Electric Approaches Reshape Carbon Capture Tech

A quiet shift is happening in the carbon capture sector. For years, most machines that pull carbon dioxide out of ambient air, known as direct air capture (DAC) systems, have relied on steam for heat. Heating is a critical step for freeing and collecting the CO2 after it’s captured. But using steam for this is inefficient, and lately several companies have been experimenting with novel electrical approaches.

One company, AirCapture in Berkeley, Calif., uses microwaves to generate heat, and in June won a Tencent CarbonX 2.0 award for it. Another, the startup Sustaera, in Durham, N.C.,, uses resistive heating in its lab-scale machine, and in March announced it had reached an efficiency that’s more than three times higher than steam. And London-based Mission Zero Technologies built a membrane electrodialysis machine that bypasses the need for heat altogether.

The efforts follow a tumultuous batch of years for commercial DAC technologies. Companies in this sector aim to remove gobs of CO2 from the atmosphere to slow global warming and sell the credits on carbon markets. But they’re plagued by high costs, inefficiencies, commercial setbacks, struggling carbon markets and, in the United States, political headwinds. So far, they haven’t made a dent in removing the greenhouse gas.

DAC “is something we all need to have, but no one wants to pay for, so we need to make it as low-cost as possible,” says Cory Sanderson, CEO and co-founder at Sustaera. “People are pivoting into [electrical approaches] because steam is not going to work, and I think the industry is finally realizing that.”

Steam vs. Electric DAC Efficiency

In a typical steam-based DAC system, big fans draw in ambient air and run it over a bed of sorbent material housed in collector units. The sorbent soaks up CO2 and when it’s saturated, the collector units close. Then, steam fills the chambers, heating the sorbent and breaking its chemical bonds with CO2, freeing it for collection—a step called desorption. Zurich-based Climeworks–one of the biggest names in atmospheric carbon capture–does it this way.

“People are using steam because it’s a very mature industrial practice,” says Zeyan Liu, an electrochemist at Northwestern University in Evanston, Illinois. But “we see there’s a trend moving from steam to electricity,” he says.

That’s because there’s a limit on how efficient steam-based desorption can be. For one, steam fills its containment space, heating up not just the sorbent but everything it touches. Steam also must undergo phase changes–from vapor to liquid and back–and the efficiency of that is limited by thermodynamics. Plus, steam struggles in cold environments.

Electric heating approaches can be more targeted. They heat only the sorbent—or even just the chemical bonds within the sorbent—without heating the rest of the collector unit. That’s why Sustaera chose resistive heating, also known as Joule heating.

In this approach, an electric…