New Method Removes Carbon Dioxide from Seawater

The oceans soak up 30 to 40% of the carbon dioxide produced by human activities. As carbon dioxide concentrations increase in oceans, the overall health of ocean ecosystems deteriorates. For example, increased acidification of ocean waters can destroy coral reefs, while reduced carbon ion concentrations harms marine life. The ability to effectively remove CO₂ from seawater could help mitigate some of these negative effects.

One route to remove carbon dioxide from seawater is by adjusting its pH. CO₂ from the air dissolves in seawater as carbonic acid, which releases protons in equilibrium and speciates as bicarbonate and carbonate ions. By lowering the pH of the seawater sample — from ~8.1 (i.e., its normal pH) to less than 7 — the dissolved inorganic carbon (DIC) can be converted back to CO₂, and the CO₂ can then be removed under vacuum.

It is beneficial to adjust the pH without any additional chemicals, as they can be expensive and promote the formation of undesirable compounds. In addition, residual chemicals have the potential to affect marine eco-systems. Electrochemical approaches can overcome these challenges while still offering precise control (i.e., the reactions are driven by supplying electrons in a controllable manner). However, most attempts at electrochemical removal of CO₂ from seawater require bipolar membranes, which are expensive and could impede...