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Department of Chemical and Materials Engineering Chang Gung University, Taiwan

Electrospun quaternized polyvinyl alcohol nanofibers with core-shell structure and their composite in alkaline fuel cell application. Department of Chemical and Materials Engineering Chang Gung University, Taiwan. S. Jessie Lue, Ph.D. Department Head and Professor. Research focuses.

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Department of Chemical and Materials Engineering Chang Gung University, Taiwan

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  1. Electrospun quaternized polyvinyl alcohol nanofibers with core-shell structure and their composite in alkaline fuel cell application Department of Chemical and Materials Engineering Chang Gung University, Taiwan S. Jessie Lue, Ph.D. Department Head and Professor

  2. Research focuses Fuel cell Solar cell Lithium–air battery Energy Water treatment Biomaterials Thermo-responsive biomaterials Thin film composite Prepare and synthesize frontier materials for energy, water treatment, and biomedicine applications

  3. Fuel cells using proton exchange membranes http://en.wikipedia.org/wiki/Fuel_cell Anode: H2 → 2 H+ + 2 e- Cathode: 1/2 O2 + 2 H+ + 2 e- → H2O Overall: H2 + 1/2 O2 → H2O, Eo= 1.2 V CH3OH + 3/2 O2 → CO2 + 2 H2O Eo= 1.21 V • Limitations: • Methanol cross-over • - Fuel loss • - Mixed cell potential • Expensive Pt based catalyst • Proton exchange membrane • Drawbacks: • H2 explodes easily • Complex system, requires large footprint Lue et al., J. Membr. Sc. 367 (2011) 256–264. Piela and Zelenay, The Fuel Cells Review 1 (2004) 17–23.

  4. Direct methanol fuel cell (DMFC) applications QBEAK DMFC car Yamaha DMFC scooter Toshiba DMFC external power EFOY DMFC generators 

  5. Hydroxide-conducting electrolytes for DMAFCs • Advantages: • Faster methanol oxidation rate in alkaline media • Less expensive non-Pt catalysts • Direction of OH− anion motion opposes methanol permeability: less MeOH cross-over • Easy water manegement • Yu and Scott, J. Power Sources 137 (2004) 248–256. CH3OH + 3/2 O2 → CO2 + 2 H2O Eo= 1.21 V, ΔGo= -702 kJ mol–1 • Challenges: • High ionic conductivity • Low methanol permeability Lue et al., J. Membr. Sci. 367 (2011) 256–264.

  6. Hydroxidetransport mechanisms Vehicular diffusion Hopping mechanism Surface diffusion Polymer w/anion-exchange moiety Polymer containing carbon nano-tubes Polymer free volume

  7. Membrane electrolyte development strategy: Q-PVA/Q-chitosan Semi-crystalline PVA/fumed silica Blend with nanoparticles Blend with Q-chitosan nanoparticles Polymer 50 (2009) 654 J Membr Sci 325 (2008) 831 J Membr Sci 367 (2011) 256 J Power Sources 195 (2010) 7991 PVA/Fe3O4-CNT Nafion/GO PVA/CNT PBI/CNT J Polym Sci Phys 51 (2013) 1779 J Membr Sci 376 (2011) 225 J Power Sources 202 (2012) 1 J Power Sources 246 (2014) 39 J Membr Sci 444 (2013) 41 J Membr Sci 485 (2015) 17

  8. Electrospun nanofiber for fuel cell review OH • Lower methanol permeability than the recast film by Li et al. (J. Membr. Sci., 2014) and Lin et al. (J. Membr. Sci., 2014). • Higher ionic conductivity than commercial film by Dong et al. (Nano Lett., 2010). • Pmax = 72.9 mW cm-2 at 70ºC Nafion/Nafion nanofiber in 2 M methanol by Li et al. (J. Membr. Sci., 2014). Proposed ion conduction mechanisms: PVA CNT SO3- SO3- SO3- H+ H+ Inorganic electrospun sulfonated zirconia fiber SO3- SO3- SO3- H+ H+ Anisotropic ionic aggregates in Nafion nanofiber (Yao et al., Electrochem. Commun., 2011.) Dong et al., Nano Lett., 2010. Pan et al., J. Power Sources, 2012.

