Roles of Carbon Nanostructures for Advanced Energy Solutions

Prashant V. KamatUniversity of Notre Dame Radiation Research Laboratory

South Bend, IN

Presented by: Brian Ellis, UW

Outline

•Fuel cells, carbon nanotubes and current research

•Proposed areas of research

•Resources

Scope of Research•Fuel cells: energy conversion device

•Applications: portable electronics, home power generators, zero-emission vehicles

•Utilize carbon nanostructures (fullerenes, carbon nanotubes etc) as support to boost the electrode performance

•Design of new metal catalysts and composites for improving the efficiency of electrode reactions

•Develop membrane assembly and evaluate the overall performance in portable fuel cells (Direct methanol and hydrogen fuel cells)

GM Hy-wire GM HydroGen3

Fuel CellsFuel Cells

Electrical circuit

CatalystCatalyst

Fuel H2

Used fuel recirculates

O2 from air

Proton Exchange Membrane

Gas diffusion electrode (anode) Gas diffusion electrode (cathode)

Air + water vapour

Anode2 H2 4 H+ + 4 e-

CH3OH CO + 4 H+ + 4 e-

CathodeO2 (g) + 4 H+ + 4 e- 2 H2O

Both reactions require catalyst (Pt or Pt alloy)

Properties of SWNT’s

•Conductivity: metallic when fully aromatic•Strength: resistant to bending, stretching•Surface area: 10-20 m2/g•Porosity: hollow•Functionalization: can perform many reactions with nanotube surface to add reactive groups, pendant molecules, polymers

P. M. Tajayan. Chem. Rev. 99 (1999), 1787.D. Tasis et. al. Chem. Rev. 106 (2006), 1105.

Nanotube Applications for Fuel Cells

•Carbon nanostructures: high surface area, mechanical strength, conductivity

•Candidate materials for hydrogen storage

•Electrode surfaces: minimize use of precious metals•Maximize electrode area (porous supports for catalysts)

Recent Research in the Kamat Group

Deposition of SWNT films•One-step solubilization of SWNT: sonicate SWNT with tetraoctylammonium bromide, prevents aggregation

•Film deposition: •conducting glass plate (doped tin oxide) dipped in organo-silane to functionalize surface•Electrodeposition (50V DC)

CNT in THF CNT in THF/TOAB CNT film

P. V. Kamat et. al. J. Am. Chem. Soc. 126 (2004), 10757.

Alignment of Nanotubes in a DC Field

•Apply high DC voltage (>100V): polarization of nanotubes

•Linear bundles form, aligned perpendicular to electrode surface

+ -

+-

+ +

+ +

+

P. V. Kamat et. al. J. Am. Chem. Soc. 126 (2004), 10757.

Pt Deposition on SWNT films•CNT film immersed in solution of H4PtCl6

•Electrochemical pulses (12ms) at -350mV vs. SCE until 0.1 C reached

•Loading: 56μg/cm2 of Pt

•Pt nanoparticles: uniform size, 20nm diameter

P. V. Kamat et. al. J. Phys. Chem. B. 108 (2004), 19960.

Pt on Fullerenes

•C60 suspension in acetonitrile

•Conducting glass electrodes, electrodeposition (100V DC) produces brownish film

•Loading of Pt: fullerene film immersed in solution of H4PtCl6, electrodeposition at -350mV vs. SCE

•Pt: 100-150nm clusters

P. V. Kamat et. al., Nano Lett., 4 (2004), 415.

TiO2-Pt/Ru Hybrid Electrodes•Large band gap semiconductors (TiO2) photocatalyze methanol oxidation; supplement Pt/Ru catalyst system

• Prepared Pt-Ru catalyst brushed onto one side of carbon fiber paper; TiO2 suspension dropped onto other sideAnode

Pt/Ru TiO2

C-paper

TiO2 on C-paper

Pt/Ru on C-paper

P. V. Kamat et al. J. Phys. Chem. B. 109 (2005), 11851.

Proposed Topics of Research

Mesoporous Carbon•Deposition of carbon onto mesoporous silica

1) Sodium silicate + CTAB + non-ionic surfactant Mesoporous SiO2

2) Mesoporous SiO2 + sucrose + H2SO4 C/SiO2

3) C/SiO2 + NaOH Mesoporous C

•High Surface area (1000-2000 m2/g)

•Electrodeposit Pt nanoparticles onto C

B. Fang et. al. J. Pyhs. Chem. B. 110 (2006), 4875.

Metal Core-Pt shell Nanoparticles•Any inexpensive metal/metal oxide could be used as core (Ni, Co, Fe, Fe3O4, etc)

•Ni core:

NiCl2 + CTAB + N2H4•H2O Ni nanoparticles

•Ni core/Pt shell nanoparticles:

Ni nanoparticles + H2PtCl6 + potassium bitartarate

•Disperse with nanotubes in sonicator,microwave heating to fuse nanoparticles to nanotubes

Pt

Ni

Cushing et al. Chem. Rev. 104 (2004), 3893.

•Funtionalize SWNT’s deposited on electrode:

•Add bis-(ethylenediamine)platinum (II) chloride: Nucleophilic substitution

Monolayer Pt Surface on SWNT’s

25-400°C, F2

[(H2NCH2CH2NH2)Pt]Cl

2

NH

NH2

NH

NH2

NH2

NH

NH2

NH

Cl-Pt-Cl

Cl-Pt-Cl

D. Tasis et. al. Chem. Rev. 106 (2006), 1105.

Monolayer Pt Surface on SWNT’s

H2PtCl6

electrodepositionNH

NH2

NH

NH2

NH2

NH

NH2

NH

Cl-Pt-Cl

Cl-Pt-Cl

H2, 400°C

PtPt PtPt

PtPt

Pt

Pt

•Reduce Pt2+ to Pt, deposit on surface

Aligned SWNTs

•Increase the concentration of nanotubes to cover electrode

Aligned SWNTs: Hydrogen Storage

•Dissolve electrode in acid, network of aligned SWNT’s remains

•Potential material for hydrogen storage

H2

Exact mechanism and sites for absorption not known

Purchases•Brunauer, Emmett, Teller (BET) surface area equipment ($50,000)

•Raman spectrometer for characterizing CNT’s ($180,000)

Conclusions

•Carbon nanostructures have physical properties (high conductivity, strength, porosity) applicable for use in fuel cells

•Utilize these materials for increasing the surface area of electrodes and hydrogen storage

•Deposit Pt nanoparticles or mixed core-shell nanoparticles to minimize the amount of precious metals consumed

Acknowledgements

Collaborators

K. Vinodgopal, Indiana University NorthwestD. Meisel, Notre Dame Radiation Laboratory

Students/Postdocs

S. Barazouk, K. Drew, G. Girishkumar, I. Robel