergo reversible hydrogenation to Li 6 C 60 H 40 , withy = 40 covalently linked hydrogens.…”