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Splitting Water For Fuel While Removing CO2 From the Air

An anonymous reader quotes a report from Ars Technica: A new study led by the University of California, Santa Cruz’s Greg Rau highlights another tool for our CO2 removal toolbox: splitting seawater to produce hydrogen gas for fuel while capturing CO2 with ocean chemistry. In electrolysis, a device powered by electricity is used to split H2O, producing hydrogen gas. Several chemical modifications to this process have been proposed that can also grab CO2 from the atmosphere. Like the idea of using biofuels, this represents a “win-win” by producing an energy resource while capturing CO2, bringing the cost down. [T]he gist is that atmospheric CO2 goes into the ocean as bicarbonate — which won’t acidify the water or harm ecosystems. So if you power the electrolysis process with renewable energy, you can turn solar/wind/hydroelectric energy into hydrogen fuel while also removing CO2 from the air.

The new study focuses on a basic estimate of the cost and maximum potential of this technique. First, the researchers worked out its efficiency of CO2 capture — about 0.3 tons captured per gigajoule of electricity input, including the losses from quarrying and crushing rock. That’s around 10 times greater than biofuel schemes, but it depends on the assumption that there is demand for all the hydrogen fuel you make. The hydrogen can be used by vehicles, and there’s the possibility of using hydrogen as a type of storage for the electric grid — using excess power to make hydrogen that can run a power plant when needed. So it’s not too farfetched that demand could rise to meet supply. The researchers’ back-of-the-envelope estimate puts the cost of this system at between $3 and $161 per ton of captured CO2, depending on which type of renewable energy powers it. The study has been published in the journal Nature Climate Change.

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