Hydrogen / Fuel Cells
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Virtual Exhibition


BetrSichV 3

Phosphoric Acid Fuel Cell – PAFC


The PAFC is the type of fuel cell which has reached the highest stage of technological and commercial development. Because it is run at a high operating temperature it is suited perfectly for cogeneration. Highly concentrated phosphoric acid which is bond in a gel matrix serves as catalyst.

The PAFC requires atmospheric oxygen and hydrogen as reduction gases. One disadvantage is that the phosphoric acid effloresces irreversibly when temperature sinks below 42°. When this happens the fuel cell becomes unusable.

The function of the PAFC

  • Step 1
    Inside the two seperate gas supply cicuits the gaseous oxygene and hydrogen flow into the gas area and the catalyzer.
  • Step 2
    While getting in contact with the catalyzer the hydrogen molecules (H2) are splitted into two H+ protons. At the same time each hydrogen atom sends out an electron.
  • Step 3
    The protons move through the electrolyte (highly concentrated phosphoric acid) to the cathode area
  • Step 4
    The electrons move into the anode and cause an electric current. This electric current supplies an electric capacitor with electric power.
  • Step 5
    Respectively four electrons recombine with one hydrogen molecule at the cathode.
  • Step 6
    The now generated oxygene ions have a negative load. They now move to the positiv loaded protons.
  • Step 7
    The oxygene ions give their electrons to the two protons and oxidize with them to water.


Applications for the PAFC

The PAFC is used exclusively for the cogeneration of power and heat.

The PAFC was the first commercially available fuel cell. In units with an electric power of 200 kW and a thermal power of 220 kW it is offered by the American company ONSI. Up to now more then 200 PAFC plants have been installed world-wide.