Artificial leaves created by the Joint Center for Artificial Photosynthesis (JCAP) in Berkeley, Calif., promise to provide a carbon-neutral alternative to fossil fuels. Made from a silicon-based material, the prototype leaves can convert sunlight, carbon dioxide and water into hydrogen fuel, similarly to how plants undergo photosynthesis.

The leaves absorb light, tipping off a series of chemical reactions. Iridium oxide catalysts split water into oxygen and protons, and those protons are separated out by a membrane. Then platinum catalysts convert the protons into hydrogen.

Solar energy is a vast resource that is mostly untapped -- in one hour, the sun projects more energy on the Earth than the entire human population can use in a year. But efficiently capturing and storing energy from the sun is difficult. Biofuels store less than 1 percent of the sun's energy that touches them, and energy from simple solar panels isn't easily stored.

Artificial photosynthesis has the potential to retain a larger amount of the sun's energy in a portable form, which could be used as clean fuel for planes, ships and automobiles.

Funded by a five-year, $122 million grant from the Department of Energy, JCAP envisions a plan to blanket millions of acres of nonarable land with the artificial leaf material. This could completely offset all the energy consumed by U.S. transportation, said Heinz Frei, acting director of the JCAP lab.

But artificial photosynthesis technology is, at this point, extremely costly, and the hydrogen fuel that is currently being produced is inefficient.

"I would not be surprised to learn that one day this will be done on a practical scale, at a reasonable cost," said Sally Benson, director of the Global Climate and Energy Project at Stanford University. "But we are very far from that point" (James Temple, Houston Chronicle/Fuel Fix, Jan. 14). -- EH