325 steevn

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325 steevn

  1. 1. Simon Fraser University
  2. 2. Model Polymers for Fuel Cell Membranes. E.M.W. Tsang, A. Yang, Z. Shi, T. Weissbach, R. Narimana,# B. Frisken,# S. Holdcroft* Dept. of Chemistry (Physics#) Simon Fraser University Burnaby, British Columbia Canada Dec, 2013, ICAER 2013 Funding: 2
  3. 3. Proton Exchange Membrane Fuel Cell (PEMFC) eProton Exchange Membrane (PEM) HO 2 e- Anode Reaction Cathode Reaction 2H 4H ++ 4e 2 (Hydrogen) H+ H 2 Catalyst O + 4H ++ 4e2 O 2 Electrode 2H O 2
  4. 4. Fuel Cells – Stacks Bi-polar plate Automotive: 80,000 W ~350-400 MEAs 750 Bipolar plates flow field MEA electrode backing gasket
  5. 5. Structure of Nafion (PFSI) CF2 CF2 x CF CF2 y OCF2CF z O(CF2)2SO3H CF3 1 micron (1/1000 mm)
  6. 6. Perfluorinated vs Hydrocarbon PEMs Advantages •• •• •• •• •• High proton conductivity High proton conductivity Efficient even at low operating temp Efficient even at low operating temp Good mechanical properties Good mechanical properties High durability High durability Good flexibility at low temp Good flexibility at low temp Disadvantages •• •• •• •• Very expensive Very expensive High H22,O22,, N22 & methanol crossover High H ,O N & methanol crossover Humidification necessary Humidification necessary Failure at high temperature (( >100 Failure at high temperature >100 0C) 0C) Catalyst poisoning •• Catalyst poisoning •• High electro-osmotic drag High electro-osmotic drag There is a need to develop alternative advanced membranes based on aromatic hydrocarbons 6
  7. 7. Potential Polymer Architectures for PEM Materials F2 C CF2CF2 CFCF2 x OCF2CF Nafion CF3 x y OCF2CF2SO3H H2 C CH2 C CF2 CH2 ETFE-g-PSSA y z CH2 CH2 z SO3H SO3H Examples of PEMs O HO3S CF2 CF O C O CF2 CF n m n CH2CH CH2 CH R SO3H S-PEEK CH2 CH2 CH3 CH2 CH2CH BAM CH2 CH CH2CH3 S-SEBS SO3H SO3H 7
  8. 8. Microphase Separation in Block Copolymers F.S. Bates and G. H. Fredrickson, Physics Today, Feb. 1999. Block Copolymers Graft Polymers
  9. 9. Synthesis of Novel Fluoropolymer-blockIonic Polymers R-X x CF2=CH2 + y CF2=CF-CF3 Chain Transfer Radical Polymerization CH2CF2 x CF2CF y CF3 Macroinitiator R'-X n CuX / bpy CH2CF2 x CF2CF y CF3 CH2CH n X ATRP ClSO3H or CH3COOSO3H Sulfonation CH2CF2 x CF2CF y CF3 CH2CH n X SO3H • • • Chain Transfer Radical Emulsion Polymerization Atom Transfer Radical Polymerization Sulfonation 20%HFP 80%VDF HFP VDF
  10. 10. Synthesis of Fluorous-Ionic Graft Copolymer P(VDF-co-CTFE)-g-SPS x CF CH 2 2 + y CF 2 E m ulsion P olymerization CF * CH2CF2 Na S O + K S O 2 2 5 2 2 8 Cl 2.6mol%CTFE 97.4mol%VDF CuCl / bpy x CF2CF y CF2CF Cl P(VDF-co-CTFE)-g-PS * S ulfona tion z CH2CH Cl n * y P(VDF-co-CTFE) Macroinitiator n CH2CF2 CF2CF Cl AT R P * x CH3COOSO3H * CH2CF2 x CF2CF y CF2CF Cl * z CH2CH Cl n P(VDF-co-CTFE)-g-SPS SO3H 10
  11. 11. Membrane Morphology Diblock copolymer: H CH2CF2 x' Graft copolymer: CF2CF CH2CH y' n' CF3 CH2CF2 x CF2CF Cl y CF2CF z CH2CH SO3H n SO3H 100 nm Perforated Lamellar Morphology: - “Ionic” channels width = 8 – 15 nm 11 100 nm Disordered cluster-network Morphology: -Ionic cluster size = 2 – 3 nm Note: Nafion cluster size = 5 – 10 nm
  12. 12. Diblock vs Graft Membrane Diblock copolymer: Graft copolymer: 100 nm 100 nm - 120 90 60 30 0 0.08 0.06 0.04 0.02 0.00 0.0 0.5 1.0 1.5 2.0 2.5 IEC (mmol/g) Grafts (small ionic clusters): 0.0 0.5 1.0 1.5 2.0 IEC (mmol/g) - Less water swelling  Lower proton mobility - Maintain good mechanical property and high proton concentrations 2.5 1.2 2.5 1.0 2.0 0.8 1.5 0.6 1.0 0.4 0.5 0.2 0.0 x 103 (cm2 s-1 V-1) dissolves 150 3.0 eff Proton Conductivity (S/cm) 0.10 0.0 0.0 0.5 1.0 1.5 2.0 2.5 IEC (mmol/g) Diblocks (long-range channels): - Greater water uptake  Higher proton conductivity and mobility - Excessive water swelling  mechanical instability and limited attainable IEC. [H+] (M) H2O]/[SO3 ]) 180
  13. 13. 6-17% PS, Fully Sulfonated Proton Conductivity : 35% PS, p. Sulfonated (IONIC PURITY): 6-17% PS, Fully Sulfonated: 45% PS, p. Sulfonated B 50% PS, p. Sulfonated 100 nm 35% PS, Partially Sulfonated: E 100 nm 45% PS, Partially Sulfonated: H Proton Conductivity (S/cm) 0.12 6-17% PS, fully sulfonated 35% PS, partially sulfonated 45% PS, partially sulfonated 50% PS, partially sulfonated Nafion 117 0.10 0.08 0.06 0.04 0.02 0.00 100 nm 50% PS, Partially Sulfonated: 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IEC (mmol/g) J 100 nm - Fully sulfonated : continuous increase in proton conductivity with IEC - Partially sulfonated: initial increase followed 13 by drop in proton conductivity at high IEC.
  14. 14. Fluorinated polymer Partially Sulfonated polystyrene & water SANS: Contrast Variation Effect 100 nm Rubatat, Holdcroft, Diat, Shi. Frisken
  15. 15. Conclusions IEC = 0.70 mmol/g • • • • G K C 100 nm IEC = 0.68 mmol/g 100 nm IEC = 0.89 mmol/g 100 nm 500 nm Model fluorous-ionic diblock copolymers with different block ratios have been synthesized to investigate structure-property relationships in PEMs. Water sorption, proton conductivity, proton mobility, anisotropy, etc, depend strongly on the membrane morphology….and on the degree of sulfonation within an “ionic” channel. Ionic purity of the “ionic channel” is critical. The graft structure allows for very high IEC without dissolution – promising for low RH conductivity.
  16. 16. T.J. Peckham, S. Holdcroft. Adv. Mater., 22 (2010) 4667–4690 Yossef Elabd and Michael Hickner “Block Copolymers for Fuel Cells” Macromolecules, 2011, 44 (1), pp 1–11

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