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

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Presentation on theme: "Introduction to Fuel Cells Hocking College Nelsonville Ohio July 24, 2007."— Presentation transcript:

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

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 Cell Type ElectrolyteAnode GasCathode GasTemperatureEfficiency Proton Exchange Membrane (PEM) solid polymer membranehydrogenpure or atmospheric oxygen 75°C (180°F) 35–60% Alkaline (AFC) potassium hydroxidehydrogen pure oxygen below 80°C 50–70% Direct Methanol (DMFC) solid polymer membranemethanol solution in water atmospheric oxygen 75°C (180°F) 35–40% Phosphoric Acid (PAFC) Phosphoric Acidhydrogen atmospheric oxygen 210°C (400°F) 35–50% Molten Carbonate (MCFC) Alkali- Carbonates hydrogen, methane atmospheric oxygen 650°C (1200°F) 40–55% Solid Oxide (SOFC) Ceramic Oxide hydrogen, methane atmospheric oxygen 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.

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

17 Source: Thampan, PEM Fuel Cell as a Membrane Reactor

18 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

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

20 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.

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

22 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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