Because the Earth’s atmospheric carbon dioxide (CO2) levels are dangerously high (now more than 400 parts per million), a recently discovered process that converts CO2 into useable ethanol is a very big deal. The US alone currently uses billions of gallons of ethanol for fuel each year. It’s also exciting because it was a surprising discovery. The ethanol was produced with a nanotechnology-based catalyst that scientists at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) expected would likely produce methanol. ORNL in Tennessee is the Department of Energy’s largest science and energy lab.
ORNL explains that the catalyst’s “novelty lies in its nanoscale structure, consisting of copper nanoparticles embedded in carbon spikes.” Adam Justin Rondinone, Ph.D., is the lead author of this study in Chemistry Select, titled “High-Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle/N-Doped Graphene Electrode.” Senior Staff Scientist Rondinone is the leader of Helium-ion microscopy and chemical imaging research at the Center for Nanophase Materials Sciences and the outreach coordinator for the Center for Nanophase Materials Sciences. He offered us some helpful insights into the research.
“We had been studying the carbon nanospikes, without copper nanoparticles, for a few years before this discovery. Our center has studied carbon catalysts for years, because they are low-cost, don't require rare metals, and can be tuned. “
When low voltage is applied to this catalyst, it triggers a complex electrochemical reaction. Rondinone explained that while studying the first step of the proposed reaction, the scientists realized that the catalyst was “doing the entire reaction on its own.” The result is that a solution of CO2 dissolved in water turned into ethanol with a yield of 63 percent. Here’s Rondinone’s insight into the original expected outcome for the catalyst:
“Scientists have studied electrochemical conversion (technically it's called 'reduction') of carbon dioxide to other products for quite a while--since the 1980’s or even a bit before. Based on literature reports for nanocrystalline copper, we expected methane or methanol, which is a product that doesn't need a bond to be formed between two carbon atoms. That is, it's the simplest product. In order to get ethanol in high yield, we needed to have a carbon-carbon bond formed for most of the carbon dioxide to go through the reaction. That outcome was unexpected because it's much more difficult to do. We are still a bit unsure why C2 products are the highest yield. We believe we know the answer but haven't yet proven it.”
I asked Rondinone to share how he felt when he realized this process was reversing combustion and creating ethanol from CO2 with unexpected efficiency:
“Truthfully, it's initially a mixture of elation and skepticism. The first response is, 'do it again.' Once we realized it was repeatable, then we knew we had a very interesting finding on our hands.”
Because this catalyst uses less expensive materials and operates in room-temperature water, it is easy to turn on and off, economically viable, and could likely be scaled to industry proportions.
ORNL also shares that "...the process could be used to store excess electricity generated from variable power sources such as wind and solar...A process like this would allow you to consume extra electricity when it’s available to make and store as ethanol. This could help to balance a grid supplied by intermittent renewable sources.” Here’s more information from Rondinone on that possibility:
“We believe this to be true--that this catalyst (or one like it) could be used to convert wind power to a liquid fuel. Wind power is unreliable due to constantly changing weather conditions. Using large amounts of wind power to supply the grid is not currently possible. We are limited to around 20% wind, with the rest supplied by more reliable sources such as natural gas, nuclear, and coal. Finding a better use for wind power could allow us to use more of it, or to at least use what we have more efficiently. This catalyst will tolerate variability in ways that the grid cannot, so it could be run entirely on wind.”
Here are the team’s next steps:
“The next steps are to diversify our efforts. We will continue to investigate the basic science of the catalyst, but we also intend to quickly answer some of the scaling and economic questions that we have heard. There is no known physical reason why this catalyst cannot be scaled, but we must do it to ensure that is true. We must also measure lifetime and potential poisoning effects to begin to understand which types of CO2 sources might be appropriate. An economic model will help us to understand if the catalyst will be competitive with other ethanol sources, such as corn.”
This conversion of CO2 into fuel is an exciting breakthrough in the study of waste-to-fuel technology and reverse combustion. As Avery Thompson of Popular Mechanics puts it, this “process is cheap, efficient, and scalable, meaning it could soon be used to remove large amounts of CO2 from the atmosphere.” It is also an important step in reducing our dependence on the limited fossil fuels in the ground.
The study’s co-authors are: Yang Song, Rui Peng, Dale Hensley, Peter Bonnesen, Liangbo Liang, Zili Wu, Harry Meyer III, Miaofang Chi, Cheng Ma, Bobby Sumpter, and Adam Rondinone.