Captura employs the oceans to fight climate change

The ocean holds many mysteries. But one thing we do know is that it soaks up almost a third of the carbon dioxide released into the atmosphere. Captura wants to harness this natural carbon-removal prowess to help cool the earth.

Projects to pull CO₂ out of air, known as direct air capture (DAC), are starting to take off around the world. But they typically require large fans that send air over expensive sorbents. “The ocean is already doing this job at a massive scale,” Captura CEO Steve Oldham says.

Captura strips CO₂ out of the ocean, allowing the waters to draw more CO₂ from the atmosphere. “We’re not adding materials or fundamentally changing the way the ocean works,” Oldham says. “We’re utilizing its tremendous size and power to help us.”

Captura’s direct ocean capture (DOC) technology relies on electrodialysis—the transport of ions across membranes using an electric field—which is used today for desalination. It sends a small seawater stream through an electrodialysis reactor, where a series of membranes split the salt and water into their constituents—sodium, chlorine, hydrogen, and oxygen—and rearrange the atoms into hydrochloric acid and sodium hydroxide.

Captura adds the acid to seawater in large tanks. This causes dissolved inorganic carbon in the water to turn into CO₂, which is easy to extract. The company plans to store the extracted CO₂ in geological formations or convert it into fuels and other products. It adds the sodium hydroxide, a base, to the water to restore its alkalinity before returning it to the sea.

The novel membrane at the heart of the process was born in CX Xiang’s laboratory at the California Institute of Technology. His group has been developing the membranes for over a decade to split water and make fuels using solar energy.

Xiang realized that the concept translated seamlessly to drive acid-base generation from seawater. So he and fellow applied physics and materials science professor Harry Atwater pivoted to DOC with early funds from the US Department of Energy’s Advanced Research Projects Agency–Energy (ARPA-E).

Things moved rapidly after Xiang and Atwater, now chief technology officer and chief science officer, respectively, cofounded Captura in 2021. Within a year, they had scored a $1 million award in the XPrize Carbon Removal competition and $500,000 from ARPA-E.

The company brought Oldham on board in April 2022, then began raising funds from venture capitalists. He was formerly CEO of the DAC leader Carbon Engineering, where over 4 years he helped take DAC from an obscure, eyebrow-raising concept to a commercial endeavor. Occidental Petroleum acquired Carbon Engineering last year for $1.1 billion.

Oldham’s ability to explain DOC’s viability was crucial, Xiang says. “When we talked to investors, the first question was usually, ‘Wait, what is this?’ Steve was able to speak a common language with them.”

The capital cost of ocean capture should be lower than that of air capture; in addition, using off-peak renewable electricity to run electrodialysis is expected to keep operating costs down, according to Oldham. Captura is targeting a removal cost of $100 per metric ton of CO₂.

For now, the firm is using its $45.3 million in series A funds to quickly ramp up. A year ago, it started up a pilot facility on a World War II US Navy barge at the Port of Los Angeles that can capture 100 metric tons (t) of CO₂ annually. It is also building a 1,000 t per year facility—enough to offset emissions from about 200 cars—in partnership with the Norwegian energy firm Equinor that should open early next year at the Hawaii Ocean Science and Technology Park, an ocean research facility.

Oldham sees room for both DAC and DOC in the climate change fight—even though both remain unproven at large scale. “Every technology is unproven until it’s proven,” he says. “We’re in the process of proving that DOC works and could be cost effective. Then you’ll start seeing adoption.”