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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 Fuel Cells William Robert Grove (1842) 3 Fuel Cells: 815.000 hits (scholar.google) 2008: >1 billion US$ in FC research "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 Working principle Electrochemical energy conversion Electrical current Fuel (H2) H+ Oxidant (O2) H+ Unused fuel 4 Anode Electrolyte Cathode "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 Exhaust (H2O) 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 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 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 Important components of PEMFC Proton Exchange Membrane (PEM) Electrodes (Catalysts) 8 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 Proton Exchange Membrane (PEM) Conduct H+, but no eIonomer 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 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 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 Improving Conductivity Add acidic nanoparticles (SiO2, TiO2, Zr(HPO4)2) Increased water content Improved proton conductivity Operate at higher temperatures Cell resistance (Ω cm2) Current density (A cm-2) Temperature (°C) 12 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 Voltage (V) [Baglio et al., Fuel Cells, (2008)] 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)] 13 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 Current density (A cm-2) 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 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 More advanced Nanostructures Activity = Surface x Surface reactivity Nanoparticles Bulk Pt Use other nanostructures. 16 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 Pt Nanowires Voltage (V) 1-D nanowires Lower surface area, but increased activity 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 Replace noble metals Replace electrode with Nitrogen-doped carbon nanotube arrays 18 "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 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 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 Summary Add nanoparticles to membrane Improved performance, operational temperature Increased cost Nanostructured Pt electrodes, N2 doped CNT’s 21 Improved catalysis Decreased cost "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 Conclusions Interesting and growing field of research Nanotechnology essential for future developments Problems: 22 Infrastructure (storage) Sustainable H2 source "Energy & Nano" - Top Master in Nanoscience Symposium 17 June 2009 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