The second way to use hydrogen to run your car is in an electric car. Mercedes-Benz have been using a strange device called a fuel cell, which has been around since 1839. A fuel cell is very similar to a battery. Both a fuel cell and a battery turn a chemical reaction into electrical energy. A fuel cell is like a battery, but with one important different difference - you can pump in the chemicals indefinitely.
Fuel cells take in hydrogen and oxygen, and give off pure drinking water, and electricity.
You use the electricity to run electric motors. They will get two or three times more energy out of hydrogen, than will a modified car engine. This is because the internal combustion engine has a stage where you generate a lot of heat - and this is where a lot of energy is wasted, and where the efficiency goes right down. The real problem with today's electric cars is that our battery technology is pathetic. The battery pack in today's best electric car, the EV-1, gives great acceleration, but a range of less than 100 kilometres.