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Nanotechnology in Hydrogen Fuel Cells

Nanotechnology in Hydrogen Fuel Cells . By Morten Bakker. "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009. Overview. Fuel cells Main concerns Nanotechnology applications. 2. "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009.

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Nanotechnology in Hydrogen Fuel Cells

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  1. Nanotechnology in Hydrogen Fuel Cells By Morten Bakker "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  2. Overview Fuel cells Main concerns Nanotechnology applications 2 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  3. William Robert Grove (1842) Fuel Cells: 815.000 hits (scholar.google) 2008: >1 billion US$ in FC research Fuel Cells 3 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  4. Working principle Electrochemical energy conversion Electrical current Oxidant (O2) H+ Fuel (H2) H+ Exhaust (H2O) Unused fuel Anode Electrolyte Cathode 4 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  5. Different types • Fuel: hydrocarbons (also alcohols), hydrogen, etc • Oxidant: chlorine, chlorine dioxides, oxygen, etc.. • Electrolyte: aqueous alkaline solution, polymer membrane, molten carbonate, ceramic solid oxide, etc.. • Operational temperature: 50°C - 1100°C 5 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  6. Advantages and Applications High efficieny energy conversion Theoretically 83% at 25°C High power density Reliable Compact Lightweight 6 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  7. Why Hydrogen Fuel Cells? • Also called Proton Exhange Membrane/ Polymer Electrolyte Membrane fuel cell (PEMFC) • Durable, compact • Low temperature (50°C -100°C), fast start-up • Hydrogen fuel economy • Especially transportation applications 7 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  8. Important components of PEMFC • Proton Exchange Membrane (PEM) • Electrodes (Catalysts) 8 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  9. Proton Exchange Membrane (PEM) • Conduct H+, but no e- • Ionomer • Polymer with ionic properties • Nafion • Teflon backbone with sulfonic groups The inventor of Nafion: Walther Grot (DuPont) 9 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  10. Transport through Membrane • Thin film (~20-100 µm) • Hydrated (depends on temperature) • Water channel model • Inverted-micelle cylinders • Ionic groups line up in water channel • Protons ‘hop’ from one acid site to another • Crystallites provide strength [Schmidt-Rohr, Chen, Nat Mat, 7, (2008), 75-83] 10 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  11. Challenges • Thermal balance: want to operate at higher temperature • Better cooling possible • Better heat recovery • Reduce CO poisoning (H2 reforming) US Dept. of Energy: 120°C • Problem: water management 11 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  12. Improving Conductivity • Add acidic nanoparticles (SiO2, TiO2, Zr(HPO4)2) • Increased water content • Improved proton conductivity • Operate at higher temperatures Current density (A cm-2) Cell resistance (Ω cm2) Temperature (°C) Voltage (V) [Baglio et al., Fuel Cells, (2008)] 12 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  13. Add Pt nanoparticles Not sustain water, but generate it: self-humidifying Pt-PDDA/ PTFE (Teflon)/ Nafion composite membrane Pt particles ~3 nm Permeating H2 and O2 generates water Voltage (V) [Liu et al., J. Membr. Sc., 330, 357-362, (2009)] Current density (A cm-2) 13 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  14. Electrodes • Consist of Carbon, with Platinum catalyst • Anode (H2): fast oxidation • Cathode (O2): slower reduction, critical component Disadvantages: • Cost • CO poisoning (H2 reforming) Reduce cost: increase Pt utilization 14 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  15. Nanoparticles High-surface area: Carbon powder or Carbon nanotubes Reduction of Pt-salt in solution Nanoparticles attached to C backbone [Liu et al., J. Pow. Sources, 139, 73-78, (2005)] 15 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  16. More advanced Nanostructures Activity = Surface x Surface reactivity Use other nanostructures. Nanoparticles Bulk Pt 16 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  17. Pt Nanowires 1-D nanowires Lower surface area, but increased activity Voltage (V) Current density (A cm-2) [Sun et al., Adv. Mat., 20, 3900-3904, (2008)] 17 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  18. Replace noble metals Replace electrode with Nitrogen-doped carbon nanotube arrays 18 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  19. Vertically aligned nitrogen-doped carbon nanotubes (VA-NCNT’s) Prepared by pyrolysis of iron (II) phthalocyanine plus NH3 vapour Self assembly on quartz substrate N2 induces increased O2 chemisorption [Gong et al., Science, 323, 760 (2009)] 19 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  20. Increased performance Increased catalysis (Air-saturated 0.1 M KOH) Pt: 1.1 mAcm-2 at -0.29 V VA-NCNT’s: 4.1 mAcm-2 at -0.22 V No CO poisoning High-surface area, good electrical, mechanical and thermal properties time (s) [Gong et al., Science, 323, 760 (2009)] 20 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  21. Summary Add nanoparticles to membrane Improved performance, operational temperature Increased cost Nanostructured Pt electrodes, N2 doped CNT’s Improved catalysis Decreased cost 21 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  22. Conclusions • Interesting and growing field of research • Nanotechnology essential for future developments • Problems: • Infrastructure (storage) • Sustainable H2 source 22 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

  23. Thank you for your attention! • I would like to especially thank Prof. Petra Rudolf • Questions? 23 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009

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