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Introduction to Fuel Cells

Introduction to Fuel Cells. Hocking College Nelsonville Ohio July 24, 2007. Fuel Cells Generally Contain. Anode Anode Catalyst Cathode Cathode Catalyst Gas Diffusion Layer Electrolyte A load to complete the circuit Continuous feed of fuel Continuous feed of air or oxygen.

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Introduction to Fuel Cells

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  1. Introduction to Fuel Cells Hocking College Nelsonville Ohio July 24, 2007

  2. Fuel Cells Generally Contain • Anode • Anode Catalyst • Cathode • Cathode Catalyst • Gas Diffusion Layer • Electrolyte • A load to complete the circuit • Continuous feed of fuel • Continuous feed of air or oxygen

  3. Types of Fuel Cells • Fuel Cells are generally named by the electrolyte in the cell. • An exception to this is the methanol fuel cell, which is called the Direct Methanol Fuel Cell (DMFC).

  4. Types of fuel cells • PEM (polymer electrolyte membrane fuel cell) • DMFC (polymer electrolyte membrane fuel cell) • SOFC (solid oxide fuel cell) • MCFC (molten carbonate fuel cell) • AFC (alkaline fuel cell) • PAFC (phosphoric acid fuel cell)

  5. Load e- Air or Oxygen Fuel Hydrogen Anode Cathode Electrolyte A Fuel Cell Converts Chemical Energy to Electrical Energy Gas Diffusion Layer Gas Diffusion Layer H+ Catalyst Catalyst

  6. The Electrical Energy is in the form of DC voltage • The voltage is usually between 0.5 and 1.0 volts DC (direct current). • Several fuel cells are connected together in series to obtain higher voltages 25—100 volts. • These fuel cells connected in series are called stacks. • The fuel cell stacks still give DC voltage.

  7. An Inverter is used to change the DC voltage to AC voltage (alternating current). • Direct Current (DC) has a voltage that is always in one direction. • DC voltage is the kind of voltage that comes from a battery. • Alternating Current (AC) has a voltage that varies from positive to negative 60 times/second (50 times/second in Europe). • Normal household current is AC.

  8. Fuel CellType Electrolyte Anode Gas Cathode Gas Temperature Efficiency Proton Exchange Membrane(PEM) solid polymer membrane hydrogen pure or atmospheric oxygen 75°C(180°F) 35–60% Alkaline(AFC) potassium hydroxide hydrogen pureoxygen below80°C 50–70% Direct Methanol(DMFC) solid polymer membrane methanol solution in water atmosphericoxygen 75°C(180°F) 35–40% Phosphoric Acid(PAFC) Phosphoric Acid hydrogen atmosphericoxygen 210°C(400°F) 35–50% Molten Carbonate(MCFC) Alkali-Carbonates hydrogen,methane atmosphericoxygen 650°C(1200°F) 40–55% Solid Oxide(SOFC) Ceramic Oxide hydrogen,methane atmosphericoxygen 800–1000°C(1500–1800°F) 45–60%

  9. Each type of fuel cell is particularly suited to certain applications: • PEM: most versatile, used for portable power, transportation, and stationary power • DMFC: used for portable power • SOFC: primarily used for stationary power, in development for transportation (e.g. semi trucks) • MCFC: power plants • AFC: power and water production for space vehicles (e.g. Apollo and Space Shuttle spacecrafts), in development for more general use • PAFC: stationary power, power plants

  10. Each type of fuel cell has particular advantages and disadvantages • PEM & DMFC: solid construction, low temperature, sensitive to impurities, can only be used with hydrogen or methanol. • SOFC: can be used with many fuels, doesn’t require precious metal catalysts, solid, rugged, very high temperature, expensive materials. • MCFC: can be used with many fuels, efficient, doesn’t require precious metal catalysts, high temperature, very corrosive electrolyte. • AFC: most efficient medium for oxygen reaction - high performance, doesn’t require precious metal catalysts, sensitive to carbon dioxide, caustic medium. • PAFC (phosphoric acid fuel cell): same electrochemical reactions as PEM, but not as sensitive to impurities in the fuel, very corrosive.

  11. Advantages • PEM & DMFC: solid construction, low temperature • SOFC: can be used with many fuels, doesn’t require precious metal catalysts, solid, rugged, very high temperature (high enough for power generation)

  12. Advantages • MCFC: can be used with many fuels, efficient, doesn’t require precious metal catalysts, high temperature (high enough for power generation) • AFC: most efficient medium for oxygen reaction - high performance, doesn’t require precious metal catalysts • PAFC (phosphoric acid fuel cell): same electrochemical reactions as PEM, but not as sensitive to impurities in the fuel

  13. Disadvantages • PEM & DMFC: low temperature (low grade energy), must have pure hydrogen. • SOFC: very high temperature, expensive materials. • MCFC: liquid, high temperature , very corrosive electrolyte • AFC: liquid, sensitive to carbon dioxide, caustic medium, low temperature (low grade heat) • PAFC: liquid, very corrosive, low temperature, (low grade heat)

  14. Typical fuel cells run on hydrogen and oxygen • Methane, methanol, and other hydrogen containing compounds can be reformed to make hydrogen. • Air is usually used instead of pure oxygen.

  15. PEM Fuel Cell Cathode Backing Anode Backing Anode Flowfield (hydrogen) Cathode Flowfield (oxygen) PEM Pt Catalyst Pt Catalyst

  16. Source: Thampan, PEM Fuel Cell as a Membrane Reactor

  17. PEM or DMFC Fuel Cell Components • CCM (Catalyst Coated Membrane): Proton-conducting membrane plus 2 electrodes • GDL (Gas Diffusion Layer): Carbon cloth or paper with carbon particle filler and Teflon • Anode and Cathode plate: Graphite, carbon composite or metal with machined or stamped ‘flow field’ • Gaskets and seals: seals around edge of structure

  18. SOFC Componets • Anode:Ni/YSZ Cermet • Electrolyte:Yttrium Stabilized Zirconia (YSZ) • Cathode: Lanthanum Strontium Manganite (LSM)

  19. MCFC Components • Anode is a highly porous sintered nickel powder, alloyed with chromium • Electrolyte is a liquid in a lithium—Aluminum Oxide matrix • Cathode is a porous nickel oxide material doped with lithium.

  20. AFC Components • Electrodes: >porous (and catalyzed) graphite electrodes >semi-permeable, Teflon coated carbon material >heavily catalyzed as compared with other types of fuel cells • Electrolyte: potassium hydroxide (KOH) solution retained in a porous stabilized matrix

  21. PAFC Components • Electrodes: porous carbon containing Pt or its alloys as catalysts • Electrolyte: liquid phosphoric acid in Teflon-bonded silicon carbide matrix

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