Fuel Cell Types:

The fuel cell is in principle very simple, however the chemical reactions do not readily take place, and unless special materials are used for the electrodes and the electrolyte, the current produced per cm2 is extremely small and the electrical power losses in the electrolyte are very large. To overcome these problems different types of fuel cell have been developed, The different varieties are distinguished by the electrolyte used, though the construction of the electrodes is also different in each case. However, in all types there are separate reactions at the anode and the cathode, and charged ions move through the electrolyte, while electrons move round an external circuit. Another common feature is that the electrodes must be porous, because the gasses must be in contact with the electrode and the electrolyte at the same time.

The types of five types of fuel cell that are in current use, or show that most promise are:-

TYPE	OPERATING TEMP	PRESENT OR POTENTIAL APPLICATIONS
ALKALI	50 - 250 oC	Used in space vehicles (Apollo, Shuttle) Possible uses in land vehicles and submarines
SOLID	50 - 100 oC	Great potential for cars and buses, but also POLYMER a host of other applications
PHOSPHORIC	~220 oC	Medium scale CHP systems. 200kW units in ACID commercial production by IFC Corp., USA
MOLTEN	~600 oC	Medium to large scale CHP systems.1-2 MW CARBONATE trial systems being built now.
SOLID	500 - 1000 oC	All sizes of CHP systems, 2kW to multi MW OXIDE Least developed, but potentially very widely useful

For further details about all these fuel cells, you are referred to an excellent book, "FUEL SYSTEMS EXPLAINED",(2nd edition) by J.Larminie and A.Dicks, published by J.Wiley & Sons, ISBN 0470 84857 X.