Seawater could be a source of clean hydrogen
Tamara Kulikova / Alamy
For the first time, electrodes capable of producing hydrogen from seawater without generating corrosive and toxic chlorine gas will be produced on a commercial scale.
“Traditional electrolysis has only been possible with pure water, an increasingly scarce global resource,” Douglas Wicks at the U.S. Department of Energy’s Advanced Research Projects Agency (ARPA-E) said in a press release“(These electrodes) eliminate the process’s reliance on pure water and instead harness the world’s most abundant water resource: the ocean.”
The process uses a negatively charged cathode and a positively charged anode to split seawater into four “streams”: useful oxygen and hydrogen, and harmless acidic and alkaline streams that can be easily recycled back into the ocean. Equatic, the California startup that developed the technology with ARPA-E support, plans to sell the hydrogen and oxygen created in the process to offset its costs. The alkaline stream reacts with CO2 in the atmosphere to form stable minerals which can be discharged into the sea, while the acidic current can be returned to the ocean once it has regained a higher pH after flowing over silica-rich rocks.
Like conventional techniques for splitting water to produce hydrogen, this process takes place in an electrolyzer, a machine that uses stacks of electrodes to split water molecules using electricity. But existing devices struggle with seawater because it destroys them: it’s full of dissolved salt, other minerals, metals and microorganisms that degrade components and clog the mechanism. Plus, the electrical charge that attracts oxygen to the anode separates the salt from the seawater, generating toxic chlorine gas that quickly corrodes the machine.
To avoid this problem, Chen and his colleagues designed an anode that could selectively separate oxygen from water molecules without separating the salt. They used a chlorine-blocking layer to allow water to pass through the catalyst while stopping the salt. Based on lab tests, Chen says they expect the anodes to work for at least three years before they need to be removed and recoated.
Paul Farras Three years would be a good amount of time, and these oxygen-selective anodes are a promising approach to using seawater to produce hydrogen, according to a researcher at the University of Galway in Ireland, who is not involved in the company. But he adds that they have yet to be shown to work in nature. “What we need to do is see the actual performance in a real environment,” he says.
The company will now begin producing anodes at a plant in California capable of making 4,000 a year. They will be used in a demonstration plant under construction in Singapore, which the company says will be capable of removing 10 tonnes of CO2 and producing 300 kilograms of hydrogen per day.
