Title: Nafion
1 Nafion Membrane Treatment
For Direct Methanol Fuel
Cell (DMFC) Applications
- Presented by Darius Agoumba
- Advised by Dr. Thrasher
2Generalities 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.
3Shortcuts 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.
4 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.
5 Methanol Permeability Through Doped
Nafion Membrane
The size only of counter ions doesnt decrease
the methanol flow.
6 Ratio of Proton conductivity to MeOH
Permeability
Proton conductivity of the
membrane increases when
the membrane is dipped back in acid.
7 Pretreatment Influence on the Methanol
Permeability Through Nafion? Membranes
Membrane treatment is important in the evaluation
of the methanol permeability in DMFCs
8 Reduction of Methanol Crossover in the
DMFC
NF-117 used as-received and doped reduces the
methanol crossover in DMFCs.
9 XPS of the Nafion? Membrane As-Received (NAR)
No evidence of any other ions on the surface of
the Nafion membrane used as-received
10XPS of the Nafion? Membrane Pretreated (NAP)
No evidence of any other ions on the surface of
the pretreated Nafion membrane
11EDAX of the Nafion?Membrane As-Received (NAR)
12EDAX of the Nafion? Membrane Pretreated (NAP)
Reduction of the trace of the metallic ion seen
in the NAR
13EDAX Results Conclusions
Evidence of Potassium ion in the membrane
14ICP Elemental Analysis Results
ICP Results
Evidence of other metallic ions in the membrane
15Partial 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.
16 Principles of the DMFC
17 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
18 How work the DMFC
N2 is used at the cathode side to evaluate
the MeOH
crossover.
19Electro-Oxidation of Methanol and Water
Through NAR
20 Electro-Oxidation of Doped Nafion? 117
Membranes
21Nafion? 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
22Obtained 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
23 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.
24 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.
25 Aknowlegments
- The University of Alabama
- The Chemistry department
- The CAVT research group
- Dr. Thrasher
- My dissertation committee members
- Dr. Waterfield
- Dr. Fernandes
- Dr. Obrian
26U of A Chemistry Department