Electrochemical direct air capture device squeezes CO2 from the atmosphere

Engineers at the University of Illinois Urbana-Champaign, in collaboration with the Toyota Research Institute of North America, have developed a novel electrochemical device that extracts carbon dioxide directly from ambient air

Published in the journal Environmental Science and Technology, the peer-reviewed study details a battery-like mechanism that relies on electricity and water-based chemistry rather than extreme heat to capture and release legacy carbon emissions.

Targeting the atmospheric “legacy problem”

While traditional carbon-capture technologies are designed for point sources, such as factory smokestacks where CO₂ is heavily concentrated, they do not address the diluted gas already floating in the atmosphere.

“Point source methods are important, but they don’t deal with the vast amount of CO₂ already mixed into the air at much lower concentrations,” said Kyle Smith, professor of mechanical science and engineering at Illinois and the study’s lead investigator. “Our work is aimed at that legacy problem.”

How the electrochemical cell works

Instead of using thermal energy to bind and release carbon, the device functions through a reversible electrochemical process. The architecture centres around specialised potassium-stabilised manganese dioxide electrodes operating inside what the team calls a cation-compensated cell.

The capture and release of CO₂ occurs via a two-step cycle that manipulates the pH levels of a saltwater solution:

• The alkalization phase:

  • The device uses proton-intercalation electrodes to rapidly drive up the alkalinity of the saltwater solution. In this highly alkaline state, CO₂ from the passing air becomes highly soluble, allowing the liquid to eagerly absorb it.

• The purification phase:

  • The cell reverses its electrical operation, decreasing the solution’s alkalinity. This sudden drop in pH forces the absorbed carbon to separate from the liquid and bubble out as a concentrated, purified gas, making it ready for industrial reuse or permanent underground storage.

Redesigning the separation as a thermodynamic cycle

To maximise the system’s energy efficiency, the engineering team mapped the chemical process out as a classical thermodynamic cycle, akin to how engineers optimise traditional power plants. However, instead of tracking standard mechanical variables like pressure and volume, the team plotted the cycle using dissolved inorganic carbon and potassium ion concentrations.

“By framing our process as a thermodynamic cycle in this particular space, we could see where energy was being wasted and how to redesign the cycle,” explained graduate student and co-author JeongA Lee.

Current technical hurdles and scalability

While the early-stage laboratory results are promising, the research team noted that additional engineering adjustments are required before the technology can scale commercially.

The primary efficiency bottleneck involves inter-stream mixing. The device relies on two separate liquid streams, but when the system switches between its capture and release cycles, a small amount of fluid cross-contamination occurs. Graduate student Paul Rozzi noted that limiting or designing around this fluid mixing is the team’s current focus, as resolving it will drastically reduce the device’s overall energy consumption and boost its capture productivity.

The collaborative research holds joint intellectual property, with U.S. patent applications owned by the University of Illinois and co-owned with Toyota as part of the automotive manufacturer’s long-term decarbonization initiatives.