SAN FRANCISCO, July 8 (Xinhua) -- A recent discovery by a team of Stanford University researchers could lead to a new, more sustainable way to make ethanol without corn or other crops.
The technology has three basic components, namely water, carbon dioxide and electricity delivered through a copper catalyst.
It is expected to address the status quo that most cars and trucks in the United States run on a blend of 90 percent gasoline and 10 percent ethanol, a renewable fuel made primarily from fermented corn and that producing the 14 billion gallons, or nearly 53 billion liters, of ethanol consumed annually by American drivers requires millions of acres of farmland.
"One of our long-range goals is to produce renewable ethanol in a way that doesn't impact the global food supply," said Thomas Jaramillo, an associate professor of chemical engineering at Stanford and of photon science at the SLAC National Accelerator Laboratory and principal investigator of the study published in Proceedings of the National Academy of Sciences.
"Copper is one of the few catalysts that can produce ethanol at room temperature," Jaramillo noted. "You just feed it electricity, water and carbon dioxide, and it makes ethanol. The problem is that it also makes 15 other compounds simultaneously, including lower-value products like methane and carbon monoxide. Separating those products would be an expensive process and require a lot of energy."
Therefore, the goal is to design copper catalysts that selectively convert carbon dioxide into higher-value chemicals and fuels, like ethanol and propanol, with few or no byproducts.
For the study, the Stanford researchers chose three samples of crystalline copper, known as copper (100), copper (111) and copper (751). They use these numbers to describe the surface geometries of single crystals.
"Copper (100), (111) and (751) look virtually identical but have major differences in the way their atoms are arranged on the surface," Christopher Hahn, an associate staff scientist at SLAC and co-lead lead author of the study, said in a news release.
"The essence of our work is to understand how these different facets of copper affect electrocatalytic performance."
Researchers in previous studies created single-crystal copper electrodes just 1-square millimeter in size.
In the new research, Hahn and his co-workers at SLAC developed a novel way to grow single crystal-like copper on top of large wafers of silicon and sapphire. This approach resulted in films of each form of copper with a 6-square centimeter surface, 600 times bigger than typical single crystals.
To compare electrocatalytic performance, they placed the three large electrodes in water, exposed them to carbon dioxide gas and applied a potential to generate an electric current.
The results were clear. When the team applied a specific voltage, the electrodes made of copper (751) were far more selective to liquid products, such as ethanol and propanol, than those made of copper (100) or (111).
Ultimately, the Stanford team would like to develop a technology capable of selectively producing carbon-neutral fuels and chemicals at an industrial scale.
"The eye on the prize is to create better catalysts that have game-changing potential by taking carbon dioxide as a feedstock and converting it into much more valuable products using renewable electricity or sunlight directly," Jaramillo said.