Review of CO2 extraction from seawater through non-electrochemical and electrochemical approaches.

As the most significant carbon sink on Earth, the ocean has been inevitably absorbing excess atmospheric CO2, leading to high concentration of CO2 that threatens marine life. Like emissions of greenhouse gases, this issue demands urgent attention. Hence, comprehensive investigation and comparison, including both non-electrochemical and electrochemical direct ocean capture (DOC) methods, are revealed in this review. The non-electrochemical approach utilizes specialized materials such as gas-permeable membranes (GPM), hollow fiber membrane contactors (HFMC), and ion exchange resins to extract CO2 from seawater. In contrast, the electrochemical method employs chemical reactions to generate H+ or OH- ions, which adjust the pH value of seawater to either release CO2 gas or precipitate carbonate, thereby removing dissolved carbon. This article comprehensively overviews each method, including the latest research findings, underlying principles, employed equipment, and performance metrics. Finally, the achievements, current gaps, corresponding perspectives, and potential solutions in CO2 capture from seawater are also proposed.