Chem. Mater. 2007, 19, 135-137
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Hydrogen Storage Property on Nickel-Atom-Dispersed Organosilica Nanotubes Se Yun Kim,† Jung Woo Lee,† Jong Hwa Jung,‡ and Jeung Ku Kang*,† Department of Materials Science and Engineering, Korea AdVanced Institute of Science and Technology, Daejon 305-701, Republic of Korea, and Department of Chemistry and Research Institute of Natural Science, Gyeongsang National UniVersity, Chinju 660-701, Republic of Korea ReceiVed October 2, 2006 ReVised Manuscript ReceiVed December 6, 2006
Hydrogen, which can be readily produced from renewable energy sources, contains a much larger chemical energy per mass (142 MJ kg-1) than any hydrocarbon fuel. For example, a hydrogen electric fuel cell car, where hydrogen in a fuel cell is burnt electrochemically with oxygen from air, needs to store only about 4 kg of hydrogen to cover the range (∼300 miles) of a gasoline-powered car, while generating only environmentally clean water as a byproduct. Consequently, hydrogen is considered to be an ideal fuel for solving an energy crisis and helping alleviate the earth’s environmental problems that result from using petroleum fuels. The U.S. Department of Energy has targeted a maximum weight percent (wt %) of reversibly adsorbed hydrogen of 6.5% and a maximum hydrogen capacity per volume of 62 kg m-3 for many applications, including vehicles and portable devices. However, a major problem is that there is no hydrogenstorage material as yet developed that can allow the release of 6.5 wt % (target of the Department of Energy, DOE) hydrogen at practical atmospheric temperatures and pressure conditions, which are the usual conditions for cars and the ideal conditions for many other practical applications. Thus far, several hydrogen-storage methods such as carbon-fiber-reinforced high-strength containers,1 liquid hydrogen,2 chemical hydrides,3 and carbon nanotubes (CNTs)4 have been suggested. Hydrogen storage in a gas or liquid phase is a relatively unsuitable system for a vehicle because it is dangerous and expensive.5 Bearing this in mind, there is a high level of interest in storing hydrogen on lightweight metals and advanced carbons. Many metals are capable of absorbing large amounts of hydrogen in the interstitial sites of their lattices, where hydrogen molecules are dissociated to the atoms at the surface of the metal before absorption. Although metal hydride is a potential hydrogen-storage material, some problems have to be overcome before it can be put into practical use, such as the slow kinetics during hydride formation and decomposition.6 On the other hand, * Corresponding author. Tel: +82-42-869-3338. Fax: +82-42-869-3310. E-mail:
[email protected]. † Korea Advanced Institute of Science and Technology. ‡ Gyeongsang National University.
(1) Takeichi, N.; Senoh, H.; Yokota, T.; Tsuruta, H.; Hamada, K.; Takeshita, H. T.; Tanaka, H.; Kiyobayashi, T.; Takano, T.; Kuriyama, N. Int. J. Hydrogen Energy 2003, 28, 1121. (2) Aceves, S. M.; Martinez-Frias, J.; Garcia-Villazana, O. Int. J. Hydrogen Energy 2000, 25, 1075. (3) Sandrock, G.; Thomas, G. Appl. Phys. A 2001, 72, 153. (4) Wang, Q.; Johnson, J. K. J. Chem. Phys. 1999, 110, 577. (5) Schlapbach, L.; Zu¨ttel, A. Nature 2001, 414, 353.
Figure 1. (a) PW91 optimized organosilica nanotube structure with the periodic boundary condition, (b) its magnified view after physisorption, and (c) its magnified view after chemisorption of two hydrogen atoms on a benzene ring. O, Si, C, and H atoms are shown in green, gray, light brown, and pink, respectively.
carbon nanotubes (CNTs) have been proposed as being a promising candidate for hydrogen storage since the first experimental study by Dillon et al.7 A CNT has a cylindrical structure and a high surface-to-volume ratio, which makes it ideal for the development of reversible hydrogen storage. However, recent studies show that the hydrogen content on a pristine CNT is releasable only in negligible amounts (
