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<\/a><\/p>\nThe calculation \u2013 named the Cottrell equation for chemist Frederick Gardner Cottrell, who developed it in 1903 \u2013 can help today\u2019s researchers understand the several reactions that carbon dioxide can take when electrochemistry is applied and pulsed on a lab bench.<\/p>\n
Their work was published March 28 in the journal\u00a0ACS Catalysis<\/a>.<\/p>\n \u201cFor carbon dioxide, the better we understand the reaction pathways, the better we can control the reaction \u2013 which is what we want in the long term,\u201d said lead author Rileigh Casebolt DiDomenico, a doctoral student in the Smith School of Chemical and Biochemical Engineering, in Cornell Engineering under the supervision of Prof. Tobias Hanrath.<\/p>\n 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.<\/p>\n \u201cIf we have better control over the reaction, then we can make what we want, when we want to make it,\u201d DiDomenico said. \u201cThe Cottrell equation is the tool that helps us to get there.\u201d<\/p>\n In simple terms, the equation depicts a change in the measured electrochemical current over specific references to time during an experiment. What that means in a lab is that carbon dioxide is subjected to various applied potentials stepped up or down, or pulsed and these, in turn, generate a current that is related to the products formed from the reduction of carbon dioxide.<\/p>\n DiDomenico first encountered this antique equation as a doctoral student in a class taught by\u00a0H\u00e9ctor Abru\u00f1a<\/a>, the Emile M. Chamot Professor of Chemistry and Chemical Biology, in the College of Arts and Sciences, a senior author on the paper.<\/p>\n Intrigued after Abru\u00f1a mentioned it in class, DiDomenico implemented the Cottrell equation in her own work on carbon dioxide reduction. She changed the electrochemical values (such as applied potential) or the time scale, to generate other products derived from the gas.<\/p>\n As an example, 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.<\/p>\n At first, DiDomenico thought she got strange results, but confirmed later that she had conducted the experiments correctly.<\/p>\n \u201cI was trying to change the pulse profile to make ethylene specifically<\/p>\n by applying what I was learning in class to see if it fit,\u201d DiDomenico said. \u201cI realized that this was actually a way that we could identify a mechanism for reducing carbon dioxide into a useful product.\u201d<\/p>\n 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\u00a0Tobias Hanrath<\/a>, the Marjorie L. Hart \u201850 Professor in Engineering, in the Smith School of Chemical and Biomolecular Engineering.<\/p>\n \u201cThe magnificence of this old equation is that there are very few assumptions,\u201d Hanrath said. \u201cIf you put in experimental data, you get a better sense of truth. It\u2019s an old classic. That\u2019s the part that I thought was beautiful.\u201d<\/p>\n Abru\u00f1a enjoyed seeing the equation employed. \u201cThis equation describes what happens when one imposes a potential step, so you go from one voltage to another, and then look at the resulting current transient,\u201d he said. \u201cBy analyzing the results, you can derive interesting and important mechanistic information and details. It\u2019s just that unless you\u2019re an electrochemical nerd like me, you probably don\u2019t know much about that.<\/p>\n \u201cPeople in the business of carbon dioxide reduction are much more into product distributions, or the engineering aspects of that,\u201d Abru\u00f1a said. \u201cHere we are using a very simple model that worked amazingly well. It\u2019s almost embarrassingly good.\u201d<\/p>\n DiDomenico said: \u201cBecause it is older, the Cottrell equation has been a forgotten technique. It\u2019s classic electrochemistry. Just bringing it back to the forefront of people\u2019s minds has been cool. And I think this equation will help other electrochemists to study their own systems.\u201d<\/p>\n