Equipment to capture carbon dioxide from ambient air or smokestacks generally works through a sort of reversible filter. Air is passed through granules or a liquid that absorbs the CO2, then that CO2-loaded substance undergoes a process (usually heating) that causes it to let go of all that CO2. The resulting gas can be collected in a separated stream.
It’s also possible to do a similar sort of operation on a smaller scale—like inside a battery. A new study from a team led by James Buchen of the University of Delaware demonstrates an example of a battery-based electrochemical carbon-capture technique that they say is more viable than previous attempts. It has the potential to require less energy—and therefore be cheaper—than the reversible-filter designs that currently dominate.
The basic idea behind a device of this type is that hydroxide produced at the battery cathode reacts with CO2, converting it to carbonate or bicarbonate that passes through the separator membrane to the anode. There, the lower pH causes the reaction to reverse, with carbonate turning back into CO2 gas. The role of the cathode is to produce hydroxide ions; the role of the anode is to consume them.
In this case, both the cathode and anode are nickel hydroxide. That’s the same as the cathode in the old-school rechargeable AA and AAA nickel-metal hydride batteries. But instead of a battery you can charge full of energy to power some mobile device, this works more like a chemical seesaw.
Apply a voltage in one direction and you drive the cathode to make hydroxide that moves to the anode. Switch the applied voltage around, and the old anode becomes the new cathode, driving the exact same chemistry in reverse. And the whole time this device is grabbing CO2 and transporting it across the cell.
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