The Breakthrough That Could Unlock Ocean Carbon Removal

Since at least the 1970s, electrochemists have cast their gazes upon the world’s vast, briny seas and wondered how they could harness the endless supply of hydrogen locked within. Though it was technically possible to grab the hydrogen by running an electrical current through the water, the reaction turned the salt in the water into the toxic and corrosive gas chlorine, which made commercializing such a process challenging.

But last year, a startup called Equatic made a breakthrough that not only solves the chlorine problem, but has the potential to deliver a two-for-one solution: commercial hydrogen production and carbon removal. With funding from the Department of Energy’s Advanced Research Projects Agency-Energy, or ARPA-E, the company moved swiftly to scale its innovation, called an “oxygen-selective anode,” from the lab to the factory. On Thursday, it announced it had started manufacturing the anodes at a facility in San Diego.

“I want to emphasize how fast this has moved,” Doug Wicks, a program director at ARPA-E, told me. “They made some pretty large claims about what they could do, so we took it as a high risk project, and really within the first year, they were able to clearly demonstrate that they could make great progress.”

In 2021, Equatic’s co-founders Xin Chen and Gaurav Sant, who are researchers at the University of California, Los Angeles, applied for an ARPA-E grant to work on their idea for a hybrid system that would use seawater electrolysis — sending an electrical current through seawater — to sequester carbon dioxide from the air in the ocean while also producing hydrogen.

Setting aside the chlorine issue for a moment, the process of getting hydrogen out of water is pretty established science. The carbon removal part was new. To achieve it, they would exploit another aspect of the electrolytic reaction: It could separate the seawater into two streams — one very acidic, the other very alkaline and able to easily absorb CO2. If they exposed the alkaline stream to air, it would suck up CO2 like a sponge and convert it into a more stable molecule that couldn’t easily return to the atmosphere. Then they could feed the water back into the sea, enhancing the ocean’s natural carbon pump.

This approach to carbon removal has two big things going for it. First, by driving this reaction through a closed system on land, Equatic can measure the carbon sequestered much more precisely than related methods that are deployed in the open ocean. “You can count what comes in, you can count what goes out, you just have greater control,” David Koweek, the chief scientist at Ocean Visions, a nonprofit that advocates for ocean-based climate solutions, told me. But with that control comes a trade-off, Koweek said. It requires more infrastructure, energy, and operational complexity than something like adding antacids directly to the water. That’s where Equatic’s second advantage could help. Its process produces clean hydrogen, a valuable commodity, which can help defray the cost of the carbon removal.

“We're not just a one way street, only energy in — you actually get some energy out,” Edward Sanders, the company’s chief operating officer, told me. He provided some numbers: For every 2.5 megawatt-hours of electricity Equatic’s system consumes, it can remove 1 metric ton of carbon from the air and produce 1 megawatt-hour worth of energy in the form of hydrogen. The company can either use the hydrogen to help power its operations or sell it. Therefore, the net energy use is more like 1.5 megawatts, he said, which is lower than what a direct air capture plant, for example, requires. (A direct air capture plant using a solid sorbent needs about 2.6 megawatts per ton of CO2 removed, according to the International Energy Agency.) Energy accounts for about 70% of costs, Sanders said.

Equatic was able to prove its concept out in two small pilot projects deployed in the Los Angeles harbor and in Singapore that each removed about 100 kilograms of carbon from the air, and produced just a few kilograms of hydrogen, per day. But because of the chlorine issue, the two plants were expensive, using bespoke, corrosion-resistant materials. Sanders told me it would cost on the order of millions of dollars to manage the chlorine gas at scale. The company would need to find a more economic solution.

The formation of chlorine in seawater electrolysis is a problem that has stumped scientists for so long that it has split the electrochemists into two camps — those who still believe it’s solvable, and those who think it makes more sense to just purify the water first.

When I asked Chen what the day-to-day work of trying to overcome this looked like, he said it was materials science research. He needed to find the right combination of catalysts to make an anode — a sheet of conductive, positively-charged metal — that, when used in electrolysis, would screen out the salt and not allow it to react. “It’s like Gandalf holding the way to tell chlorine, ‘you shall not pass.’” he said. “That’s essentially how it works. Only water molecules can pass through.”

Chen and Sant were awarded $1 million from ARPA-E for the research in 2022. About a year later, they felt they were on to something. As with most scientific “breakthroughs,” there was no single moment of discovery — Chen was not even the first to do what he did, which was to use manganese oxide. “There’s a lot of literature that indicates it’s doable,” he told me. “There’s pioneering work by other scientists from almost 30 years ago, but they didn’t pursue it far enough because I don’t think the opportunity was right at that time.”

What Chen did was push to find an iteration that was more effective, durable, and affordable. He ultimately landed on a design that produced less than one part per million of chlorine — lower than the amount in drinking water — and performed reliably for more than 20,000 hours of testing. When he showed his progress to Wicks at ARPA-E, the agency was impressed enough to grant the scientists an additional $2 million. That funding helped them get their first production line up and running.

The facility in San Diego will be able to produce 4,000 anodes per year to start, and is expected to operate at full capacity by the end of 2024. It will produce the anodes for Equatic’s first demonstration-scale project, a new plant in Singapore designed to remove 10 metric tons of CO2 and produce 300 kilograms of hydrogen per day — 100 times larger than the pilot version. Equatic also has plans to build an even bigger plant in Quebec that can remove 300 tons per day. That’s about three times the capacity of Climeworks’ Mammoth plant, the world’s largest direct air capture plant operating today.

The manufacturing line will also be able to refurbish the anodes after about three years of use, simply by applying a new layer of catalysts. Wicks of ARPA-E told me this was a “breakthrough coating technique” that will allow the company to really decrease costs.

When I asked Wicks what he sees as the next milestones for Equatic, what will determine whether it will be successful, he said a lot was riding on the scale up in Singapore and Canada. The company has already signed an agreement to deliver 2,100 metric tons of hydrogen to Boeing and remove 62,000 metric tons of CO2 from the air on the aerospace giant’s behalf. The companies have not made the price of the deal public.

One challenge ahead will also be navigating the permitting environment in the different countries. Koweek of Ocean Visions told me that this kind of seawater chemistry modification was “relatively benign,” but he said there were still risks that had to be characterized.

In the meantime, Chen isn’t done trying to optimize his anode in the lab. I asked him how he felt after his initial discovery — were you excited? Did you celebrate?

“Not really,” he replied. “So I’m very excited inside. But I was generally thinking about it, can we push it further?”