MIT researchers claim to have devised a method to release and capture CO2 from the ocean that uses less energy than direct air capture.

The scientists developed a system in which seawater is passed through two chambers. The first one turns dissolved inorganic bicarbonates into carbon dioxide gas by acidifying the water using reactive electrodes to release protons. The CO2 gas is collected through a vacuum. 

“Then the water’s pushed through to a second set of cells with a reversed voltage, calling those protons back in and turning the acidic water back to alkaline before releasing it back into the sea. Periodically, when the active electrode is depleted of protons, the polarity of the voltage is reversed, and the same reaction continues with water flowing in the opposite direction,” wrote Loz Blain in New Atlas.

Previous methods of capturing CO2 have involved expensive membranes and a constant stream of chemicals. The MIT team’s system uses neither. 

Pulling CO2 emissions from the atmosphere through direct air capture is an expensive and energy-intensive process. The ocean is the earth’s number one carbon sink, soaking up 30-40% of the world’s annual carbon emissions. When CO2 is removed from the ocean, it can suck more of the greenhouse gas out. 

In the study published in the peer-reviewed journal Energy & Environmental Science, the team claims its system requires an energy input of 122 kJ/mol. They also said that the energy consumed in the process can be lowered further.: “Though our base energy consumption of 122 kJ/mol-CO2 is a record-low,” stated the study. “It may still be substantially decreased towards the thermodynamic limit of 32 kJ/mol-CO2.”   

The team estimates a cost of around US$56 per ton of CO2. The study mentions that the calculated cost does not consider auxiliary costs outside of the electrochemical system. According to the team, some of the costs can be mitigated by utilizing carbon capture units.