Optimal hydrogen storage in sodium substituted lithium fullerides

Abstract

Through the substitution of Li with Na in LiC, we synthesized a series of mixed alkali cluster intercalated fullerides, NaLiC. These compounds share lattices of NaC and LiC with a cubic parameter linearly dependent on x. H 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 LiC, improving the hydrogenation capacity, the kinetics, and the dehydrogenation enthalpy, the latter being 43.8 kJ mol H for x = 1. This study moves further toward the utilization of intercalated fullerides for hydrogen storage applications.

Synthesis and characterization of mixed sodium and lithium fullerides for hydrogen storage

“…Data were analysed by means of Le Bail pat- tern decomposition using the fcc cell of C 60 . Similar to the parent low-stoichiometric compounds Na x Li 6−x C 60 , we expect a disordered occupation of Na and Li sites, as well as the presence of rotational disorder for C 60 molecules 10,12 . The emergence of the 400 peak intensity at around 25.4 • with the increase of x suggests a higher occupancy of Na in the 4b ( 1 2 , 1 2 , 1 2 ) and 8c ( 1 4 , 1 4 , 1 4 ) sites, rather than in the 32f (x,x,x) positions.…”

“…H 2 sorption. The H 2 sorption study on the Na x Li 6−x C 60 family has been recently reported 10 . In these compounds (i.e.…”

“…Recently, we managed to find an optimal sorption performance by synthesizing mixed Na and Li doped fullerides with composition Na x Li 6−x C 60 . These phases have demonstrated better performance with respect to Li 6 C 60 for x <2, reaching a full absorption at 553 K and 100 bar H 2 , with 44 kJ/mol H 2 desorption enthalpy 10 . With this paper, we extend the study of the Na-Li mixed phases for the high-stoichiometric compounds Na x Li 12−x C 60 , hereby reporting on the synthesis, structure, Raman spectroscopy, hydrogen sorption analysis, and muon spectroscopy of these novel fullerides.…”

Stability and Phase Formation in the (Li/Na)6C60–H Systems Studied by Neutron Scattering

“…ratio) forms a multiphase sample with various crystalline NaxC60 structures rather than the phasepure cubic Na6C60 fulleride, as previously reported. 15,17,22,30 On the other hand, similar to earlier studies, the diffraction data of Na743 do not show presence of unreacted NaD and/or metallic Na, and thus suggesting a complete intercalation of Na into the fullerene structure. 20,25,27 The deuterium-containing samples (Na523_D and Na623_D) reveal differences, when compared to the D-free powder.…”

“…1-9 More recently, light metal-based systems, in particular Li-and Na-incorporating fullerenes, have gained additional interest due to their properties suitable for energy storage applications, e. g. for batteries 10-13 and hydrogen storage. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Correlation between structural properties of Na-and Li-based fullerides and their chemical and physical characteristics have been studied extensively by many techniques, including powder X-ray and neutron diffraction (PXD and PND, respectively), 15,17,[19][20][21][22][23][24][25][26][30][31][32][33] nuclear magnetic resonance (NMR), 26, 28, 34 differential scanning calorimetry (DSC), 20,22,26,29 infrared spectroscopy (IR). 17,19,[25][26] However, the published results still lead to contradictory conclusions about sample phase compositions and metal(M):C60 ratios.…”