Greener Carbon Capture

What if the chemical that makes your jeans bluer could help make carbon capture greener?

Over the past few years, Yayuan Liu, an assistant professor in the Department of Chemical and Biomolecular Engineering, has been experimenting with a library of organic molecules in the hopes of identifying an effective and affordable material for carbon capture technology. Rather than relying on traditional carbon-capture equipment that runs on fossil fuels, she envisioned a new technology that could instead utilize chemicals' natural properties to offset carbon emissions.

Indigo stood out for all the same reasons it's ideal as an industrial dye: It's inexpensive, readily available, and nontoxic. Moreover, it possesses an essential quality that makes it an ideal candidate for greener carbon capture. "If you give an indigo molecule an electron, it will show a strong affinity toward carbon dioxide. You sort of activate that molecule toward carbon capture," Liu explains. "When you take the electron away from indigo, it will release the CO2, which can then be collected and stored underground or used to make polymers, fuel, or other chemicals." In other words, indigo acts sort of like a CO2 magnet that can be turned off and on.

Liu designed a prototype to test whether indigo would bind to carbon dioxide when electricity was added to the system—and it worked. It's just one of the advances Liu has made in the burgeoning field of electrochemically mediated carbon capture since arriving at Johns Hopkins in 2022.

In recent years, carbon capture—the process of trapping carbon dioxide produced by burning fossil fuels and placing it in long-term storage where it cannot negatively impact the atmosphere—has emerged as a promising strategy to combat climate change. But current carbon capture technologies come with a lot of baggage. For one thing, they're incredibly expensive to deploy; for another, figuring out where to store all that carbon, and how to get it there, will be a politically and environmentally fraught process. But the problem Liu is most concerned with is the strategy's continued reliance on the fossil fuels it was designed to mitigate.

Most carbon capture systems use chemicals to separate CO2 from flue gas, the white clouds that billow from the smokestacks of power plants. The captured carbon dioxide is then compressed and shipped for storage or reuse. All of this requires a significant amount of energy: to pump the flue gas to different parts of the plant, to cool and compress the CO2, to "recharge" the chemicals used in the process. Currently, natural gas plants that employ carbon capture technologies use about 15% of the energy they produce to power that equipment. Coal plants use as much as a quarter of their energy output to run carbon capture equipment.

Because of these challenges, Liu says, the development and deployment of carbon capture technology is moving at a worryingly slow pace. "I saw an opportunity to develop carbon capture using renewable energy."

Liu's work landed her on the 2023 MIT Technology Review's 35 Innovators Under 35 list, a prestigious award that's been given to tech luminaries like Meta co-founder Mark Zuckerberg and CRISPR pioneer Feng Zhang. That same year she was awarded a National Science Foundation Early CAREER Award, which funded work she undertook to make indigo an even more robust option for cleaner carbon capture.

"One of the biggest challenges in using these materials [such as indigo] is that they are also very sensitive to oxygen. Oxygen would compete with CO2 for binding, and therefore the existence of oxygen would compromise the efficiency," Liu says. She and her fellow researchers recently published a paper in Nature Communications introducing the novel use of chemical reactions to stabilize indigo molecules against oxygen, "potentially solving the sensitivity issue."

The next step, Liu says, is getting this technology out of the lab and into the real world, "in realistic conditions using real gas and real air."

While Liu has designed and tested the new technology largely to help commercial factories, she is thinking on a more granular level, too. Because of their reliance on fossil fuel–generated heat, traditional carbon capture systems are more efficient when deployed at large scales, but Liu's renewable energy–powered systems could be efficient at much smaller scales, too. "In the future, maybe every household will have a carbon capture device so they can capture the CO2 they create."

Whether her work leads to viable ways to remove carbon dioxide from a factory smokestack or a clothes dryer vent, Liu feels confident "we can achieve something scalable and practical in the next five to 10 years." It's an exciting prospect, but time is of the essence. "Given the urgency of this issue," she says, "we need to act even faster."