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So you want to run a car on Hydrogen?

We're all carrying around 6Kg (about a stone) of pure hydrogen. So, it would seem that using hydrogen as a fuel is a pretty good bet?

Well, yes and no. On the 'yes' side, we know that hydrogen is the most abundant element in the universe. In fact, the universe is about three quarters hydrogen. It’s even the third most common element in the human body at about 10 per cent. Second is carbon at about 18 per cent, and oxygen comes in first at 65 per cent.

Hydrogen in the universe and human body

If there’s so much hydrogen around, isn’t it the perfect solution?

It's true, pure hydrogen is an excellent fuel. It burns really well and will work in standard petrol engines with only a few minor modifications. It will produce enough power to even keep Jeremy Clarkson happy and the exhaust product is pure water. You could drink it fresh from the exhaust pipe! So even the greenies should be happy, right? Well no actually there are a few problems.

Drinking out of an exhaust pipe

Would Jeremy be impressed?

This is where we get to the 'no' side of things. Hydrogen is a gas and gasses take up much more space than liquids. At normal pressures and temperatures, we could store about 0.45g of hydrogen fuel in a regular five litre fuel tank, like in a Ford Focus. This is enough to give the vehicle a range of about 30 metres. So Jeremy would not be very impressed, affording few opportunities for power sliding.

What we need to do is squash a lot more fuel into the tank. You can do this by turning the hydrogen gas into a liquid. If we do this, our 55 litres of liquid hydrogen will now take Jeremy about 900Km (600 miles). Wow!

Just turn the gas into a liquid!

This is the problem; hydrogen really likes being a gas. It doesn’t turn into a liquid until you cool it down to -252.27°C (-422.086°F). This requires a very big fridge and a lot of energy. It’s much harder to make something cold than to make it hot. It also needs a tank that can withstand very high pressures. With modern composite materials it is in fact possible to make fairly light tanks that will store liquid hydrogen successfully, but they don’t come cheap.

Where can we get the hydrogen?

OK, so we can freeze it and store it in a tank. We said there is loads of it about, but where? This is a very good question. You’ve probably made hydrogen in the school lab using a piece of metal, usually magnesium and an acid. The fizzing produces hydrogen gas that makes that squeaky pop when burned in a test tube. The problem would be making the pure metals and the acids in vast amounts. Huge amounts of energy would be needed and massive chemical factories. Again, this is not even slightly practical.

So where is hydrogen produced?

There are two ways hydrogen is actually produced in large amounts. The first uses natural gas which is methane (CH4) and water (H20). These are heated to about 900°C (1652°F) and passed over a metal catalyst.

This is the reaction:

CH4 + H20 = CO + 3H2

Bingo, pure hydrogen, and some carbon monoxide. It is called steam methane reforming (STR) and over 100 million tonnes of hydrogen is made this way worldwide every year. It is however, very heavy on energy consumption and it would still be much cheaper and greener to burn petrol in your tank. Also, compare this to the worlds total oil consumption of 3,800 million tonnes per year. We would need a lot of methane gas!

The other way is to use electrolysis. Water is H2O. So, if we pass an electric current though it, it splits into hydrogen and oxygen. A really simple process with no nasty waste products.

Hydrogen Reaction

So, is electrolysis the way forward?

Well, can you see a problem here? How do we make the electricity in the first place? At the moment we burn fossil fuels. So we just shift the pollution production from the car engine to the power station. We will have gained – nothing, in pollution or energy terms.

Power stations and electrolysis

This may not be such a problem if nuclear power or renewable energy sources become more common. If nuclear power was cheap, clean and plentiful even Jezza might be driving a mean green Hydrogen machine!

Project

How much hydrogen can you make in the school lab. You will need the help of a friendly (**#@*!) teacher to help you. Could you make enough hydrogen to fill a party balloon? How are you going to prove it is hydrogen!!!

If you succeed in producing enough to fill a very large balloon you may need to ignite it outside! If you light it use a lit splint on the end of a metre rule, and stand back, it really can go off with quite a thump! Send us some pictures of the gear you used to make it and explain how you did it!

The big questions:

Is hydrogen a practical fuel for large scale use at the moment?

Could it ever be made cheaply and in large amounts?

Would it be possible to one day replace petrol stations with hydrogen stations?

Would it be safe or practical to transport large amounts of hydrogen around?