New high temperature polymer electrolytes and MEAs

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New high temperature polymer electrolytes and MEAs

• M.K. Daletou, M. Geormezy, Stylianos G.
  Neophytides
• and Joannis Kallitsis
• Institute of Chemical Engineering and High
  Temperature Processe
• Department of Chemistry, University of Patras
• ADVENT Technologies

Rusnanotech 6-8 October, 2009, Moscow
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• Half Reactions on the electrodes

?2
Anode
2? 2e-
1/2 O2 2H 2e-
?2?
Cathode

• Total Reaction

?2
1/2 O2
H2O
3
Typical current-voltage Plot of a fuel cell
Activation overpotential
Ohmic overpotential
Concentration overpotential
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OUTLINE

• New High temperature H3PO4 imbibed polymer
  Electrolytes
• Physicochemical Characterization
• Gas Permeability experiments
• Water absorption experiments based on TGA
  measurements
• Effect of water on conductivity and polarization
  resistance
• Proton conduction mechanism

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Why high temperature PEM fuel cells?

• Increases the reactions kinetic rate

Lower quantity of the expensive Pt catalyst on
the electrodes

• Increase of the catalysts CO tolerance
• (10-20 ppm 80ºC, 1000 ppm 130ºC, 30000 ppm
  200ºC)

Possibility to use not so pure ?2 or other fuel

• Simplifications
• (internal reformer, cooling system)
• Threefold increase of volume Power Density

• Less complexity

• Reduced cost

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Properties of the Ideal Electrolyte

• High ionic conductivity

• Electron insulator

• Good mechanical properties

• Chemical stability

• Thermal stability

• Oxidative stability

• Low gas permeability

• Low cost

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PBI/H3PO4
?3PO4
? donor site
? acceptor site

• High thermal stability (?d500 ºC)

• High Tg(440 ºC)

• High ionic conductivity

Drawbacks

• Brittle
• Low TG when imbibed with H3PO4
• Low oxidative stability (in H2O2)

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Design of new High temperature polymer membranes
Thermal and Chemical Stability Aromatic
Polyether
High Ionic Conductivity --- Ability to Dope
with Acids Introduction of sites that act
as proton acceptors
Pyridine
Aromatic polyethers with pyridine units
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Formation of various polymer chemical structures
with Tailormade properties
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ADVENT TPS Copolymer
DMF, Tol K2CO3
High temperature polycondensation
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Properties of Advent TPS
TGA before(?) and after (?) treatment with H2O2
DMA before(?) and after (?) treatment with H2O2
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RAMAN shift during impregnation with H3PO4
Imidazol protonation
PBI

TPS
Pyridine protonation
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Morphology of the undoped and doped membranes
Doped
undoped
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Water vapors permeability
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Fuel Cell operation water detected at the anode
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MS Signals at the Anode
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Thermogravimetric Analysis
Initial Membranes Doping Level with H3PO4 85,
DL 180 wt
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Effect of PH2O on the weight of the membrane
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Water solvation
H3PO4H2OH2PO4-H3O
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Hydration enthalpies
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• Electrochemical characterization
• Ionic conductivity
• Electrochemical Interface polarizability

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Electrochemical Impedance Spectroscopy
Rp
RO
Cdl
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Both electrolyte and polarization resistances
vary with water content
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s vs H2O
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Conductivity Arrhenius plots
H3PO4H2OH2PO4-H3O
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Proton transfer
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RO vs H2O
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s vs 1/Rp
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The effect of water vapours on the reactivity of
H2 on the Pt electrochemical interface
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Fuel cell operation
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Conclusions

• New aromatic polyethers bearing pyridine units
  were synthesized
• They interact strongly with the H3PO4
• They have good film forming properties even after
  doping with H3PO4
• They are characterized by very stable chemical
  structure
• Water vapors penetrate the membrane following the
  hydration reactions
• The polymer matrix plays a significant role in
  the hydration process absorbing water more
  strongly than pure phosphoric acid
• The water uptake increases the ionic density of
  the membrane and facilitates the proton
  conductivity as the proton carrier
• Water vapors were shown to increase the
  reactivity of Had on the Pt surface

H3PO4H2OH2PO4-H3O
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Acknowledgements
Financial Support
European Commission
ENERGY K5-CT-2001-00572 (2001-2004)
Advanced PEM fuel cells
INCO-PROMETHEAS ICA2-CT-2001-10037 (2002-2005)
Membrane Cell Hydrogen Generator and
Electrocatalysis for Water Splitting.
APOLLON B project NMP3-CT-2006-033228 (2006-2009)
Polymer Electrolytes and non noble Metal
Electrocatalysts for HT PEM Fuel Cells
National Programs
E??? (2003-2006), GSRT Ministry of Development
PEM Fuel Cell Electricity Generator Operating on
Methanol
PYTHAGORAS (2004-2006), Ministry of Education
Synthesis Characterization of Polymeric
Membranes for High Temperature Fuel Cell
Applications
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Effect of steam content on the electrocatalytic
activity of the cathode
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AC impedance plots at 200oC, at various steam
contents introduced at the cathode. TPS copolymer
and Pt/C electrocatalysts
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Effect of steam content on ionic resistance Ri,
polarization resistance Rp, and current density I
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Autocatalytic role of water

• HOad?OHad
• HOHad?H2O
• H2OOad ? 2OHad

A fast Reaction step 3 will result in the bypass
of the limiting Reaction step 1
S.Völkening, K. Bedürftig, K. Jacobi, J.
Wintterlin, and G. Ertl, Phys. Rev. Let.
83,13,(1999), 2672.
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Conclusions
Electrocatalytic effect of water on the
electrochemical oxidation of ?2 to ? Is
attributed to the increase of the exchange
current density due to the increase of the
concentration of the Charge cornier in the
membrane
In addition at the cathode the presence of steam
enhances the electrocatalytic rate of o reduction
contributing in the increase of OHad H2OOad ?
2OHad
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Pyridine Monomer Synthesis
1
2
b
c
d
e
e
b
a
3
NMR
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N.Gourdoupi, A.K. Andreopoulou, V. Deimede, J.K.
Kallitsis, Chem.Mater., 2003, 15, 5044
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High Temperature polycondensation
X
Y
DMF, Tol K2CO3
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Screening

• Nuclear Magnetic Resonance (NMR)

• Size Exclusion Chromatography (SEC)

• Dynamic Mechanical Analysis (DMA)

• Thermogravimetric Analysis (TGA)

• Doping with ?3??4 85

• Ionic Conductivity Measurements (4-probe)