Hydrogen Car
The trouble with today's cars is that they still put out a lot of pollution, and use up fossil fuels. One day, we have to run out of fossil fuels. People have been talking about running cars on water for ages. Unfortunately, most of the time, these people are crackpots. But there is a certain amount of truth in what
they say.
Now I know that trying to predict the future is hard, but I think that an electric car, powered by a fuel cell running on hydrogen, could be a goer! If you remember back in chemistry classes at school, water is H2O. In other words, a molecule of water is made up of two atoms of hydrogen, and one atom of oxygen. If you use energy, and pass electricity through water, you can split water into hydrogen and oxygen. And you can run this reaction backwards, and combine hydrogen and oxygen to give you water and energy. (In fact, the word, "hydrogen", means "maker of water" in the original Greek
language.)
There are two main ways that you can burn hydrogen with oxygen, to give you water, and energy. The first way is that you can burn hydrogen in a modified car engine. Two
companies, BMW and Mazda, are working on this. The engine works fine, but
with about 20% less power - which is pretty reasonable, considering that we
have been working on the petrol engine for a century or so. When you burn
hydrogen in an engine, you get mostly water coming out of the tailpipe. You
also get small amounts of oxides of nitrogen (from the nitrogen in the air), and
even smaller amount of hydrocarbons (from traces of the lubricants in the
combustion chambers of the engine). Even so, a hydrogen-powered car is
much less polluting than a petrol-powered car. Of course, you use a normal
gearbox and diff.

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. But a battery is sealed, and when the
"goodness" in the chemicals is used up, the battery is flat. 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.

Fuel cells are up to 80% efficient. 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. But if you use a fuel cell
instead of a battery, you suddenly get an electric car with very low pollution,
and good range and performance.

There are two main ways to store hydrogen in your car-of-the-future. First,
you can squash it and turn it into a liquid - but the container has to be very
strong and heavy, and you have to insulate it to keep it at a temperature of
about 260oC below zero.

The second way is to shove the gas into a metal, such as magnesium, and it
will squash into the spaces between the magnesium atoms. It sounds
unbelievable, but you can actually store more hydrogen inside a metal, than
you can as a liquid. Nelly Rodriguez and her fellow scientists at Northeastern
University in Boston claim that they can do even better. They used incredibly
thin sheets of graphite only one third of a billionth of a metre apart, and they
reckon that they can store 30 litres of hydrogen on a single gram of graphite,
which works out to an amazing 8,000 kilometres per tank, with your
hydrogen-powered