Characteristics

Fuel cells structure

Fuel cells have a very simple structure. The cell itself consists of three layers, one above the other.  These are the anode, cathode and electrolyte.  The anode and cathode serve as a catalyst. The layer in the middle consists of a carrier structure which absorbs the electrolyte. In different types of fuel cells different substances are used as electrolyte.
Some electrolytes are liquid and some are solid with a membrane structure. Because one cell generates only low voltage several cells are stacked according to the requested voltage. This arrangement is called a "stack". 


 
What exactly does a fuel cell do?

The fuel cell reverses the process of electrolysis. In the process of electrolysis, by applying electric power, water is decomposed into its gaseous components of oxygen and hydrogen. 
The fuel cell takes these two substances and converts them into water again. In theory the same amount of energy which has been used for the electrolysis is set free by this conversion.  Electric power is stored in the hydrogen molecule.  In fuel cells we get back the electric power stored in the hydrogen. Most fuel cells operate with air, so there is no need to store oxygen.

The best-known fuel cell prototype which is still used today is the alkaline fuel cell (AFC).  It is the only type of fuel cell that requires oxygen and hydrogen in purest form because even small amounts of dirt would destroy the cell.  
AFCs have been used in manned space travel which would not have been possible without them. At the moment AFCs are in the development stage for the use as a mean of vehicle propulsion. But the fact that AFCs cannot be fed directly with air (but only with pure oxygen) is a big disadvantage. 
AFCs are especially suitable for niche vehicles because they can be produced quite cheaply, even in small numbers. An example of such an application are the famous London taxis.