Metal Nanoparticles for the Production of Carbon Nanotube Composite

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Materials Science and Engineering C 19 Ž2002. 119–123
www.elsevier.comrlocatermsec

Metal nanoparticles for the production of carbon nanotube composite materials by decomposition of different carbon sources
A. Weidenkaff a, ) , S.G. Ebbinghaus a , Ph. Mauron b, A. Reller a , Y. Zhang a , A. Zuttel b ¨
a

Institute of Solid State Chemistry, UniÕersitat Augsburg, UniÕersitatsstr. 1, D-86159 Augsburg, Germany ¨
¨
b
Physics Department, UniÕersite de Fribourg, Perolles, CH-1700 Fribourg, Switzerland ´
´

Abstract
Carbon nanotube composite materials were produced by catalytic decomposition of gaseous carbon sources Žsuch as carbon monoxide or hydrocarbons. on nanometer-size metal clusters of iron, cobalt and nickel embedded in matrices of inert metal oxide particles. The resulting multiwalled carbon nanotubes are several micrometers long with tube diameters ranging from 5 to 20 nm. A fluidised bed reactor was developed for a large-scale synthesis of the carbon nanotubermetal oxide composite ŽCMC. material. Hydrogen storage capacities of these materials were tested by volumetric and electrochemical methods. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Carbon nanotubes; Functional materials; Hydrogen storage; Electron microscopy

1. Introduction
Carbon nanotubes have interesting physical properties
such as high mechanical stability, large surface area, novel electronic properties Ž1D band structure., and very good
thermal and chemical stability w1–3x. There are many
publications on the production of nanotubes, but commercially available material is still expensive and often of poor quality. The reason is a difficult purification process to
separate the carbonaceous material from the metallic or
ceramic catalyst. The hydrogen storage capability of pure
carbon nanotubes is in contrast to what has been published
before Ž- 2 wt.%.. In combination with transition metals,
hydrogen storage capacities of more than 6 wt.% can be
reached as shown unintentionally by Dillon et al. w4x by
using an ultrasonic treatment for CNT purification. However, recently, Hirscher and et al. w5x have shown that the hydrogen was absorbed in the TiV alloy and not in the
nanotubes as claimed by Dillon et al.
An intended combination of carbon nanotubes and metal
hydrides as new storage materials—with nanotubes grown
directly on, for example, LaNi 5 —could lead to very high
hydrogen storage capacities. With the combination of the
properties of the metal-containing part and the carbon

)

Corresponding author. Tel.: q
49-821-598-3270; fax: q
49-821-5983002.
E-mail address: anke.weidenkaff@physik.uni-augsburg.de
ŽA. Weidenkaff..

nanotubes in a carbon nanotubermetal oxide composite
ŽCMC., the purification process can be avoided. An example for nanotubermetal oxide composite materials are carbon nanotubes grown on the surface of insulating ceramics. The resulting novel materials have a high electrical conductivity w6x.

In this paper, we describe the synthesis of different
carbon nanotubermetal oxide composites. Since the structure of the carbon nanotubes determines upon their physical properties, the influence of the catalytically active particles’ shape and size as well as the nature of catalyst on the structure of the carbon nanotubes was studied by

high-resolution transmission electron microscopy. The most
promising results were obtained with catalysts that are
prepared in situ in a matrix of inert metal oxide to prevent agglomeration effects.

2. Experimental
The synthesis of the carbon nanotube composite materials proceeds in four steps: 1. Preparation of the catalyst precursors: Ža. as nanometal oxide particles, Žb. as solid solution in inert metal oxides, or Žc. by coating of inert support

material.
2. Precursor decomposition by combustion or calcination and formation of the metal oxide. 3. Formation of active sites Žs nanometer-sized cluster

0928-4931r02r$ - see front matter q 2002...
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