Oceans absorb about one-third of atmospheric carbon dioxide (CO₂) emissions, but removing the dissolved carbon from oceans and converting it into useful products remain a significant challenge. No existing system has successfully integrated direct ocean capture (DOC) with the direct conversion of CO₂ into a valuable chemical feedstock.

In a study published in Nature Catalysis, a team led by GAO Xiang from the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences, along with XIA Chuan from the University of Electronic Science and Technology of China, developed an artificial ocean carbon recycling system that captures CO₂ from seawater and directly converts it into succinic acid.

The proposed system combines electrochemistry with microbial fermentation in a unique cascade process. Seawater was introduced into a five-chamber electrochemical reactor where an applied electric field drove water splitting, generating protons that acidified the seawater in a targeted chamber. This pH shift efficiently converted dissolved carbonate species into gaseous CO₂. 

The CO₂ was then separated via a hollow-fiber membrane and delivered to a second reactor containing a custom-designed bismuth-based catalyst, which selectively reduced CO₂ to formic acid. The formic acid was fed to an engineered strain of Vibrio natriegens for microbial fermentation, yielding succinic acid as the final product, which is a key monomer for the biodegradable plastic polybutylene succinate.

The system showed exceptional performance. The five-chamber reactor continuously extracted CO₂ from natural seawater sourced from Shenzhen Bay, China, for over 530 hours, achieving a carbon capture efficiency of 70%. The estimated cost for the capture was approximately $230 per metric ton of CO₂, which is competitive with existing state-of-the-art carbon capture technologies.

By incorporating different engineered microbes, the proposed system can be tailored to produce a range of valuable industrial chemicals, such as lactic acid, alanine, and 1,4-butanediol.

"This is the first demonstration that's going from ocean CO₂ all the way to a usable feedstock for bioplastic. The true focal point is taking that CO₂ and turning it into a bioplastic monomer with promising stability and economics," commented XIANG Chengxiang, a specialist in chemical physics and materials science at the California Institute of Technology, who was not involved in the work.

This study demonstrates a sustainable strategy for upcycling ocean-derived CO₂, and opens new avenues for electrochemically driven biochemical synthesis.