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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.