Prototype captures ocean CO₂ while clearing mineral fouling

Inside a flow cell built from two 8-cm-tall plates, ocean water meets a redox salt on opposite sides of an ion-exchange membrane. The University of Michigan Engineering team has now shown that this prototype can pull carbon dioxide from the water and clear its own mineral deposits, a problem that has slowed earlier attempts to run oceanic carbon capture continuously.

The device works in alternating pH swings. Hydrogen gas starts the acidification phase, bringing the water to pH 4 and releasing carbon dioxide when the liquid is sprayed into an evacuated chamber. Reversing the electrodes then drives the basification phase to pH 10.7, producing hydrogen gas and restoring the redox salt. Afterward, the water can re-equilibrate with the atmosphere toward the natural baseline of pH 8.1 before the next cycle.

The cleaning effect appeared in simulated ocean water made with aquarium sea salt. Magnesium and calcium deposits covered 25% to 42% of the electrode after basification; starting the next cycle with acidification reduced coverage to about 7%. That amounts to 86% of fouling coverage removed without an acid wash or downtime. Across four cycles, energy intensity stayed constant, while prior approaches lost 67% of their performance by cycle four because of buildup.

The team also reshaped the salt channel with 1-mm-thick fins set at a 30-degree angle. The ridges swirl the liquid and deliver redox salt to the electrode faster, allowing a flow rate of 50 mL/min and a current density of 100 mA/cm², described by the researchers as industrial-scale.

So what changes in practice? A self-cleaning cell could make long-running ocean carbon capture less dependent on maintenance, while the captured carbon could be used in products such as concrete or jet fuel. Its electricity-producing and electricity-consuming phases could also shift load away from high-demand hours. But this remains a prototype: the researchers say its electrical resistance is 100 times too high for real-world deployment, and plan to replace the plastic plates with metal ones and bring the electrodes and membrane into near-zero-gap contact.