Nafion

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Nafion Membrane Treatment
For Direct Methanol Fuel
Cell (DMFC) Applications

• Presented by Darius Agoumba
• Advised by Dr. Thrasher

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Generalities on the DMFC

• DMFC is an electrochemical engine which is able
  to convert the free energy change of a chemical
  reaction directly into electrical energy.
• DMFC is capable to work at much lower
  temperatures and with reduced polluting emissions
  (60C-130 C) .
• DMFC doesnt require any fuel processing
  equipment.

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Shortcuts of the DMFC

• Crossover of methanol through the Nafion?
  membrane.
• CO contamination on the DMFC anode.
• Formation of CHOH and HCOOH if adequate catalyst
  is not used.

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Research objectives

• Evaluation of the different pretreatments methods
  on the permeability of Nafion membrane to
  methanol solution.
• Reduction of the methanol crossover in the DMFC.

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Methanol Permeability Through Doped
Nafion Membrane
The size only of counter ions doesnt decrease
the methanol flow.
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Ratio of Proton conductivity to MeOH
Permeability
Proton conductivity of the
membrane increases when
the membrane is dipped back in acid.
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Pretreatment Influence on the Methanol
Permeability Through Nafion? Membranes
Membrane treatment is important in the evaluation
of the methanol permeability in DMFCs
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Reduction of Methanol Crossover in the
DMFC
NF-117 used as-received and doped reduces the
methanol crossover in DMFCs.
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XPS of the Nafion? Membrane As-Received (NAR)
No evidence of any other ions on the surface of
the Nafion membrane used as-received
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XPS of the Nafion? Membrane Pretreated (NAP)
No evidence of any other ions on the surface of
the pretreated Nafion membrane
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EDAX of the Nafion?Membrane As-Received (NAR)
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EDAX of the Nafion? Membrane Pretreated (NAP)
Reduction of the trace of the metallic ion seen
in the NAR
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EDAX Results Conclusions
 
 
Evidence of Potassium ion in the membrane
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ICP Elemental Analysis Results
ICP Results  
Evidence of other metallic ions in the membrane
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Partial Conclusions

• Pretreatment of Nafion membrane is very
  important.
• Nafion membrane as pretreated by other research
  group is not in a true acidic form but in a
  potassium ion form.
• Metallic ions probably favor the intrusion of the
  Cesium ion in the membrane during the doping
  process.

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Principles of the DMFC

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Electrochemical Reactions in the DMFC

• Anode CH3OH H2O CO2 6H 6e-
• Cathode 3/2 O2 6H 6e- 3H2O
• Overall CH3OH 3/2 O2 CO2 2H2O
• E -?Gf /ZF,
• For methanol ?Gf - 698.2 KJ.mol-1
• E 1.21 Volts

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How work the DMFC
N2 is used at the cathode side to evaluate
the MeOH
crossover.
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Electro-Oxidation of Methanol and Water
Through NAR
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Electro-Oxidation of Doped Nafion? 117
Membranes
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Nafion? 117 Conductance
s l / RS   l thickness of the
electrolyte film R resistance of the
electrolyte film S cross-section of the
electrolyte film
With l S, s 1/R Practical Conductivity or
Conductance (C ) 1/R in ?-1Cm-1  
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Obtained Conductance for Nafion? 117
From the previous electro-oxidation
data RNAP/MeOH 1.8441 ? RNAP/H2O 3.6918
? RNAPCs/MeOH 0.0711? RNAP(CH3)4N/MeOH
0.0190 ?     C NAP/MeOH 9.9235x10-6?-1Cm-1 C
NAP/H2O 4.9569x10-6?-1Cm-1 C NAPCs/MeOH
2.5738x10-4?-1Cm-1 C NAP(CH3)4N/MeOH
9.6315x10-4?-1Cm-1
Conductance increases with decreasing MeOH
concentration
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Conclusions

• CsF and (CH3)4NCl are good doping materials for
  Nafion 117 membrane.
• Doped membrane need appropriate parameters to
  operate efficiently.
• Nafion 117 membrane as pretreated is not
• in acid form but in a potassium ion form.

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Future Goals

• Dope the Nafion membrane with Ionic liquids and
  check the methanol permeability along with the
  conductivity of the membrane.
• Search for other fuels with increase current
  density and lower fuel permeability with Nafion
  membrane.

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Aknowlegments

• The University of Alabama
• The Chemistry department
• The CAVT research group
• Dr. Thrasher
• My dissertation committee members
• Dr. Waterfield
• Dr. Fernandes
• Dr. Obrian

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U of A Chemistry Department