Seawater could be a source of clean hydrogen fuel
Tamara Kulikova / Alamy
For the first time, electrodes capable of producing hydrogen from seawater without producing corrosive and toxic chlorine gas have been produced on a commercial scale.
“Traditional electrolysis is only possible with pure water, an increasingly scarce global resource,” Doug Wicks of the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) said in a press release. “(These electrodes) eliminate the process’s reliance on pure water and instead utilize the world’s most abundant water resource: the ocean.”
The process uses negatively charged cathodes and positively charged anodes to split seawater into four “streams”: useful oxygen and hydrogen, and harmless acidic and alkaline streams that can easily be recycled back into the ocean. Equatic, a California startup that designed the technology with ARPA-E’s backing, plans to sell the hydrogen and oxygen produced in the process to offset costs. The alkaline stream reacts with atmospheric CO2 to form stable minerals that can be returned to the ocean, while the acidic stream can be returned to the ocean once it has returned to its original pH after flowing over silica-rich rocks.
Similar to the standard technology for splitting water to produce hydrogen, the process takes place in an electrolyser, a machine that uses a stack of electrodes to separate water molecules with electricity. But existing equipment has trouble working in seawater, which is full of dissolved salts, other minerals, metals and microorganisms that degrade components and interfere with operation. Also, the electrical charge that attracts oxygen to the anode separates the salts in the seawater, producing toxic chlorine gas that rapidly corrodes the machinery.
To get around this problem, Chen and his colleagues designed an anode that can selectively separate oxygen from water molecules without decomposing the salt. They used a chloride blocking layer to allow water to pass through the catalyst while keeping the salt out. Based on lab tests, Chen expects the anode to work for at least three years, after which it will need to be removed and recoated.
Pau Fallas of the University of Galway in Ireland, who is not affiliated with the company, says the three-year period is an impressive achievement, and that the oxygen-selective anode is a promising way to use seawater to make hydrogen fuel. But it hasn’t yet been proven to work in the field, he says. “What we need is to see real-world performance in a real environment,” he says.
The company will begin producing the anodes at a California factory with a capacity to produce 4,000 anodes per year for use in a demonstration plant it is building in Singapore that it says can remove 10 tonnes of CO2 and produce 300 kilograms of hydrogen per day.
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