A fuel cell combines hydrogen and oxygen into water and in the process creates electricity that is used to power the car. There are several types of fuel cell, but the one used in cars is known as the proton exchange membrane fuel cell (PEM). This is a piece of treated plastic (known as a membrane) sandwiched between two carbon plates.
Pressurised hydrogen gas enters the fuel cell on one side of the membrane and oxygen enters on the other. A chemical catalyst (usually platinum powder) splits the hydrogen into positively charged ions and negatively charged electrons. On the other side, oxygen is split by the catalyst into two negatively charged atoms.
The negative charge of the oxygen attracts the positively charged hydrogen ions through the membrane. However, the membrane does not allow the hydrogen’s two electrons through so they must make their way through an external circuit to the oxygen side, where they join up with the two hydrogen ions and the oxygen to form water.
It is while going through this external circuit that the electrons cause a flow of electricity. This reaction in a single fuel cell produces about 0.7 volts. To increase voltage to a level where it is capable of powering a car many separate fuel cells must be combined to form a fuel-cell stack.
Although it is clean and efficient there are problems with the fuel cell, most importantly that of storing and producing the hydrogen. To be truly green, the original hydrogen used as fuel should have been produced using environmentally friendly methods such as solar or wind power.
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Although many car manufacturers are experimenting with the technology, dates for serious production of fuel cell vehicles vary from 2010 to 2020.