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Metal Nanoparticle/Carbon Nanotube Catalysts. Brian Morrow School of Chemical, Biological and Materials Engineering University of Oklahoma. A. Kongkanand, K. Vinodgopal, S. Kuwabata, P. V. Kamat, J, Phys. Chem. B 110 (2006) 16185-16188. Introduction. Armchair. Zigzag. Chiral.

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metal nanoparticle carbon nanotube catalysts

Metal Nanoparticle/Carbon Nanotube Catalysts

Brian Morrow

School of Chemical, Biological and Materials Engineering

University of Oklahoma

introduction

A. Kongkanand, K. Vinodgopal, S. Kuwabata, P. V. Kamat, J, Phys. Chem. B 110 (2006) 16185-16188

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

example
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!

example4

A. Kongkanand et al.,J. Phys. Chem. B 110 (2006) 16185-16188

Example

Methanol oxidation - anode of direct methanol fuel cells

Oxygen reduction - cathode of direct methanol fuel cells

Langmuir 22 (2006) 2392-2396

other examples

Wildgoose et al., Small 2 (2006) 182-193

Other Examples

Selective hydrogenation

Oxidation of formic acid and formaldehyde

Hydrogen peroxide oxidation

Environmental catalysis

Synthesis of 1,2-diphenylethane

synthesis
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

synthesis7
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

XRD

D.-J. Guo and H.-L. Li, Journal of Power Sources 160 (2006) 44-49

Characterization

TEM/SEM

Bittencourt et al., Surf. Sci. 601 (2007) 2800-2804

AFM

Hrapovic et al., Analytical Chemistry 78 (2006) 1177-1183

characterization9

XPS

Lee et al., Langmuir 22 (2006) 1817-1821

Characterization

Raman spectroscopy

Lee et al., Chem. Phys. Lett. 440 (2007) 249-252

future directions
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
characterization13
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