Scientists from Cornell University have revisited a century-old electrochemical equation, the Cottrell equation, to aid in the conversion of atmospheric carbon dioxide into a functional product, and in managing this greenhouse gas.
This equation, which bears the name of chemist Frederick Gardner Cottrell who devised it in 1903, now serves as a valuable tool for modern-day researchers. By applying electrochemistry in a controlled lab environment, scientists can gain a clearer comprehension of the diverse reactions that carbon dioxide can undergo.
The electrochemical reduction of carbon dioxide presents an opportunity to transform the gas from an environmental liability to a feedstock for chemical products or as a medium to store renewable electricity in the form of chemical bonds, as nature does.
Their work was published in the journal ACS Catalysis.
The Cottrell equation is a fundamental equation in electrochemistry that describes how the current associated with the reduction or oxidation of a redox species decreases with time during chronoamperometry, a technique where the potential between a working electrode and a reference electrode is abruptly changed and the resulting current is measured over time. Named after Frederick Gardner Cottrell, it states that the current is inversely proportional to the square root of time, provided that diffusion is the only operative mode of mass transport.
“For carbon dioxide, the better we understand the reaction pathways, the better we can control the reaction – which is what we want in the long term,” said lead author Rileigh Casebolt DiDomenico, a chemical engineering doctoral student at Cornell under the supervision of Prof. Tobias Hanrath.
“If we have better control over the reaction, then we can make what we want, when we want to make it,” DiDomenico said. “The Cottrell equation is the tool that helps us to get there.”
The equation enables a researcher to identify and control experimental parameters to take carbon dioxide and convert it into useful carbon products like ethylene, ethane, or ethanol.
Many researchers today use advanced computational methods to provide a detailed atomistic picture of processes at the catalyst surface, but these methods often involve several nuanced assumptions, which complicate direct comparison to experiments, said senior author Tobias Hanrath.
“The magnificence of this old equation is that there are very few assumptions,” Hanrath said. “If you put in experimental data, you get a better sense of truth. It’s an old classic. That’s the part that I thought was beautiful.”
DiDomenico said: “Because it is older, the Cottrell equation has been a forgotten technique. It’s classic electrochemistry. Just bringing it back to the forefront of people’s minds has been cool. And I think this equation will help other electrochemists to study their own systems.”
Reference: “Mechanistic Insights into the Formation of CO and C2 Products in Electrochemical CO2 Reduction─The Role of Sequential Charge Transfer and Chemical Reactions” by Rileigh Casebolt DiDomenico, Kelsey Levine, Laila Reimanis, Héctor D. Abruña and Tobias Hanrath, 27 March 2023, ACS Catalysis.
The study was funded by the National Science Foundation, a Cornell Energy Systems Institute-Corning Graduate Fellowship and the Cornell Engineering Learning Initiative.