Electrocatalytic Activity of Oxide and Carbon Nanotube Supported Platinum Particles in Fuel Cells

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Electrocatalytic Activity of Oxide and Carbon
Nanotube Supported Platinum Particles in Fuel
Cells

• Brian Seger
• Advisor Dr. Kamat
• Date8/11/06

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Outline

• Support requirements
• Improve electrocatalytic activity
• Use of SiO2 as a support
• Future research

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Fuel Cell Losses and Support Effects

• Supports can help reduce activation
  overpotentials and ohmic losses.
• Ohmic Electrode
• Proton Resistivity
• Electrical Resistivity
• Cathode Activation
• Catalyst size
• Dispersion

Model of overpotentials in a PEM fuel cell
(Bernardi 1992).
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Support Issues

• Support Surface Area
• The support should have a high surface area on
  which to disperse platinum particles.
• Enhance Electrochemically Active Surface Area
  (ECSA)
• ECSA is a measure of active surface of Pt.
• Support Inertness
• The support should not promote any side reactions
  or undergo degradation over time.

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Design of an Improved Catalyst

• For decades carbon black has been the standard
  support.
• Issues with carbon black
• Side reactions give H2O2
• Low surface area compared to nano-materials
• Corrodes
• Improvements via Silica
• High surface area by platinum salt deposition
• Inert
• Durable

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Pt-SiO2 Synthesis
PtCl62-
NaBH4 Dropwise
4 nm SiO2
H
Pt Salt SiO2
Pt-SiO2 Network
Varying amounts of NaBH4, from no NaBH4 to
excess NaBH4
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Pt-SiO2 Particles
TEM image of 2-1 Pt-SiO2 by mass catalyst
particles
FESEM image of 2-1 Pt-SiO2 deposited on carbon
Toray paper
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Platinum Lattice Fringes
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Electrochemical Analysis

• Hydrogen desorption in the cyclic voltammogram
  was used to determine ECSA.

Hydrogen Desorption
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Fuel Cell Results

• Fuel cells were made and tested keeping all
  variables constant except for the cathode. 0.2
  mg/cm2 of each specific support/catalyst was put
  onto the cathode.
• A current interrupt test was done to determine
  the ohmic resistance of the cell.

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Future Research

• Different oxides such as tungsten oxide, tin
  oxide and titanium dioxide are being investigated
  as supports.
• Use of Pt-Ru catalyst instead of a Pt catalyst on
  a silica support.
• Ways to reduce platinum on nanotubes.

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Thank You

• I would like to thank
• My advisor Dr. Kamat
• Dr. Vinodgopal and Dr. Kongkanand
• Dr. Kosel
• Alice Geglio
• Any Questions?

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Surface Area
O2 Evolution
Hydrogen Adsorption
H2 Evolution
Hydrogen Desorption
Capacitive Current, QCV or iCV/sec
Oxide Desoprtion
Oxide Adsorption
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Mass Transfer Losses
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TEM Images
0.5-1 Pt-SiO2 TEM
10-1 Pt-SiO2 TEM
2-1 Pt-SiO2 TEM
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SEM Images
FESEM image of Pt deposited on carbon Toray paper
FESEM image of 2-1 Pt-SiO2 deposited on carbon
Toray paper
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Pt-Mass normalized Fuel Cell Data
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Fuel Cell Demostration
Electric current
Diffusion Layer
Catalyst
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Hydrogen Peroxide Side Reactions
H2O2
OH Radicals
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Carbon Degradation Reaction
Water
CO2
4e- 4H
v
Carbon Black
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SEM Beam induced Agglomeration
SEM Image 0s focusing
SEM Image 90s focusing