Stackable artificial leaf for CO2 capture works in the real world

Technology News | January 28, 2022

By Rich Pell

Unlike other carbon capture systems, which work in labs with pure carbon dioxide from pressurized tanks, say the researchers, their artificial leaf works in the real world. It captures carbon dioxide from more diluted sources, like air and flue gas produced by coal-fired power plants, and releases it for use as fuel and other materials.

“Our artificial leaf system can be deployed outside the lab, where it has the potential to play a significant role in reducing greenhouse gases in the atmosphere thanks to its high rate of carbon capture, relatively low cost and moderate energy, even when compared to the best lab-based systems,” says Meenesh Singh, assistant professor of chemical engineering in the UIC College of Engineering and corresponding author on a paper describing the work.

Using a previously reported theoretical concept (see “Moving artificial leaves out of the lab and into the air“) the scientists modified a standard artificial leaf system with inexpensive materials to include a water gradient – a dry side and a wet side – across an electrically charged membrane. On the dry side, an organic solvent attaches to available carbon dioxide to produce a concentration of bicarbonate, or baking soda, on the membrane.

As bicarbonate builds, these negatively charged ions are pulled across the membrane toward a positively charged electrode in a water-based solution on the membrane’s wet side. The liquid solution dissolves the bicarbonate back into carbon dioxide, so it can be released and harnessed for fuel or other uses. The electrical charge is used to speed up the transfer of bicarbonate across the membrane.

The system, which is small enough to fit in a backpack, was tested and found to have a very high flux – a rate of carbon capture compared with the surface area required for the reactions – of 3.3 millimoles per hour per 4 square centimeters. This is more than 100 times better than other systems, even though only a moderate amount of electricity (0.4 KJ/hour) was needed to power the reaction, less than the amount of energy needed for a 1 watt LED lightbulb.

The researchers say they calculated the cost at $145 per ton of carbon dioxide, which is in line with recommendations from the Department of Energy that cost should not exceed around $200 per ton.

“It’s particularly exciting that this real-world application of an electrodialysis-driven artificial leaf had a high flux with a small, modular surface area,” says Singh. “This means that it has the potential to be stackable, the modules can be added or subtracted to more perfectly fit the need and affordably used in homes and classrooms, not just among profitable industrial organizations. A small module of the size of a home humidifier can remove greater than 1 kilogram of CO2 per day, and four industrial electrodialysis stacks can capture greater than 300 kilograms of CO2 per hour from flue gas.”

For more, see “Migration-assisted, moisture gradient process for ultrafast, continuous CO2 capture from dilute sources at ambient conditions.”