August 01, 2013

Artificial photosynthesis to make plants green with envy

JCAP is developing an artificial photosynthesis system that could produce energy-packed liquid fuel using only sunlight, water and carbon dioxide as ingredients.

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Natural photosynthesis—the remarkable ability of plants to transform sunlight into useful energy­—powers virtually all life on Earth. But that’s not enough for some people.

Caltech chemistry professor Nate Lewis and his colleagues aim to show Mother Nature how it really should be done. Their goal is to produce fuel as energy-dense as gasoline and as friendly to the environment as a daffodil.

“Plants are the wrong color to be optimum energy-conversion machines,” Lewis said. “They should be black like solar cells, not green.” He also points out that plants max out their energy conversion at only 10 percent of the light intensity available on a bright, sunny day. The remaining 90 percent of the solar energy they receive goes unused.

Nature presumably has good reasons for wasting so much sunlight. After all, a plant only has to harness enough energy to run its own metabolism, not to satisfy the needs of an energy-hungry civilization. But the Joint Center for Artificial Photosynthesis (JCAP), of which Lewis is scientific director, has more ambitious goals. According to Lewis, artificial photosynthesis will compare to what plants do in much the same way that artificial flight compares to what birds do. We take our inspiration from nature and then strive to surpass it.

JCAP, a U.S. Department of Energy “Energy Innovation Hub,” is America’s largest research program dedicated to turning sunshine into fuel. The artificial photosynthesis system it is developing promises to produce energy-packed liquid fuel at 10 times the efficiency of plants, using only sunlight, water and carbon dioxide as ingredients.

Unlike fossil fuels, JCAP’s product will not contribute to the climate-changing greenhouse effect. And unlike some biofuels, such as those derived from corn, it will not compete with food crops for farmland, require fertilizer or consume large amounts of water. Just set it up in the sunshine and watch the fuel drip out.