Jun 19 2017
A majority of cars and trucks in the U.S operate on a blend of 90% gasoline and 10% ethanol, a renewable fuel made chiefly from fermented corn. But manufacturing the 14 billion gallons of ethanol consumed yearly by American drivers entails millions of acres of farmland.
Associate Professor Thomas Jaramillo (left) and SLAC Scientist Christopher Hahn have demonstrated the feasibility of designing copper catalysts that convert carbon dioxide into ethanol without corn or other crops. (Image credit: Mark Shwartz/Stanford University)
Stanford University Researchers have recently made a discovery which could lead to a new, more sustainable method to create ethanol without corn or other crops. This technology has three standard components: carbon dioxide, water and electricity supplied through a copper catalyst. The research findings have been published in Proceedings of the National Academy of Sciences.
One of our long-range goals is to produce renewable ethanol in a way that doesn’t impact the global food supply. Copper is one of the few catalysts that can produce ethanol at room temperature. 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.
Thomas Jaramillo, Study Principal Investigator, An Associate Professor of Chemical Engineering at Stanford and of Photon Science at the SLAC National Accelerator Laboratory
Researchers would like to build copper catalysts that selectively convert carbon dioxide into higher-value chemicals and fuels, like propanol and ethanol, with few or no byproducts. But first they require a strong understanding of how these catalysts really work. That is where the recent findings will be able to assist.
Copper crystals
For the PNAS research, the Stanford team selected three samples of crystalline copper, known as copper (111), copper (100), and copper (751). Researchers use these numbers to define 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. The essence of our work is to understand how these different facets of copper affect electrocatalytic performance.
Christopher Hahn, An Associate Staff Scientist, SLAC and the Study’s Co-lead Author
In earlier studies, Researchers had developed single-crystal copper electrodes just one-square millimeter in size. For this research, Hahn and his Co-workers at SLAC came up with a novel way to grow single crystal-like copper on top of large wafers of sapphire and silicon. This method resulted in films of each form of copper with a six-square centimeter surface, 600 times larger than typical single crystals.
Catalytic performance
To compare electrocatalytic performance, the team placed the three large electrodes in water, exposed them to carbon dioxide gas and applied a potential to create an electric current.
The results were perfect. When the team applied a specific voltage, the electrodes made of copper (751) were a lot more selective to liquid products, such as propanol and ethanol, compared to those made of copper (111) or (100).
Eventually, the Stanford team hopes to develop a technology equipped to selectively produce 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. We plan to use this method on nickel and other metals to further understand the chemistry at the surface. We think this study is an important piece of the puzzle and will open up whole new avenues of research for the community.
Thomas Jaramillo, Study Principal Investigator, An Associate Professor of Chemical Engineering at Stanford and of Photon Science at the SLAC National Accelerator Laboratory
Jaramillo also serves as Deputy Director of the SUNCAT Center for Interface Science and Catalysis, a partnership of the Stanford School of Engineering and SLAC. Research Authors include Co-lead Author Toru Hatsukade, Drew Higgins and Stephanie Nitopi at Stanford; Youn-Geun Kim at SLAC; and Jack Baricuatro and Manuel Soriaga at the California Institute of Technology.
The research was funded by the U.S. Department of Energy and the Stanford Global Climate and Energy Project.