In 2024, the stark reality of climate change was underscored as global average temperatures surpassed the critical threshold of 1.5°C above pre-industrial levels for the first time—a benchmark long upheld as a safeguard by the 2015 Paris Agreement. This milestone signals a watershed moment: emissions reductions alone are insufficient to reverse the environmental trajectory. Scientists and policymakers worldwide increasingly recognize the imperative to deploy carbon dioxide removal technologies (CDR), aimed at actively extracting CO₂ from the atmosphere at unprecedented scales. Projections from the International Energy Agency estimate that achieving net-zero global emissions by 2050 will necessitate the removal of approximately one billion tonnes of CO₂ annually, an amount equivalent to the entirety of global aviation emissions. The enormity of this challenge calls for a nuanced understanding and optimization of carbon capture approaches.
A recent collaborative study led by researchers at the Renewable and Sustainable Energy Institute (RASEI), including Professors Wilson Smith and Bri-Mathias Hodge, presents an incisive techno-economic comparison of two frontier methods for atmospheric carbon removal: direct air capture (DAC) and direct ocean capture (DOC). This work, published in the journal Joule, leverages integrated modeling frameworks to assess both technologies under an innovative regeneration strategy powered by bipolar membrane electrodialysis (BPMED), a promising electricity-driven process.
Direct air capture, the more mature of the two approaches, employs liquid solvents to scrub CO₂ directly from ambient air. Facilities like the under-construction plant in Texas, capable of capturing half a million tonnes of CO₂ annually, showcase the scalability potentials of DAC technology. In contrast, direct ocean capture capitalizes on the ocean’s natural propensity to absorb a substantial fraction of anthropogenic CO₂ emissions—roughly 30% per year. By extracting dissolved inorganic carbon from seawater, DOC circumvents the energy-intensive need to process vast quantities of dilute atmospheric air, leveraging the ocean’s carbon reservoir as a more concentrated carbon source.
A critical obstacle shared by both techniques is the regeneration of the sorbent medium, which conventionally requires thermal input near 900°C to release concentrated CO₂. This step not only demands significant energy, often sourced from fossil fuels, but also emits greenhouse gases that compromise the net efficacy of CO₂ removal. Recognizing this challenge, the RASEI team simulated replacing thermal regeneration with BPMED, wherein electrical currents drive chemical shifts to release CO₂ under ambient temperature conditions, potentially reducing energy consumption and emissions.
The study’s integrated techno-economic analysis (TEA) bridges physical capture mechanisms, energy expenses, and full cost implications, enabling a holistic understanding of scale-up feasibility. Lead author Dr. Hussain Almajed emphasizes the study’s goal to elucidate trade-offs rather than declare a definitive winner, contextualizing the comparison within varying energy grid scenarios, including current and projected decarbonized states of the California electricity grid as well as off-grid renewable power supplies.
Fundamental disparities in carbon concentration between air and seawater define the operational and economic characteristics of DAC versus DOC. While atmospheric CO₂ is exceedingly dilute—approximately 120 times less concentrated than dissolved carbon in seawater—once captured, the typical DAC solvent solution exhibits carbon concentrations 160 to 320 times higher than that of seawater. This means DAC systems process smaller liquid volumes but operate BPMED under high electrical currents, resulting in high energy consumption despite a more compact equipment footprint.
Conversely, DOC systems must handle vast volumes of seawater with low carbon content, necessitating membrane areas roughly 20 times larger than DAC facilities. Although this significantly elevates capital costs, the BPMED process for DOC runs at lower current densities, translating to decreased energy per tonne of CO₂ captured. In modeled scenarios for a plant capturing 100,000 tonnes of CO₂ annually, DAC-BPMED’s cost approximated $470 per tonne under California’s existing grid, while DOC-BPMED was near $1,500 per tonne, predominantly due to capital expenditure rather than operational energy use.
