UK chemists seek hydrogen store

UK scientists think they have taken a major step forward in making hydrogen a practical replacement for petrol.

Hydrogen has zero greenhouse emissions when "burned" in the novel car engines now under development - but being a gas it is expensive to compress or liquefy.

Now, Newcastle and Liverpool University teams have shown how to store large quantities in super-porous materials based on carbon and nickel.

They describe their work in the journal Science.

The teams say it is proof of concept research which requires many more years of active study. But their approach adds yet another possible solution to the hydrogen storage problem.

'Window' shut

Whilst hydrogen's energy content on a mass-for-mass basis is better than petrol, it has difficulty competing with fossil fuels because it is a gas.

Professor Thomas says new ways to store hydrogen will be developed

An uncompressed hydrogen gas fuel tank that contained a store of energy equivalent to a petrol tank would be more than 3,000 times bigger than its conventional cousin.

Scientists are now trying to get around this. The options include metal alloys that can be persuaded to absorb up to 1,000 times their own volume of hydrogen; and miniscule cylinders of carbon atoms, known as nanotubes, that are more efficient still.

But both of these solutions have their drawbacks, and now the teams from Newcastle and Liverpool Universities have come forward with another approach.

They have investigated a number of synthetic materials including a blue solid containing carbon, nickel, nitrogen and a little oxygen which together form a crystalline "tongue and groove" structure.

Within this lattice there are tiny gaps that are millionths of a millimetre in size where the hydrogen can sit. What is more, these pores are protected by "windows" that "close" once the hydrogen is inside.

Better performance

Professor Matt Rosseinsky, of Liverpool's department of chemistry, said: "Our new porous materials can capture hydrogen gas within their channels, like a molecular cat-flap.

"After allowing the hydrogen molecule - the 'cat' - in, the structure closes shut behind it. The important point is that the hydrogen is loaded into the materials at high pressure but stored in them at a much lower pressure - a unique behaviour."

This is obviously safer if the material is going to form the basis of a fuel tank in a vehicle that could be involved in a shunt.

"The significant design idea here is that the hydrogen doesn't come out easily; you release it by a change in temperature," Professor Mark Thomas, of Newcastle's Northern Carbon Research Laboratories, told BBC News.

The researchers now have to develop their new material ideas further, improving performance and reducing costs.

If and when its storage difficulties are overcome, hydrogen is likely to be used in fuel cells, which convert the chemical energy contained in the gas into electrical energy that can drive a car.

The major motor manufacturers already have this technology built into test and concept vehicles.

"Now that we have a mechanism that works, we can go on to design better ways to store hydrogen which may also be useful in industry," Professor Thomas said.