A fuel cell is a type of battery which converts the chemicals hydrogen and oxygen into water, and in the process produces electricity.

Hydrogen is pumped into the cell from an on board tank, while the oxygen is taken from the air outside. Together they form steam, which is emitted through the car's exhaust.

Some car makers are putting a lot of time and effort into developing hybrid cars where the electric motors are powered by fuel cells.

Hydrogen is the most abundant element in the universe, but it is highly flammable; that is, it bursts into flames easily and as the lightest gas, it just floats away. Even so, it can be extracted from water, fossil fuels, and other substances.

The problem is to compress, or squeeze, hydrogen into a tank small enough to fit in a car. The tank can be topped off with hydrogen at refueling stations, but there are very few of such places available at this time.

The advantages and disadvantages of fuel-cell cars

In theory, electric-fuel-cell cars could be the answer for clean cars of the future:

• Fuel cells are reliable and make little noise since they have no moving parts.
• Water is the only thing emitted through the exhaust.

There are a number of challenges still to be overcome:

• Increasing the amount of electricity produced so the car has more power.
• Compressing and safely storing enough hydrogen into a small tank for hundreds of miles of driving.
• Making affordable cars which are now very expensive in that a fuel-cell system costs ten times more to make than a conventional engine.