Transcript No Slide Title

Roles of Carbon Nanostructures
for Advanced Energy Solutions
Prashant V. Kamat
University 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, zeroemission 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
FuelCells
Cells
2 H2
CH3OH
Anode
4 H+ + 4 eCO + 4 H+ + 4 e-
Electrical circuit
O2 (g)
Cathode
+ 4 H+ + 4 e-
2 H2O
O2 from air
Fuel H2
Used fuel recirculates
Air + water vapour
Gas diffusion electrode (anode)
Catalyst
Gas diffusion electrode (cathode)
Catalyst
Proton Exchange Membrane
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
P. V. Kamat et. al. J. Am. Chem. Soc. 126 (2004), 10757.
CNT film
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 side
Anode
C-paper
TiO2 on
C-paper
Pt/Ru on
C-paper
Pt/Ru
TiO2
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
2) Mesoporous SiO2 + sucrose + H2SO4
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.
Mesoporous SiO2
C/SiO2
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
Pt
•Disperse with nanotubes in sonicator,
microwave heating to fuse nanoparticles to
nanotubes
Cushing et al. Chem. Rev. 104 (2004), 3893.
Ni
Monolayer Pt Surface on SWNT’s
•Funtionalize SWNT’s deposited on electrode:
25-400°C, F2
•Add bis-(ethylenediamine)platinum (II) chloride:
Nucleophilic substitution
Cl-Pt-Cl
NH2
NH
NH2
NH
[(H2NCH2CH2NH2)Pt]Cl2
NH
NH
NH2
D. Tasis et. al. Chem. Rev. 106 (2006), 1105.
NH2
Cl-Pt-Cl
Monolayer Pt Surface on SWNT’s
•Reduce Pt2+ to Pt, deposit on surface
Cl-Pt-Cl
NH2
NH
NH2
NH
Pt Pt Pt
H2, 400°C
NH
NH
H2PtCl6 electrodeposition
Pt
NH2
NH2
Cl-Pt-Cl
Pt
Pt
Pt
Pt
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 Northwest
D. Meisel, Notre Dame Radiation Laboratory
Students/Postdocs
S. Barazouk, K. Drew, G. Girishkumar, I. Robel