Clever Chemistry Could Capture Carbon Dioxide While Producing Hydrogen Fuel

Keeping the planet cool looks like it will take more than just reducing our carbon emissions. Scientists now say that holding climate to less than 3.6˚ F warming worldwide—the threshold for dangerous warming—will almost certainly require sucking greenhouse gases out of the atmosphere. That’s usually a costly proposition.

But yesterday, researchers painted a picture of how to do so and their scalable scheme has a doubly beautiful twist—they claim actually produces useful energy without breaking the bank. Perhaps it is possible to have your cake and eat it, too.

Carbonate found in many types of rocks could help suck carbon dioxide from the atmosphere at store it stably on the ocean floor.

The new method involves a well-established process wherein water is split into energy-rich hydrogen gas and sets of paired oxygen and hydrogen atoms called hydroxide ions. The latter is able to gobble up carbon dioxide from the air, but only up to a certain point. Hydroxide’s carbon appetite can be increased substantially, however, by adding a substance called carbonate that’s found in many sedimentary rocks like limestone. The carbonate reacts with the carbon dioxide to form a chemical called bicarbonate—one half of the compound that makes up baking soda.

To be truly carbon negative, the process would work like this: use renewable energy to split sea water and capture the hydrogen gas for later use. Then take carbonate dug up from the ground, mix it with the remaining hydroxide-rich seawater, and release it into the ocean where it pulls carbon dioxide out of the air.

This process is not the only way to produce energy while capturing carbon dioxide. Growing crops to turn them into biofuels would do the same, but it would also require huge tracts of land. The electrolysis-based strategy considered in this study can draw down ten times as much carbon as a biofuel approach at about the same cost, even after factoring in the energy needed to mine and crush large amounts of carbonate rock.

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This approach has a much smaller land footprint than biofuels, according to the study, and therefore could suck more carbon dioxide from the atmosphere.

However, the plan may have its own challenges. Here’s Scott Johnson at Ars Technica:

Quarrying rock has its own localized environmental impact, as could pumping all that extra bicarbonate into the ocean. But the researchers argue that the idea is worth studying much more closely. The more options for removing atmospheric CO₂ we work up, the more likely it is that one catches on when serious incentives finally arrive.

Another hiccup is that the plan assumes there will be a market for huge amounts of hydrogen gas, which can be tricky to transport and use. Transportation may not be as much of a concern, though, as hydrogen could be used to store energy produced by intermittent renewable sources, like wind turbines or solar panels, for later use. With the right incentives, this could be a missing ingredient for an electricity grid fully based on renewable energy.

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