The 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 car.
Either way, you can fill your tank in under three minutes – which is not much different from filling up with petrol. One problem with hydrogen is the bad public relations angle – most of us have heard of hydrogen bombs, and seen the dramatic footage of the hydrogen-filled Hindenberg airship exploding in 1937. But hydrogen can be stored safely – in a series of tests on a tank of liquid hydrogen, BMW played flames at 900oC on it for 70 minutes, punched holes into it, and even squashed it until it broke. Sometimes the hydrogen leaked out, and sometimes it caught alight, but it never exploded. At the moment, in the USA alone, there’s about $200 billion invested in shifting and storing petrol, and it would take an enormous effort to start dealing with hydrogen. It’s a darn shame, but we probably won’t get a hydrogen energy economy in the near future – but we might further down the line, as we begin to run out of fossil fuels.
