Hydrogen Storage in Mesoporous Titanium Oxide-Alkali Fulleride

Mesoporous titanium oxide-alkali fulleride composites were synthesized and characterized by X-ray diffraction, nitrogen adsorption, Raman spectroscopy, and elemental analysis. The hydrogen sorption properties of these composites were investigated at 77 K, room temperature, and 200 degrees C. A maximum overall volumetric uptake of 27.35 kg/m(3) was obtained for the lithium fulleride composite at 77 K and 100 atm, compared with 25.48 kg/m(3) for the pristine unreduced material under the same conditions. This value was less than those previously reported for bis(toluene)titanium- and bis(benzene)vanadium-reduced materials (40.46 and 33.42 kg/m(3), respectively) and also less than those found for the fulleride-free Li- and Na-reduced materials in this study (28.10 and 28.19 kg/m(3), respectively). At room temperature and 100 atm, the maximum gravimetric storage and adsorption values of fulleride-impregnated composites were 0.99 and 0.11 wt %, respectively, while the corresponding amounts for unreduced material were 0.94 and 0.10 wt %. At 200 degrees C and 100 atm, the maximum gravimetric storage and adsorption capacities of fulleride composites were less than those of the unreduced material, which were 0.62 and 0.06 wt %, respectively. Thus, inclusion of fulleride units in the pores lowered the overall gravimetric and volumetric storage relative to the fulleride-free Na- and Li-reduced counterparts. Like other reduced composites studied in our group, the enthalpies of the reduced composites showed an unusual increasing trend with surface coverage, with the greatest value (6.55 kJ/mol) measured for the Na-reduced fulleride composite. This suggests that the reduced titanium oxide surface provides the majority of the binding sites in these materials.