Scientists use solar energy to create liquid fuel from greenhouse gas

Posted by Wolfgang Gruener

Chicago (IL) – Carbon dioxide (CO2) emissions dominate today’s environmental discussions: A single large SUV’s are estimated to blow out more than 100 tons of the gas over their life time and contribute to significantly to global warming. While especially car manufacturers look for ways to reduce CO2 emissions in future vehicles, scientists went the other way and claim they have found a way to actually use CO2 as a renewable energy source.

The idea of the approach dates back to the 1920s, when German scientists developed a technology to convert carbon monoxide into liquid fuel. Now chemists at the University of California, San Diego said that they have built and demonstrated a prototype device that can capture energy from the sun, convert it to electrical energy and “split” carbon dioxide into carbon monoxide (CO) and oxygen.

The “device” is still deep into the research phase, as the scientists said they still need additional energy for the process to work. But the approach looks promising and considering today’s fuel prices as well as environmental concerns, the idea is likely to get a lot of attention.  

 

“For every mention of CO2 splitting, there are more than 100 articles on splitting water to produce hydrogen, yet CO2 splitting uses up more of what you want to put a dent into,” said Clifford Kubiak, professor of chemistry and biochemistry UCSD.  “It also produces CO, an important industrial chemical, which is normally produced from natural gas.  So with CO2 splitting you can save fuel, produce a useful chemical and reduce a greenhouse gas.”

According to Kubiak and his graduate student Aaron Sathrum, the process to split carbon dioxide utilizes a semiconductor and two thin layers of catalysts.  It splits carbon dioxide to generate carbon monoxide and oxygen in a three-step process.  First, solar energy photons are captured by the semiconductor; next, optical energy is converted into electrical energy by the chip.  During the third step, electrical energy is provided to the catalysts.  The catalysts then convert carbon dioxide to carbon monoxide on one side of the device and to oxygen on the other side.
 
Kubiak and Sathrum used a silicon semiconductor to test their device because of the broad knowledge of silicon characteristics.  However, they consider silicon as “too wimpy” as it cannot supply enough energy to split carbon dioxide. The team is now building a new device using a gallium-phosphide semiconductor, which is described to have twice the band gap of silicon and absorbs more energetic visible light than silicon can. Kubiak and Sathrum believe that this material will we enable the creation of enough energy to drive the catalytic splitting of carbon dioxide.