Artificial leaf energy: how would it work?

Alok Jha
guardian.co.uk, Tuesday 11 August 2009 17.34 BST

An artificial leaf would use a reaction that forms part of the natural process of photosynthesis to turn sunlight and water into a clean fuel source. When light falls on to a leaf, the energy is absorbed and used to carry out specific chemical reactions, helped along by enzymes. The first of these involves splitting water into hydrogen and oxygen, a notoriously difficult thing to do because water molecules are so stable. Plants evolved the ability to do this more than 2.5bn years ago and the reaction is the source of almost all the oxygen in the atmosphere.
The hydrogen created in the water-splitting reaction is then combined in a leaf with CO2 from the atmosphere to make sugars, cell walls and other organic matter. In the artificial version, scientists will use the hydrogen in fuel cells to make electricity or else combine it with CO2 to make fuels such as methanol. This could be used in car engines much as ethanol biofuels are used today and would provide a carbon-neutral source of power.
To make an artificial leaf, scientists are developing artificial analogies of the enzyme, called photosystem 2, used in plants to split water.