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
Hydrogen
Air or Oxygen
Load
Anode
Cathode
Electrolyte e-
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. Proton Exchange Membrane (PEM) solid polymer membrane hydrogen
Fuel Cell Type
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
pure oxygen
below 80°C
50–70%
Direct Methanol (DMFC)
methanol solution in water
atmospheric oxygen
35–40%
Phosphoric Acid (PAFC)
Phosphoric Acid
210°C (400°F)
35–50%
Molten Carbonate (MCFC)
Alkali- Carbonates
hydrogen, methane
650°C (1200°F)
40–55%
Solid Oxide (SOFC)
Ceramic Oxide
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.

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

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