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Hydrogen fuel cells

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Hydrogen fuel cells

  1. 1. HYDROGEN FUEL CELLS Karen Wang Joey Liu
  2. 2. Connections <ul><li>Hydrogen Fuel Cells and Re - dox Reactions </li></ul><ul><li>Alkaline Fuel Cells </li></ul><ul><li>Hydrogen Fuel Cells and Electrochemistry & thermodynamics </li></ul><ul><ul><li>Catalyst, anodes, cathodes </li></ul></ul><ul><li>Temperature & efficiency of Hydrogen Fuel Cells </li></ul><ul><li>5.4 Hydrogen Fuel Cells and the Environment </li></ul><ul><li>Applications of Hydrogen Fuel Cells– nuclear energy </li></ul>
  3. 3. INTRODUCTION Fuel Cell Overview
  4. 4. Historical Overview <ul><li>1838: discovered by German scientist Christian Friedrich Schöenbein </li></ul><ul><li>1839: Demonstrated by Welsh scientist Sir William Robert Grove </li></ul>
  5. 5. What are Fuel Cells? <ul><li>Battery that produces electricity </li></ul><ul><li>overall reaction: oxidation of a fuel by oxygen </li></ul><ul><li>2H 2(g) + O 2(g)  2H 2 O (l) </li></ul><ul><li>(Hydrogen) Fuel + oxygen  water </li></ul><ul><li>Unlimited fuel supply: reactants continuously supplied from an external source (open system) </li></ul><ul><ul><li>Also known as flow battery </li></ul></ul><ul><li>Used as a stack </li></ul>
  6. 6. Types of Fuel Cells <ul><li>Molten carbonate cells </li></ul><ul><li>Solid oxide cells </li></ul><ul><li>Direct methanol and other non-hydrogen cells </li></ul><ul><li>Biofuel cells </li></ul><ul><li>Phosphoric Acid </li></ul><ul><li>Proton Exchange Membrane </li></ul><ul><li>Acid and alkaline cells </li></ul>
  7. 7. How Do Fuel Cells Work? HYDROGEN FUEL CELLS & ELECTROCHEMISTRY
  8. 8. Connection 1: FUEL CELLS & REDOX REACTION <ul><li>oxidation </li></ul><ul><ul><li>Anode (negative electrode): e- leave the cell </li></ul></ul><ul><ul><li>H 2  2H + + 2e - </li></ul></ul><ul><li>reduction </li></ul><ul><ul><li>Cathode (positive electrode): e- enter the cell </li></ul></ul><ul><ul><li>4H + + 4e - + O 2  2H 2 O </li></ul></ul>
  9. 9. Connection 2: FUEL CELLS & CATALYSTS (rate of reaction) <ul><li>the splitting of H2 into p+ and e- at the a node is typically speeded up by the presence of a catalyst (typically metal placed on the anode, or the electrode itself) </li></ul><ul><li>Platinum film is often used </li></ul>
  10. 10. <ul><li>Electrolyte – permit only appropriate ions to pass between anode and cathode; otherwise the chemical reaction may be disrupted </li></ul><ul><li>End product: water = drained </li></ul>
  11. 11. Types of Fuel Cells Connection 3 HYDROGEN FUEL CELLS ALKALINE & PEM FUEL CELLS
  12. 12. TYPES OF HYDROGEN FUEL CELLS <ul><li>Alkaline Fuel Cells </li></ul><ul><li>Aka: Bacon fuel cell </li></ul><ul><li>Used in NASA since mid-1960s (Appollo) </li></ul><ul><li>Efficiency – 70% </li></ul><ul><li>hydrogen + oxygen  water, heat, electricity </li></ul><ul><li>PEM Fuel Cells </li></ul><ul><li>Proton Exchange Membrane (or Proton Electrolyte Membrane) </li></ul><ul><li>Transport applications and stationary fuel cell applications </li></ul><ul><li>Lower temp./pressure ranges (50-100℃) </li></ul>
  13. 13. Alkaline Fuel Cells <ul><li>Hydrogen </li></ul><ul><li>Electron flow </li></ul><ul><li>Load </li></ul><ul><li>Oxygen </li></ul><ul><li>Cathode </li></ul><ul><li>Electrolyte </li></ul><ul><li>Anode </li></ul><ul><li>Water </li></ul><ul><li>Hydroxyl ions </li></ul>
