How Fuel Cells Work

There are several different types of fuel cells that work with different electrochemical reactions. The types of fuel cells have very technical names (abbreviated as shown) and are:

  •  Proton Exchange Membrane (PEM)
  •  Phosphoric Acid (PAFC)
  •  Solid Oxide (SOFC)
  •  Alkaline (AFC)
  •  Direct Methanol (FMFC)
  •  Molten Carbonate (MCFC)

The Proton Exchange Membrane is one of the most commonly used types of fuel cells and is very promising for widespread use in homes and automobiles. The Alkaline fuel cell is the oldest design. It has been used in the U.S. space program since the 1960s, but is quite expensive and probably least likely to be used in homes.

The chemical elements used in a fuel cell are:

  •  Hydrocarbons (natural gas) (CH2)
  •  Oxygen (O2)
  •  Water (H2O)
  •  Hydrogen (H2)
  •  Carbon Dioxide (CO2)
  •  Carbon Monoxide (CO)

And the hardware elements are the:

  •  Fuel Processor or Reformer
  •  Fuel Cell
  •  Converter

For this example, the Proton Exchange fuel cell will be used.

1. Hydrocarbons, water and oxygen are processed through a fuel processor (also called a reformer) to produce hydrogen, carbon dioxide and carbon monoxide.

2. Water is added and carbon monoxide is converted to carbon dioxide plus hydrogen.

The hydrogen produced is then ready for conversion in the fuel cell itself, which consists mainly of two electrodes- the negative anode and the positive cathode- separated by an electrolyte- in this case a polymer electrolyte membrane (PEM). The electrodes are coated on one side with a catalyst that helps the process. The catalyst is a special material that facilitates the reaction of oxygen and hydrogen.

3. Pressurized hydrogen fuel enters the anode side and air enters the cathode side. With the help of the catalyst, the hydrogen molecule splits into two protons and two electrons. The hydrogen has a negative and positive charge like a battery.

4. As the hydrogen molecules enter the negative electrode, they split in two, forming protons and electrons.

5. The hydrogen enters the fuel cell where the electrons (negative charge) flow out of the fuel cell as electricity. The protons (positive charge) travel across the PEM and combine with oxygen from the air.

6. This chemical reaction creates molecules of water that leave the fuel cell and generate heat, as well as supply the positive side needed to complete the electrical circuit.