An unexpected insight emerged regarding the economic role of sodium hydroxide (NaOH), a co-product generated during BPMED regeneration. NaOH is a globally traded industrial chemical, valued at around $450 per tonne, serving industries from paper manufacturing to water treatment. The DOC process, by processing expansive seawater volumes, produces surplus NaOH beyond its operational needs. Modeling suggests that in a decarbonized energy future circa 2050, revenue from NaOH sales could wholly offset the CO₂ capture costs, potentially resulting in net profitability for DOC-BPMED.
Despite these promising indications, the researchers caution about market scale limitations. The global NaOH market’s size constrains how much of the carbon capture industry’s output it can absorb without saturation effects. Even if DOC-BPMED supplied 20% of 2050 NaOH demand, it would offset less than 0.1% of today’s global energy emissions. Nonetheless, this finding highlights the broader strategic potential of integrating carbon capture with valuable commodity production, a synergy already pursued by companies like Travertine Tech, which simultaneously captures CO₂ and manufactures commercially valuable phosphoric acid and cementitious materials.
The source and nature of electricity powering BPMED regeneration is a paramount factor influencing the sustainability and cost profile of these capture systems. Through four electricity scenarios—California’s current grid, a highly decarbonized 2050 projection, and dedicated off-grid wind and solar installations—the study elucidates that grid-connected systems currently outperform standalone renewables on cost efficiency. The continuous operation enabled by grid reliability dilutes capital costs compared to intermittent renewables, which lack integrated energy storage optimizations in the model, elevating capture costs per tonne.
These findings underscore a vital policy message: achieving effective carbon removal at scale is intricately linked to grid decarbonization. Clean, reliable electricity supply is not ancillary but foundational to deploying next-generation carbon capture technologies sustainably and economically.
While the study offers rich insights, the authors acknowledge areas for refinement. Advanced membrane material characterization, updated equipment cost data, and integration of hybrid energy systems with storage promise to sharpen future model fidelity. These enhancements yield not only more precise cost predictions but also strategic direction on research investments—such as efforts to increase seawater carbon concentration for DOC, which the study’s sensitivity analysis indicates could slash capture costs by up to 50%.
Ultimately, removing atmospheric carbon on a scale commensurate with global emissions reduction targets demands interdisciplinary approaches spanning chemistry, engineering, economics, and policy. This study’s comprehensive techno-economic framework demystifies the complex trade-offs that define carbon removal technologies, presenting an informed roadmap for optimizing research and deployment strategies. Recognizing bottlenecks, evaluating synergies with commodity markets, and embedding the carbon capture systems in the context of a clean energy grid are pivotal steps en route to meaningful climate mitigation.
Subject of Research: Carbon dioxide removal technologies; direct air capture and direct ocean capture using bipolar membrane electrodialysis.
Article Title: Comparative Techno-Economic Analysis of Electrically Regenerated Direct Air and Ocean Carbon Capture Systems.
News Publication Date: 10-Apr-2026
Web References:
- https://climate.copernicus.eu/copernicus-2024-first-year-exceed-15degc-above-pre-industrial-level
- https://www.iea.org/reports/net-zero-by-2050
- https://www.colorado.edu/rasei/wilson-smith
- https://www.colorado.edu/rasei/bri-mathias-hodge
- https://doi.org/10.1016/j.joule.2026.102424
- https://doi.org/10.1038/s41467-020-18232-y
- https://travertinetech.com
References:
Almajed, H., Smith, W., Hodge, B.-M., et al. (2026). Comparative Techno-Economic Analysis of Electrically Regenerated Direct Air and Ocean Carbon Capture Systems. Joule. DOI: 10.1016/j.joule.2026.102424.
Keywords:
Carbon capture, Direct air capture, Direct ocean capture, Bipolar membrane electrodialysis, Carbon dioxide removal, Techno-economic analysis, Climate change mitigation, Renewable energy integration, Sodium hydroxide co-production, Grid decarbonization.
