Toward scalable electrochemical CO2 capture from air and oceanwater: a unified techno-economic framework and design guidelines

Electrochemical CO2 capture from air and oceanwater is promising, yet pathway choices are complicated by inconsistent assumptions and the lack of a unified link connecting cell physics to plant-level cost. As a result, it is still uncertain, under realistic constraints, how direct air capture (DAC), direct ocean capture (DOC), and desalination-integrated indirect ocean capture (IOC) compare in energy and cost. Here, we develop a unified framework, coupling carbonate chemistry, bipolar membrane electrodialysis (BPMED) stack losses, and vacuum stripping under common system boundaries, to quantify energy and levelized cost across DAC, DOC, and IOC. We show that vacuum stripping is essential for DOC and, in DAC, reduces the CO2-release onset charge by 88-fold, enabling efficient operation at low current densities. In DAC, vacuum stripping reduces electrochemical energy consumption by up to 88.0% and total system energy by up to 76.6%. Although DOC shows high energy costs for oceanwater intake and pre-treatment, IOC configurations that leverage existing desalination infrastructure offer significant reductions in system-level energy and cost. Our analysis identifies operating regimes where the marginal increase in electricity cost is offset by declining non-electricity costs, yielding distinct optima for each pathway. At industrial scale, the minimum levelized cost reaches $0.38/kg-CO2 for DAC with vacuum stripping and $0.55/kg-CO2 for IOC with vacuum stripping. This work establishes a comparative foundation for electrochemical CO2 capture from air and ocean, and provides quantitative guidance for pathway selection, device optimization, and site-specific deployment.