  9. Objectives • Prepare Q-PVA electrospun nanofibers and Q-PVA composite membranes • Characterizations of nanofiber mat and composite membranes • Correlate cell performance with membrane properties • Elucidate ion conduction mechanism

  10. Preparation of Q-PVA electrospun nanofiber mat and composite membrane http://www.materialsnet.com.tw/DocView.aspx?id=9829 Nanofiber embedded in Q-PVA solution Q-PVA PVA Electrospun Q-PVA 6 wt% nanofiber mat in Q-PVA

  11. Single cell assembly and test MEA (membrane electrode assembly) Anode (catalyst on gas diffusion electrode): Pt-Ru/C on carbon cloth Membrane electrolyte Cathode (catalyst on gas diffusion electrode): PT/C on carbon cloth

  12. Characteristics of Q-PVA electrospun nanofiber mat Mean pore size= 195±20 nm Porosity = 71% Q-PVA Electrospun Q-PVA nanofiber mat Crystallinity ↓ and conductivity ↑ during electrospinning.

  13. Comparison of Q-PVA and Q-PVA electrospun nanofiber mat . electrospun Q-PVA nanofiber amorphous region stained by uranyl acetate Crystallinity ↓, density ↓ and FFV ↑ in electrospun nanofibers

  14. Morphology of Q-PVA composite membrane Top surface Electrospun Q-PVA Cross-section 50 µm 6 wt% nanofiber mat in Q-PVA

  15. MeOH permeability of Q-PVA composite membrane Methanol solution Pure water Diffusion cell Unit: ×10−6 cm2 s-1 Suppress methanol permeability dramatically

  16. Ionic conductivity of Q-PVA composite membrane membrane AC impedance test instrument T tube Unit: ×10−2 S cm-1 Ea: activation energy in Arrhenius equation Enhance ionic conductivity and lower activation energy

  17. Super ionic pathways in Q-PVA composite Inner diffusion Surface diffusion • Increase OH– permeation: -polymeric free volume -super ionic pathway • Decrease methanol permeation: -larger than OH– -more tortuous path Q-PVA electrospun nanofibers Functionalized carbon nanotubes

  18. Cell performance 53 mW cm–2 Long-term cell test 47 mW cm–2 At 60ºC At 60ºC 190 mA cm−2 with a 30-min off-period every 20 h 2 M methanol in 6 M KOH • Increased cell performance by embedding nanofiber mat in Q-PVA • Q-PVA composite possesses durability in DMFC test

  19. Conclusion • Super-conductive coaxial Q-PVA nanofibers are prepared by electrospinning method.  • Q-PVA composite containing Q-PVA nanofibers suppressed methanol permeability.   • Nanofiber core exhibited amorphous region and formed super ionic conductive path.  • Q-PVA composite is an effective electrolyte and validated using alkaline fuel cell.

  20. Acknowledgements • Ministry of Science and Technology, Taiwan • Chang Gung Hospital Project • Prof. Ying-Ling Liu (National Tsing Hua University) • Prof. Chun-Chen Yang (Ming Chi University of Technology) • Mr. Guan-Ming Liao, Ms. Pin-Chieh Li, Ms. Jia-Shiun Lin, Dr. Hsieh-Yu Li, Dr. Chao-Ming Shih, Dr. Rajesh Kumar

  21. Introducing anion-exchange groups Quaternized polymer matrix and nano-particles Insoluble in hot water Average particle size: 400 nm Crosslinked Q-PVA Q-PVA/5% Q-Chitosan

  22. Diffusivity enhancement at higher particle loading: positive correlation with FFV Semi-crystalline 500 nm Blend with nanoparticles More amorphous region (Lue et al., J. Membr. Sci. 325 (2008) 831)

  23. Material synthesis PVA O3 MWCNT 80C drying Add f-CNT (0.025-0.1%) into PVA solution Casting and drying

  24. Improvement with CNT containing Fe3O4nano-particles PVA-CNT(Fe3O4) composites OH PVA (Lo et al., J. Membr. Sci. 444 (2013) 41)

  25. Anode:3020loading 2 mg cm-2 Cathode:4020 loading 1 mg cm-2 Pt-based catalysts Non-Pt catalysts 2 M MeOH Pt vs. non-Pt catalysts 3 M EtOH Q-PVA/Q-chitosan electrolyte

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