carbon dioxide that much It is a greenhouse gas that is solely responsible for 78% of the change in the Earth's atmospheric energy balance from 1990 to 2022.
Carbon dioxide, a byproduct of fossil fuel combustion, enters the atmosphere from automobile exhaust and coal-fired power plants. Some renewable energy sources also produce small amounts of carbon dioxide, but only a fraction of the amount produced by coal and natural gas.
At its core, the molecule is just an arrangement of one carbon and two oxygen atoms that can be reconstituted into clean fuels and useful chemicals through a process called electrochemical carbon dioxide reduction (CO2R). However, the process is often at a loss due to competing processes that pull atoms in undesirable directions, producing undesirable byproducts.
In a paper published today natural catalystResearchers at the Amanchukwu Lab at the UChicago Pritzker School of Molecular Engineering have described how to manipulate water molecules to make CO2R more efficient, with the ultimate goal of creating a clean energy loop.
The new method allowed the research team to perform CO2R with almost 100% efficiency under mildly acidic conditions using gold or zinc as catalysts.
“Imagine if you could get green electricity from solar and wind and then use that electricity to convert carbon dioxide back into fuel,” said Reggie Gomes, a PME PhD candidate and first author of the new paper.
compete with her
Electrochemically breaking down a molecule is like a break shot in a game of billiards. Previous arrangements disappear and the balls scatter across the table, coming to rest in new combinations that don't always match what the player intended.
Similarly, researchers doing CO2R use electricity and water to break down and rearrange harmful greenhouse gases. This sends the carbon and oxygen atoms from the carbon dioxide caroming across the table along with the hydrogen atoms from the water.
When it works as intended, the atoms form other, more desirable molecules that can be used as fuel or chemicals.
However, as the atoms split apart, a stable pair of two hydrogen atoms is often formed, a process called the hydrogen evolution reaction (HER). This makes CO2R less efficient because the energy and atoms that become hydrogen gas cannot become part of the molecules the scientists were trying to create.
Even in small amounts of water, CO2R always competes with HER.
Amanchukwu's lab, best known for its battery research, applied insights from water-based batteries to the problem and hypothesized that controlling water as an organic solvent might provide a solution.
everything that sparkles
Both CO2R and HER rely on water as a proton donor. Using organic solvents and acidic additives, the team was able to tune the water's behavior to find the sweet spot where it donates the right amount of protons to produce the intended molecules rather than other unwanted substances such as hydrogen gas and carbonates.
“In general chemistry, we learned that carbon dioxide reacts with hydroxide to form carbonate, which is undesirable because it depletes the molecules we want to value,” said Chibueze Amanchukwu, Neubauer Family Assistant Professor of Molecular Engineering.
Many of the most effective ways to do CO2R rely on precious metals.
“Platinum, silver and gold are great catalysts for research purposes,” Gomes said. “They are very stable materials. But if you think about industrial applications, they are expensive.”
By engineering the electrolyte, the new method can achieve similar results using cheaper, more abundant materials.
“Currently, the best way to do this electrochemically at room temperature is to use noble metals. Gold and silver can slightly inhibit the hydrogen evolution reaction,” Amanchukwu said. “With our discovery, we can now use zinc, a metal that is abundant on Earth, because we now have a separate way to control water.”
The American Chemical Society's Chemical & Engineering News recently named Amanchukwu one of its annual 12 talented “young scientists who are making the world a better place through chemistry.”