The Economist

September 4, 2007

Alternative energy

A new alloy may revive hope for the hydrogen economy

HYDROGEN has long been touted as an environmentally friendly alternative to fossil fuels. Cars that run on the stuff produce only water as waste-though hydrogen's overall benefits depend on how cleanly the gas itself is produced. But efforts to use it more widely have stalled in part because of the difficulty and danger of storing and transporting hydrogen; a certain incident with a dirigible called the Hindenburg lingers in the collective memory.

One way to sidestep these problems would be to create hydrogen at the point of use. Much effort has gone into replicating a feat at which plants excel: splitting water into its constituent hydrogen and oxygen. So far, however, the process has proved tricky and the results have been uninspiring. Now Jerry Woodall and his colleagues at Purdue University, in Indiana, have devised a new approach that takes the form of small pellets of an alloy of two metals, aluminium and gallium.

The alloy's action is remarkably simple. Aluminium is so partial to oxygen that it can rip it out of a water molecule. The result is loose hydrogen, and the oxygen thus freed combines with aluminium to make its oxidised cousin alumina, the form in which the metal is found in nature. The reason this does not happen to kitchen saucepans is that aluminium at the surface will normally pluck oxygen from the air to form a protective skin of oxide that blocks further oxidation. The trick to using aluminium to liberate hydrogen is to prevent this layer from forming.

That is where the gallium comes in. Mixing it with aluminium prevents the formation of the oxide skin so that, in the presence of water, each and every atom of aluminium is available to free up hydrogen. As it does so, it leaves behind alumina powder and liquid gallium, which can both be reused.

Of course, the alumina needs to be converted back into aluminium and combined with the recycled gallium, a process that uses energy. This extra step not only reduces the efficiency of the system but, with today's power stations, would also be a source of greenhouse gases. Even so, Dr Woodall and his colleagues reckon that the carbon dioxide emissions of the cycle work out to about half those of petrol if the hydrogen is used directly in a normal combustion engine; still less if it is used in a fuel cell. And, so long as the alumina can be recovered relatively easily, the cost of running such a vehicle would be similar to using petrol.

The technology has been licensed to an aptly named start-up company called AlGalCo. The first demonstrations of the commercialised process will be in emergency power and small, low-power applications like golf carts. If AlGalCo's products prove as simple and as economical as Dr Woodall's experiments, hydrogen could be back in the race.

posted to ClimateConcern