Ethanol is one of the most important biofuels used in the world and researchers could soon reduce its impact on the environment significantly.
Thanks to a new technique, ethanol could soon be produced directly from carbon dioxide in the atmosphere. Ethanol is currently made primarily from fermented corn, so it takes a sizable chunk of agricultural resources. The new method, presented in the Proceedings of the National Academy of Sciences, uses water, carbon dioxide, and electricity delivered through a copper catalyst.
"One of our long-range goals is to produce renewable ethanol in a way that doesn't impact the global food supply," principal investigator Thomas Jaramillo, an associate professor of chemical engineering at Stanford and of photon science at the SLAC National Accelerator Laboratory, said in a statement.
The secret to this new method is in the particular crystal structure used for the copper. The team used three types of copper – copper (100), copper (111), and copper (751) – and tested their ability to convert water and carbon dioxide into ethanol.
"Copper (100), (111) and (751) look virtually identical but have major differences in the way their atoms are arranged on the surface," said Christopher Hahn, an associate staff scientist at SLAC and co-lead author of the study. "The essence of our work is to understand how these different facets of copper affect electrocatalytic performance."
The team discovered that a particular arrangement in copper (751), where the atoms are quite far apart and with only two close neighbors, allows for the production of more liquid fuel than other types of copper.
"An atom of copper (751) only has two nearest neighbors," Hahn said. "But an atom that isn't bonded to other atoms is quite unhappy, and that makes it want to bind stronger to incoming reactants like carbon dioxide. We believe this is one of the key factors that lead to better selectivity to higher-value products, like ethanol and propanol."
While biofuels are carbon neutral, they still use resources that could be used for food production. They also have been linked to potential deforestation in developing countries. This method might provide a truly green alternative.
"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 added.
In order to look for the best possible set up, the team aim to test the same approach on other metals to see how different surfaces affect ethanol production.