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 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 2

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

4. Working principle AnodeElectrolyteCathode Fuel (H 2 ) Unused fuel Oxidant (O 2 ) Exhaust (H 2 O) H+H+ H+H+ Electrical current "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 4 Electrochemical energy conversion

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 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 5

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

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 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 7

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

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) "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 9

10. Transport through Membrane  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]  Thin film (~20-100 µm)  Hydrated (depends on temperature) "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 10

11. Challenges  Thermal balance: want to operate at higher temperature  Better cooling possible  Better heat recovery  Reduce CO poisoning (H 2 reforming) US Dept. of Energy: 120°C  Problem: water management "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 11

12. Improving Conductivity  Add acidic nanoparticles (SiO 2, TiO 2, Zr(HPO 4 ) 2 )  Increased water content  Improved proton conductivity  Operate at higher temperatures "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 12 [Baglio et al., Fuel Cells, (2008)]Temperature (°C) Cell resistance (Ω cm 2 ) Voltage (V) Current density (A cm -2 )

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

14. Electrodes  Consist of Carbon, with Platinum catalyst  Anode (H 2 ): fast oxidation  Cathode (O 2 ): slower reduction, critical component Disadvantages:  Cost  CO poisoning (H 2 reforming) Reduce cost: increase Pt utilization "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 14

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)] "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 15

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

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

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

19. Vertically aligned nitrogen-doped carbon nanotubes (VA-NCNT’s)  Prepared by pyrolysis of iron (II) phthalocyanine plus NH 3 vapour  Self assembly on quartz substrate  N 2 induces increased O 2 chemisorption [Gong et al., Science, 323, 760 (2009)] "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 19

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 [Gong et al., Science, 323, 760 (2009)] "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 20 time (s)

21. Summary  Add nanoparticles to membrane  Improved performance, operational temperature  Increased cost  Nanostructured Pt electrodes, N 2 doped CNT’s  Improved catalysis  Decreased cost "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 21

22. Conclusions  Interesting and growing field of research  Nanotechnology essential for future developments  Problems:  Infrastructure (storage)  Sustainable H 2 source "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 22

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