  14. 14. How Hydrogen Fuel Cells Work – PEM <ul><li>Proton exchange membrane cells </li></ul><ul><li>A fuel cell produced electricity by combining Hydrogen and Oxygen atoms electrochemically rather than through combustion </li></ul><ul><li>Hydrogen = fuel  electrolysis – stored as a compressed gas/liquid/metal compound </li></ul><ul><li>A single fuel cell consists of an anode and a cathode with an electrolyte in between </li></ul><ul><li>Hydrogen molecules enter the anode  react with catalysts (1)  split into H+ & e-  H+ pass through electrolyte, e- directed through an external circuit = electrical current </li></ul><ul><li>Oxygen molecules enter at the cathode + H + + e-  water & heat </li></ul><ul><li>Individual fuel cells placed in a series = fuel cell stack  power vehicle </li></ul>
  15. 17. HYDROGEN FUEL CELLS & REDOX REACTION <ul><li>Alkaline Fuel Cells </li></ul><ul><li>@ Anode, H2 is oxidized: </li></ul><ul><li>H 2 + 2OH -  2H 2 O + 2e - H 2  2H + + 2e - </li></ul><ul><li>Electrons flow through an external circuit and return to the cathode, reducing oxygen: </li></ul><ul><li>O 2 + 2H 2 O + 4e -  4OH - 4H + + 4e - + O 2  2H 2 O </li></ul><ul><li>PEM Fuel Cells </li></ul>
  16. 18. HYDROGEN FUEL CELLS AS AN ENERGY SOURCE
  17. 19. Connection 4 : HYDROGEN FUEL CELLS & EFFICIENCY and THERMODYNAMICS <ul><li>Automobile internal combustion engines </li></ul><ul><ul><li>inefficient – 25% </li></ul></ul><ul><li>Rechargeable batteries (modified lead-acid, nickel-cadmium batteries) </li></ul><ul><ul><li>Run down quickly – 250 Km </li></ul></ul><ul><ul><li>Recharged from external electrical source </li></ul></ul><ul><ul><li>Takes hours </li></ul></ul><ul><li>Fuel cells </li></ul><ul><ul><li>Efficient – 80% </li></ul></ul>
  18. 20. Connection 4 : HYDROGEN FUEL CELLS & EFFICIENCY and THERMODYNAMICS <ul><li>Fuel cells create electricity chemically; unlike combustion, are not subject to thermodynamic laws </li></ul><ul><li>∴ fuel cells are more efficient </li></ul><ul><ul><li>Some waste heat can also be harnessed </li></ul></ul>
  19. 21. Connection 5: HYDROGEN FUEL CELLS & THE ENVIRONMENT <ul><li>Automobile engines: gasoline = pollutants </li></ul><ul><ul><li>CO 2 , No x , VOCs </li></ul></ul><ul><ul><li>health & environmental problems: smog, greenhouse effect </li></ul></ul><ul><li>Electric cars: hydrogen fuel cells = pollution free </li></ul><ul><ul><li>Cleaner, quieter, more efficient </li></ul></ul><ul><ul><li>Product: water vapour </li></ul></ul>
  20. 22. Connection 5: HYDROGEN FUEL CELLS & THE ENVIRONMENT <ul><li>Production of hydrogen fuel – unnatural resource </li></ul><ul><ul><li>Hydrocarbon fuels (petroleum, methane) = pollution </li></ul></ul><ul><ul><li>Electrolysis of water powered by solar energy or hydroelectricity = low pollution </li></ul></ul><ul><li>Renewable energy source </li></ul>
  21. 23. systems <ul><li>Fuel cell powered cars </li></ul><ul><ul><li>http:// www.youtube.com/watch?v =oy8dzOB-Ykg </li></ul></ul><ul><ul><li>Efficiency, pollution-free </li></ul></ul>
  22. 24. Connection 6: HYDROGEN FUEL CELLS AS AN ENERGY SOURCE <ul><li>Production of hydrogen fuel – unnatural resource </li></ul><ul><ul><li>Hydrocarbon fuels (petroleum, methane) = pollution </li></ul></ul><ul><ul><li>Electrolysis of water powered by solar energy or hydroelectricity = low pollution </li></ul></ul>
  23. 25. Connection 6: HYDROGEN FUEL CELLS & NUCLEAR ENERGY <ul><li>Implementation scenarios </li></ul><ul><ul><li>Fossil </li></ul></ul><ul><ul><li>nuclear </li></ul></ul>
  24. 26. References <ul><li>(Sørensen), B. S. (2005). Hydrogen and Fuel Cells: Emerging Technologies and Applications (Sustainable World) . Toronto: Academic Press. </li></ul><ul><li>Harkin, T., & Hoffmann, P. (2001).  Tomorrow's Energy: Hydrogen, Fuel Cells, and the Prospects for a Cleaner Planet . London: The Mit Press. </li></ul><ul><li>Holland, G., & Provenzano, J. (2007).  Hydrogen Age, The . Layton: Gibbs Smith, Publisher. </li></ul><ul><li>ollecting the History of Proton Exchange Membrane Fuel Cells. (n.d.).  National Museum of American History . Retrieved April 20, 2010, from http://americanhistory.si.edu/fuelcells/basics.htm </li></ul>

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