Transcript Metal Nanoparticle/Carbon Nanotube Catalysts

Metal Nanoparticle/Carbon
Nanotube Catalysts
Brian Morrow
School of Chemical, Biological and Materials Engineering
University of Oklahoma
Introduction
Armchair
Zigzag
Chiral
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 bundles
which reduces their surface areas.
Metal nanoparticle/carbon nanotube materials
are being investigated for use in catalytic and
electrocatalytic applications such as fuel cells.
Baughman et al., Science 297 (2002) 787
A. Kongkanand, K. Vinodgopal, S. Kuwabata, P. V. Kamat, J, Phys.
Chem. B 110 (2006) 16185-16188
Example
Anode (methanol oxidation):
CH3OH + H2O → CO2 + 6H+ + 6eCathode (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!
Example
Methanol oxidation - anode
of direct methanol fuel cells
A. Kongkanand et al., J. Phys. Chem. B 110 (2006)
16185-16188
Oxygen reduction - cathode
of direct methanol fuel cells
Langmuir 22 (2006) 2392-2396
Other Examples
Selective hydrogenation
Oxidation of formic acid and
formaldehyde
Hydrogen peroxide oxidation
Environmental catalysis
Synthesis of 1,2-diphenylethane
Wildgoose et al., Small 2 (2006) 182-193
Synthesis
Metal particles can be grown directly on the carbon nanotubes
- 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
Synthesis
Already-grown metal particles can be connect to the carbon nanotubes
Hydrophobic interactions and hydrogen bonds
Covalent Linkage
Han et al. Langmuir 20 (2004) 6019
π-stacking
Coleman et al., J. Am. Chem. Soc. 125 (2003) 8722
Ou and Huang, J. Phys. Chem. B 110 (2006) 2031
Characterization
TEM/SEM
XRD
Bittencourt et al., Surf. Sci. 601 (2007) 2800-2804
AFM
D.-J. Guo and H.-L. Li, Journal of Power Sources 160 (2006) 44-49
Hrapovic et al., Analytical Chemistry 78 (2006) 1177-1183
Characterization
XPS
Raman spectroscopy
Lee et al., Chem. Phys. Lett. 440 (2007) 249-252
Lee et al., Langmuir 22 (2006) 1817-1821
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
Questions?
Characterization
“X-ray photoelectron
spectroscopy
was employed to investigate the
binding energy of d-band
electrons of Pt. As shown in
Figure 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 electronic
properties of Pt.”
A. Kongkanand et al., J. Phys. Chem. B 110 (2006) 16185-16188