BERKELEY, Calif. — Think, for a moment, of carbon dioxide as garbage, a waste product from burning fossil fuels. Like other garbage, almost all of that CO2 is thrown away — into the atmosphere, where it contributes to climate change. A small amount is captured and stored underground to keep it out of the air.
But increasingly, scientists are asking, rather than throwing away or storing CO2, how about recycling some of it?
At laboratories around the world, researchers are working on ways to do just that. The X Prize Foundation has created an incentive, a $20 million prize for teams that by 2020 come up with technologies to turn CO2 captured from smokestacks of coal- or gas-fired power plants into useful products.
But perhaps the ultimate goal of researchers in this field is to turn the waste product of fuel-burning into new fuel. In theory, if this could be done on a large scale using renewable energy or even sunlight, there would be no net gain of emissions — the same carbon dioxide molecules would be emitted, captured, made into new fuels and emitted again, over and over.
“The grand prize is figuring out how to make CO2 be recyclable, a renewable resource,” said Harry A. Atwater, a materials scientist at the California Institute of Technology and director of the Joint Center for Artificial Photosynthesis, which has laboratories at the Lawrence Berkeley National Laboratory here and at Caltech. “That would be a millennial advance for society.”
Carbon dioxide is used to make some basic products like urea fertilizer and specialty plastics. But the processes are not necessarily energy efficient, and almost all use CO2 from natural underground reservoirs. Even if companies started using carbon dioxide that was captured, the amount would be less than 0.5 percent of the roughly 32 billion metric tons of CO2 emitted annually by human activity.
What Dr. Atwater and others have in mind are devices that, if scaled up, could recycle a significant portion of carbon dioxide that is captured from power plants or processes like cement manufacturing, or even directly from the atmosphere.
But developing devices that can efficiently and economically convert large amounts of CO2 will require overcoming many hurdles, not the least of which is all the energy required to split carbon dioxide molecules.
“The big challenge is, how do we go from milligrams to megatons?” said Dick T. Co, a Northwestern University professor and managing director of the Solar Fuels Institute, a group that encourages collaboration among researchers in the field. “How do we make a dent in our energy portfolio when people are working in test tubes today?”
In a research building at the Lawrence Berkeley lab, with a view of San Francisco Bay in the distance, Dr. Atwater leads a team of scientists that is trying to mimic what plants do through photosynthesis. They want to take CO2 and water and, using only sunlight, turn it into fuel.
The center, started in 2010 with a grant from the Department of Energy, devoted its first five years to one aspect of photosynthesis: splitting water into its components, hydrogen and oxygen.
Dr. Atwater, Frances A. Houle, a deputy director, and Karl Walczak, a project scientist, showed some of the fruits of that work — a chip-size sandwich of semiconductor material, catalysts and membranes encased in a clear container with a water-based solution. When the chip was exposed to light, bubbles of gas — hydrogen on one side, oxygen on the other — formed, broke off and rose to the top.
By their calculations, the chip is about 10 times more efficient than a typical plant, which uses about 1 percent of the sunlight that strikes it.
The center is now working on the carbon-dioxide part of the photosynthetic equation. The goal is to integrate the two processes in a device that might look a lot like a solar panel. But rather than generating electricity, it would produce fuel — perhaps methanol, which could be burned directly or converted to gasoline.Read more...
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