A Bismuth-Driven Flow-through pH Swing Architecture for Membrane-Free Seawater Carbon Removal

Unofficial AI-generated summary based on the public title and abstract. Not an official translation.

🔬研究者:Researchers in electrochemical CDR should note the flow-through electrode design and the importance of silver counter electrode cost reduction.

🏢実務担当者:Practitioners in carbon removal technology can use the technoeconomic analysis to evaluate cost drivers for scaling up bismuth-based pH swing systems.

🏛政策担当者:Policymakers should consider this technology as a promising marine CDR option with clear R&D needs for cost reduction.

Marine carbon dioxide removal (CDR) through electrochemical pH swings offers a promising pathway for scalable and durable CO₂ removal. Using seawater as a natural air-contactor and electrolyte, electrochemical modulation of seawater pH shifts the carbonate equilibrium to enable CO 2 release/capture from acidic/alkaline streams, with the sole input of electrical energy. Such pH modulation can be efficiently achieved through bismuth/bismuth oxychloride electrodes, which reversibly exchange protons in saline environments, though thus far implementation has been limited to modest reaction rates. Although this pH swing system avoids the expense of ion-exchange membranes, projected electrode material costs remain prohibitive at low reaction rates (1 mA/cm 2 ). While sufficient for low current density operation, the conventional planar electrode flow-by cell configuration of prior work faces limitations in high-throughput operation, as losses associated with the electrode gap, interfacial area, and electrolyte flow path are amplified. Here, we advance this bismuth-based system to industrially relevant current densities by developing a flow-through pH swing cell designed for elevated reaction rates. Porous flow-through electrodes are fabricated by coating active materials onto high-surface-area porous graphite felt substrates, providing both large electroactive area and through-plane electrolyte permeability. Isolated electrode characterization is used to guide development and identify desired process parameters for material-efficient performance. Integrated flow cell testing demonstrates an order-of-magnitude increase in current density over prior studies with minimal energy penalty, operating at 0.7 V at 20 mA/cm² compared to ~0.6 V at 1 mA/cm² in previous work. The flow-through configuration reduces energy consumption by 22% relative to a planar flow-by cell tested for comparison at 20 mA/cm² and maintains superior performance when scaled up to 25 cm². Furthermore, the scaled-up cell exhibits consistent operation with both simulated seawater and real seawater after nanofiltration. Technoeconomic analysis is used to relate performance metrics to projected costs per ton of CO 2 as part of a 1 Mton/year plant. Analysis translates these flow-through electrode performance gains to a 16% projected cost reduction compared to the planar flow-by configuration of this work. Projected costs are dramatically reduced (>66%) over those based on the low current density operation of prior systems. Material-specific cost modeling identifies silver counter electrodes as the dominant expense (>90% of material cost), indicating that removal of silver is critical for realizing a cost-effective plant-scale system. Together, these results demonstrate that bismuth-based pH swing systems can attain high reaction rates with favorable energetics, achieving performance metrics needed for scalable, low-cost marine carbon removal. Figure 1

• semanticscholar https://doi.org/10.1149/ma2026-01281417mtgabsfirst seen 2026-07-20 05:29:16