Alkaline Fuel Cells – AFC
Apart from Grove's prototype the alkaline fuel cell - AFC - was the first type of fuel cell.
It was in use, and still is in use today, for space travel and submarine engines.
AFC is the only type of fuel cell that requires oxygen and hydrogen in purest form because even smallest amounts of dirt would destroy the cell. The electrolyte consists of caustic potash.
Today there are AFC available that can be operated with air. A very good filter is needed to clean the air to avoid contamination of the fuel cell.
The function of the fuell cell AFC
- 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 one electron.
- Step 3
The electrons move from the anode to the cathode and cause an electric current. This electric current supplies an electric capacitor with electric power.
- Step 4
Respectively four electrons recombine with one hydrogen molecule at the cathode.
- Step 5
The now generated oxygene ions react with water to OH ions.
- Step 6
This hydroxide ions move through the electrolyte (potash solution) to the anode.
- Step 7
The hydroxide ions react at the anode with the protons to water. The water is partly leaded back to the cathode to enhance the further reaction.
Alkaline fuel cells have been in use in manned space travel which would not have been possible without the fuel cell. In the Apollo and in the Apollo-Soyuz program as well as in the Skylab and in space shuttles alkaline fuel cells were and are in use.
At the moment AFCs are in the development stage for the use as vehicle drives. But the fact that AFCs can not be fed directly with air (but only with pure oxygen) is a big disadvantage.
CO2 has to be removed from the air in the beginning to avoid a 'poisoning' of the electrolyte. This requires additional devices in the fuel cell system.
Alkaline fuel cells are especially suitable for niche vehicles because they can be produced quite cheaply even in small numbers. An example for such an application are the famous London taxis.