Researchers have developed a compact hollow-fiber electrode system that could help overcome key barriers to large-scale carbon dioxide removal from seawater.
Study: A Compact Hollow Fiber Electrode Assembly Architecture for Continuous Electrochemical Marine Carbon Dioxide Removal. Image Credit: Stephan Langhans/Shutterstock.com
By combining a porous stainless steel hollow-fiber cathode with a coaxial ion-exchange membrane and counter electrode, the continuous-flow device dramatically shortens ion-transport distances, cuts electrical resistance, and enables more than 80-90% removal of dissolved inorganic carbon from seawater.
The system maintained stable operation for more than 100 hours with minimal mineral fouling, while reducing the energy required for carbon mineralization, offering a potentially scalable route to permanent ocean-based CO2 removal.
Challenges in Electrochemical Marine Capture
Ocean-based carbon dioxide capture has garnered increasing interest as a way to mitigate atmospheric CO2 on a gigaton scale using the ocean’s vast dissolved inorganic carbon pool and buffering capacity.
Electrochemical direct ocean capture (e-DOC) offers a promising, scalable approach that induces pH swings electrochemically, converting dissolved inorganic carbon into stable mineral forms, notably calcium carbonate and magnesium hydroxide, which can sequester CO2 long-term.
Despite its potential, e-DOC deployment is hampered by reactor design challenges, including low fluid-electrode interface areas, substantial Ohmic losses due to long ionic transport distances, and mineral fouling that degrades performance.
Click here to download a PDF copy of this page
Hollow Fiber Electrode Fabrication
The research developed a hollow fiber electrode assembly (HFEA) that integrates a macroporous stainless steel hollow fiber cathode with a coaxial counter electrode and an ion-exchange membrane positioned in the fiber lumen. This design achieves sub-millimeter spacing (~1 mm) between electrodes, substantially reducing ionic transport pathways and Ohmic resistance.
Fabrication involved a scalable dry-jet wet-quench spinning process to produce polymer-bound stainless steel precursor fibers. These fibers underwent controlled thermal treatments, debinding at 600 °C and sintering at 1150 °C, in inert atmospheres of argon or hydrogen to yield mechanically robust, corrosion-resistant porous metallic hollow fibers with high electrochemically active surface area.
A tubular Nafion membrane was fabricated by rolling and annealing techniques to fit inside the hollow fiber lumen, creating a tightly sealed ion-conductive barrier. The counter electrode was similarly integrated coaxially inside this membrane to establish a compact two-electrode configuration.
Electrochemical evaluations were conducted under continuous-flow operation using both simulated seawater and natural Jeju lava seawater. Fresh anolyte was pumped into the fiber lumen while catholyte flowed across the external fiber shell.
Current densities were normalized to the geometric surface area of the hollow fiber cathode. Mineralization performance was assessed by measuring dissolved inorganic carbon (DIC) removal efficiencies, mineral precipitation, and examining cathode fouling over extended operation.
Characterization techniques included scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), mercury intrusion porosimetry, and inductively coupled plasma optical emission spectroscopy (ICP-OES) to analyze the fiber microstructure, surface chemistry, mineral phases formed, and changes in ionic composition in the electrolyte.
Electrochemical methods such as linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) probed redox behaviors, charge transport properties, and interfacial resistances.
Continuous Electrochemical Carbon Removal Performance
The hollow fiber electrode displayed a robust, interconnected porous structure with high surface area and excellent mechanical strength. Sintered stainless steel fibers maintained integrity and corrosion resistance during prolonged operation in seawater environments.
The coaxial integration of the cathode, membrane, and counter electrode produced a compact geometry with electrode spacing less than 1 mm. This configuration considerably minimized ionic transport lengths, decreasing Ohmic losses by roughly 50% compared to traditional planar H-cell designs, substantially reducing the electrical energy requirement for electrochemical mineralization.
Operational testing under continuous flow demonstrated that the HFEA system could consistently achieve DIC removal efficiencies exceeding 80–90%, with stable performance sustained beyond 100 hours in both simulated and natural seawater without significant fouling. The membrane effectively prevented the mineral scale buildup that typically plagues planar zero-gap or membrane electrode assembly reactors, enabling long-term operational durability.
The compact electrode geometry also improved hydroxide-ion generation kinetics and dissolved CO2 conversion, supporting rapid precipitation of CaCO3 and Mg(OH)2. XRD and SEM analyses confirmed typical mineral phases relevant to permanent carbon sequestration.
ICP-OES measurements revealed substantial removal of calcium and magnesium ions from the treated seawater, further underscoring effective mineralization.
Energy consumption metrics improved significantly, with roughly half the energy required per mole of CO2 mineralized compared to conventional systems. Production of valuable co-products, high-purity hydrogen gas at the anode and magnesium hydroxide, further enhances system economic viability by offsetting overall energy costs.
Simulation and modeling reinforced the benefits of reduced electrode spacing in minimizing resistance and improving reaction distribution along the fiber length. The use of stainless steel for the hollow fiber electrode combined electrochemical activity with durability, whereas the tubular Nafion membrane provided selective ionic transport while mitigating fouling risks.
Scalable Ocean Carbon Mineralization Insights
This work introduces a transformative hollow fiber electrode assembly architecture that systematically addresses fundamental limitations of existing electrochemical marine carbon capture technologies.
By integrating macroporous stainless steel hollow fibers with a coaxial membrane and counter electrode, the design achieves sub-millimeter electrode spacing, drastically reducing Ohmic losses and boosting energy efficiency in continuous seawater mineralization.
By combining scalable fiber manufacturing, advanced materials design, and innovative reactor engineering, this study establishes a versatile platform toward sustainable, high-throughput marine carbon dioxide removal.
Journal Reference
Park I., Lee Y. H., et al. (2026). A Compact Hollow Fiber Electrode Assembly Architecture for Continuous Electrochemical Marine Carbon Dioxide Removal. Advanced Energy Materials, e71205. DOI: 10.1002/aenm.71205, https://advanced.onlinelibrary.wiley.com/doi/10.1002/aenm.71205