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Metal Nanoparticle/Carbon
Nanotube Catalysts
Brian Morrow
School of Chemical, Biological and Materials Engineering
University of Oklahoma
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Introduction
A. Kongkanand, K. Vinodgopal, S. Kuwabata, P. V. Kamat, J , Phys.Chem. B 110 (2006) 16185-16188
Carbon nanotubes have many properties
which make them ideal supports for catalytic
metal nanoparticles.
However, the surfaces of nanotubes are
relatively inert, and they tend to form bundleswhich reduces their surface areas.
Metal nanoparticle/carbon nanotube materials
are being investigated for use in catalytic and
electrocatalytic applications such as fuel cells.
Armchair Zigzag Chiral
Baughman et al., Science 297 (2002) 787
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Example
Anode (methanol oxidation):
CH3OH + H2O CO2 + 6H+ + 6e-
Cathode (oxygen reduction):(3/2)O2 + 6H+ + 6e- 3H2O
Overall:
CH3OH + (3/2)O2 CO2 + 2H2O
K. Kleiner, Nature 441 (2006) 1046-1047
Possibility for powering devices such as cell phones and computers:- Potentially 3-10 times as much power as a battery
- Methanol cheaper and easier to store than hydrogen
Problems:
- Methanol crossover
- Requires catalysts, usually platinum expensive!
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Example
Methanol oxidation - anode
of direct methanol fuel cells
A. Kongkanand et al., J. Phys. Chem. B 110 (2006)16185-16188
Langmuir 22 (2006) 2392-2396
Oxygen reduction - cathode
of direct methanol fuel cells
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Wildgoose et al., Small 2 (2006) 182-193
Other Examples
Selective hydrogenation
Oxidation of formic acid andformaldehyde
Hydrogen peroxide oxidation
Environmental catalysis
Synthesis of 1,2-diphenylethane
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Synthesis
- Precursor metal salts (H2PtCl6,
H2PdCl6, etc.) heated and reduced
- Particle size can be controlled by
temperature and reducing
conditions
- Particles can be anchored by
oxidizing nanotubes (via acid
treatment or microwave irradiation),but this can also damage the
nanotubes
Georgakilas et al., J. Mater. Chem. 17 (2007) 2679-2694
Other techniques include chemical vapor deposition, electrodeposition, laser ablation,
thermal decomposition, substrate enhanced electroless deposition
Metal particles can be grown directly on the carbon nanotubes
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SynthesisAlready-grown metal particles can be connect to the carbon nanotubes
Covalent Linkage
Coleman et al., J. Am. Chem. Soc. 125 (2003) 8722
Hydrophobic interactions and hydrogen bonds
-stacking
Han et al. Langmuir 20 (2004) 6019
Ou and Huang, J. Phys. Chem. B 110 (2006) 2031
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CharacterizationTEM/SEM
Bittencourt et al., Surf. Sci. 601 (2007) 2800-2804
AFM
Hrapovic et al., Analytical Chemistry 78 (2006) 1177-1183
D.-J. Guo and H.-L. Li, Journal of Power Sources 160 (2006) 44-49
XRD
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Characterization
XPS
Lee et al., Langmuir 22 (2006) 1817-1821
Raman spectroscopy
Lee et al., Chem. Phys. Lett. 440 (2007) 249-252
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Future Directions
- Minimizing use of expensive metals
- Synthesis techniques that yield nearly monodisperse
nanoparticle size distributions
- Synthesis techniques that can control final structure of
nanoparticles
- Better understanding of metal-carbon nanotube interactions
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Questions?
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Characterization
A. Kongkanand et al., J. Phys. Chem. B 110 (2006) 16185-16188
X-ray photoelectron
spectroscopy
was employed to investigate the
binding energy of d-band
electrons of Pt. As shown inFigure 6, a shift of 0.4 eV to a
higher binding energy was found
in both 4d and 4f electrons of Pt
deposited on PW-SWCNT,
proving the role of SWCNTs in
modifying the electronicproperties of Pt.