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Reverse Combustion: Can CO2 Be Turned Back into Fuel?

Nov 10, 2010 - David Biello - Scientific American

SOLAR FUELS: Using this giant dish made of mirrors, Sandia scientists concentrate sunlight on a specially designed solar-fuel generator that can break down CO2 and water.

Image: Photo by Randy Montoya / Sandia National Laboratories

In the 1990s a graduate student named Lin Chao at Princeton University decided to bubble carbon dioxide into an electrochemical cell. Using cathodes made from the element palladium and a catalyst known as pyridinium—a garden variety organic chemical that is a by-product of oil refining—he discovered that applying an electric current would assemble methanol from the CO2. He published his findings in 1994—and no one cared.

But by 2003, Chao's successor in the Princeton lab of chemist Andrew Bocarsly was deeply interested in finding a solution to the growing problem of the CO2 pollution causing global climate change. Graduate student Emily Barton picked up where he left off and, using an electrochemical cell that employs a semiconducting material used in photovoltaic solar cells for one of its electrodes, succeeded in tapping sunlight to transform CO2 into the basic fuel.

"The dominant thinking 10 years ago was that we should bury the CO2. But if you could efficiently convert it into something that we wouldn't have to spend all that money and energy to put into the ground, sort of recycle it, that would be better," Bocarsly says. "We take CO2, water, sunlight and an appropriate catalyst and generate an alcoholic fuel."

He adds: "We didn't have some brilliant insight here. We had some luck." Luck that venture capitalists are now trying to turn into cash flow via a start-up known as Liquid Light.

Turning CO2 into fuels is exactly what photosynthetic organisms have been doing for billions of years, although their fuels tend to be foods, like sugars. Now humans are trying to store the energy in sunlight by making a liquid fuel from CO2 and hydrogen—a prospect that could recycle CO2 emissions and slow down the rapid buildup of such greenhouse gases in the atmosphere. "You take electricity and combine CO2 with hydrogen to make gasoline," explained Arun Majumdar, director of the Advanced Research Projects Agency–Energy (ARPA–e) that is pursuing such technology, at a conference in March. "This is like killing four birds with one stone"—namely, energy security, climate change, the federal deficit and, potentially, unemployment.

"When these new technologies get commercialized, those jobs always end up in the U.S.," argues chemical engineer Alan Weimer of the University of Colorado at Boulder, who is working on such solar-fuel generators. Adds chemist Michael Berman of the U.S. Air Force Office of Scientific Research, which is funding research into the possibilities of solar fuels, including Bocarsly's work: "The country, and the Air Force, need secure and sustainable sources of energy…. Since the sun provides enough energy for our needs, our goal is to make a fuel using CO2 and sunlight—and maybe water—as feedstocks to produce the chemical fuel that can store the sun's energy in a form that we can use where and when we need.