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Fuel Cells

NREL. Fuel Cells. San Jose State University FX Rongère March 2009. Definition. Electrochemical device converting directly chemical energy in electricity Different from an engine since no conversion in heat as an intermediate

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Fuel Cells

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  1. NREL Fuel Cells San Jose State University FX Rongère March 2009

  2. Definition • Electrochemical device converting directly chemical energy in electricity • Different from an engine since no conversion in heat as an intermediate • Different from a battery since continuous flow of fuel and oxidant

  3. History • First fuel cell built in 1839 by Sir William Grove. • Advances by Mond and Langer (1889), Thomas Bacon (1932) and Harry Ihrig, who produced a 20 hp fuel cell tractor • Serious interest began in the 1960’s with the U.S. space program • Gemini and Apollo spacecraft • Space Shuttle From ME200_2005

  4. Fuel Cell vs Thermal Engine • Thermodynamic Maximum Conversion Rate • Thermal Engine (Carnot Law) • Fuel Cell (Free Energy law) G: Gibbs free Energy=Free Enthalpy

  5. Thermodynamics • Balance equations

  6. Materials Properties • At 25oC and 1 atm

  7. Electric Potential V: Electric Potential through the cell (Volts) N: Number of electrons transferred E: Electric charge of an electron (Coulomb) For a perfect cell at 25oC: ΔG = -237 kJ/mol N = 2 . A A= 6.02 10-23 mol-1 e = 1.602 10-19 Coulomb V = 1.23 Volts Then:

  8. Principle Load e- Fuel in Oxidant in O2 H2 H+ H2 H2O Anion O2 H2O Conductor ½ O2- Electrolyte (Ionic conductor) Depleted oxidant Depleted fuel Anode Cathode Source: Meilin Liu Fuel Cell Technology Status, Challenges, and Opportunities Georgia Tech 2000

  9. Types of Fuel Cells • Many types of fuel-cells fitting different applications Transportation Portable Devices Stationary

  10. Proton Exchange Fuel Cells Source: http://www.fueleconomy.gov/feg/fcv_pem.shtml)

  11. Actual Conversion Rate • Theoretical maximum conversion rate: • Additional losses: • Kinetic losses • Ohmic losses • Mass transport losses

  12. PEMFC Challenges and Applications • Challenges: • Catalyst: platinum is rare and expensive • Requires high purity hydrogen, CO and other pollutants degrade the catalyst • Requires very accurate control of the humidity of the membrane (80%) • Life duration is still low • Hydrogen infrastructure • Cost • Applications: • Transportation

  13. Solid Oxyde Fuel Cells (Porous perovskite ) Porous nickel-cermet (Solid Oxide)

  14. SOFC Materials • The anode and cathode are porous while the electrode is dense • The anode and cathode are porous to allow the air and fuel in • The electrolyte is dense to prevent the air and fuel from mixing

  15. SOFC Materials • The most common electrolyte material is ZrO2 (zirconia) doped with Y2O3 (yttria). This material is known as yttria-stabilized zirconia (YSZ). This is a ceramic material - a compound of a metal with a non-metal. • Ni/YSZ cermet (ceramic-metal composite) is used as the anode material because of its low cost. It is also chemically stable at high temperatures and its thermal expansion coefficient is close to that of the YSZ electrolyte. • The cathode is based on an alloy (La1-ySry) MnO3-d (LSM) with a perovskite crystal structure

  16. Periodic Table

  17. Conversion Rate • Schematic of energy flow in a SOFC Source: Jens Pålsson, John Bøgild Hansen , Niels Christiansen, Jens Ulrik Nielsen, Steen Kristensen Solid Oxide Fuel Cells – Assessment of the Technology from an Industrial Perspective

  18. SOFC Challenges and Applications • Advantages: • Accept concentration of CO • Low pollution (NOx) • Low noise • Challenges: • High Temperature • Cost $4,000/kWe • Sensitive to H2S (<1ppmv) • Applications: • Stationary generators • Pilots on land fills and dairies

  19. Companies to follow • www.bloomenergy.com • www.acumentrics.com • www.ballard.com • www.idatech.com • www.lynntech.com • www.plugpower.com • www.siemens.com • www.hitachi.com • www.toyota.com • www.utc.com • www.fuelcells.org

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