The sorbent molecule used in CCS is an amine, a derivative of ammonia. In CCS, exhaust is bubbled through an amine-containing solution, and the amine chemically binds the CO₂, removing it from the exhaust gases. The CO₂ — now in liquid form — is then separated from the amine and converted back to a gas for disposal.

In CCS, those last steps require high temperatures, which are attained using some of the electrical output of the power plant. Gallant wondered whether her team could instead use electrochemical reactions to separate the CO₂ from the amine — and then continue the reaction to make a solid, CO₂-containing product. If so, the disposal process would be simpler than it is for gaseous CO₂. The CO₂ would be more densely packed, so it would take up less space, and it couldn’t escape, so it would be safer. Better still, additional electrical energy could be extracted from the device as it discharges and forms the solid material. “The vision was to put a battery-like device into the power plant waste stream to sequester the captured CO₂ in a stable solid, while harvesting the energy released in the process,” says Gallant.