Direct Methanol Fuel Cell

1
Direct Methanol Fuel Cell

• Operation
• liquid feed, no pressure
• fuel 3 MeOH in H2O
• Reactions
• Anode CH3OH H2O ? CO2 6H 6e-
• Cathode 1.5O2 6H 6e- ? 3H2O
• --------------------------------------------------
  ------
• Cell CH3OH 1.5O2 ? CO2 2H2O
• Challenges
• MeOH permeation thru electrolyte
• catalyst performance Pt-Ru 8 mg/cm2

JPL demo
2
Fuel Cell Challenges

• Direct H2/O2
• Hydrogen infrastructure and on-board storage
• Complex system
• Public acceptance
• Reformed H2/O2
• Very complex system
• Costly, heavy, components fail
• Target cost 2000 engine ? 40/kW today
  2-300/kW
• Direct Methanol Fuel Cell
• Fuel crossover ? low efficiency
• Poor catalyst performance

3
Approaches

• H2 storage materials
• Improved reformers
• high H2 yield catalysts
• fewer components
• Improved FC catalysts
• less costly than Pt
• higher CO tolerance
• direct hydrocarbon use

• Alternative membranes
• no humidification ? system simplification
• elevated T operation ? increased CO tolerance
• impermeable to fluids (H2, O2, CH3OH)
• Economic incentives to users manufacturers

4
Improved Catalysts
Tom Zawodzinsky, LANL
5
Alternative Membranes

• Ideal Membrane
• insensitive to humidity
• stable to 200C
• impermeable to gases
• impermeable to MeOH
• high conductivity
• good mechanical properties at 100mm

• Candidates Solid Acids
• inorganic
• impermeable
• decomp/melt 150-250C
• water soluble
• operate at T gt 100C
• poor mechanical props
• polymer composites

6
Solid Acids

• Chemical intermediates between normal salts and
  normal acids acid salts
• ½(Cs2SO4) ½(H2SO4) -gt CsHSO4
• Physical properties like salts
• Structural disorder at high T

Conductivity
7
Solid Acid Fuel Cell

• Electrolyte
• 1 1.5 mm thick CsHSO4
• Electrocatalyst
• Pt C CsHSO4
• 4 50 mg Pt / cm2
• Current collector
• Graphite paper
• H2 / O2 configuration

8
Solid Acid Fuel Cell Performance
Measured
Predicted for thin membranes

• Measured voltage drop primarily from membrane
  resistance
• Predicted comparable to Nafion at 50 mm, much
  better at 25 mm

9
Composite Membranes
Conductivity
Microstructure
Potential route to ultrathin, robust membranes
10
Future Outlook

• Many technical issues to be solved
• fuel cell system weight, size, complexity, cost
• electrolyte and catalyst performance
• fuel cell longevity under harsh conditions
• Advantages offered justify continued efforts
• efficiency, zero emissions, low noise
• alternative membranes may be the key
• Hundreds of FC demonstration sites/vehicles
• Commercial viability within 5 yrs

11
Acknowledgements

• Graduate Students
• Dane Boysen, Calum Chisholm
• Staff
• Ryan Merle
• Undergraduates
• Lisa Cowan, Gregorio Drayer, Jasper Loverio
• Funding
• National Science Foundation, California Energy
  Comission, Office of Naval Research, Caltech