L Journal of Alloys and Compounds 330–332 (2002) 654–658 www.elsevier.com / locate / jallcom Hydrogen storage in carbon nanostructures a, a a b b b * M. Hirscher , M. Becher , M. Haluska , A. Quintel ,V. Skakalova , Y.-M. Choi , b b c c d d U. Dettlaff-Weglikowska , S. Roth , I. Stepanek , P. Bernier , A. Leonhardt , J. Fink a ¨ Max-Planck-Institut f ur Metallforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany b ¨ ¨ Max-Planck-Institut f ur Festkorperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany c Groupe de Dynamique des Phases Condensees, University of Montpellier II, F-34095 Montpellier Cedex 5, France d ¨ ¨ Institut f ur Festkorper- und Werkstofforschung, D-01177 Dresden, Germany Abstract The paper gives a critical review of the literature on hydrogen storage in carbon nanostructures. Furthermore, the hydrogen storage of graphite, graphite nanofibers (GNFs), and single-walled carbon nanotubes (SWNTs) was measured by thermal desorption spectroscopy (TDS). The samples were ball milled under Ar or D atmosphere in order to modify the microstructure which was characterized by X-ray 2 diffraction, scanning electron microscopy, and transmission electron microscopy. These investigations show a reversible hydrogen storage only for SWNTs and in addition indicate that an opening of the SWNTs is essential to reach high storage capacities.  2002 Elsevier Science B.V. All rights reserved. Keywords: Hydrogen storage; Graphite nanofibers; Carbon nanotubes 1. Introduction In the 70s graphite nanofibers (GNFs) were discovered which consist of graphite platelets stacked together in The time span for commercializing fuel cell vehicles various orientations to the fiber axis with an interlayer may be drastically shortened if an adequate hydrogen spacing similar to bulk graphite. The length of these GNFs storage device will be found in the near future. The first can vary between 5 and 100 mm and their diameter report [1] on hydrogen storage in single-walled carbon between 5 and 200 nm. For details on the structure see nanotubes (SWNTs) estimated a high possible storage Refs. [2,3]. In the present paper we only mention one capacity for purified material and initiated a tremendous configuration of GNFs the so-called herringbone type research activity on SWNTs as well as graphite nanofibers where graphite sheets are stacked with a certain angle to (GNFs) concerning their hydrogen uptake. In the present the fiber axis or conically shaped graphite sheets are paper we will give a critical review of the literature. stacked. In transmission electron microscopy investigations Furthermore, own measurements of the hydrogen storage both structures yield in projection a fish-bone like image. on SWNTs and GNFs will be shown. Concerning a possible hydrogen uptake, geometrically, this structure possesses advantages due to the accessibility of all sheets from the outside and short diffusion paths into 2. Carbon nanostructures the nanostructure. The discovery of the fullerenes opened the door to a The three well-known forms of carbon are diamond, new class of carbon materials. Carbon nanotubes were first graphite and fullerenes. In diamond each carbon has four observed in 1991 by Iijima [4]. Simply speaking these bonds to its neighbors and forms a three-dimensional nanotubes are built of a finite graphite sheet which is rolled lattice. Graphite is built up of two-dimensional hexagonal to a tube. A variety of types exists which is either made of sheets of carbon atoms where the carbon carbon distance one layer and therefore called single-walled nanotube ˚ in plain is 1.42 A and the distance between the sheets is (SWNT) or more than one layer called multi-walled ˚ 3.35 A. nanotube (MWNT) (for details see Ref. [5]). Here we focus on SWNTs which can be prepared with diameters between 1 and 2 nm. Typically, these SWNTs have caps at *Corresponding author. E-mail address: hirscher@mf.mpg.de (M. Hirscher). the end which have structures related to the fullerenes. 0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01643-7