Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as calcium carbonate), and/or produce a CO₂-reactive chemical base, e.g. sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate.

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as calcium carbonate), and/or produce a CO₂-reactive chemical base, e.g. sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate.

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as carbonate minerals), and/or produce a CO₂-reactive chemical base, e.g. sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate.

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as carbonate minerals), and/or produce a CO₂-reactive chemical base, e.g. sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate.

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as calcium carbonate), and/or produce a CO₂-reactive chemical base, e.g. sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate.

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as calcium carbonate), and/or produce a CO₂-reactive chemical base, e.g., sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate.

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as calcium carbonate), and/or produce a CO₂-reactive chemical base, e.g., sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate.

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as calcium carbonate), and/or produce a CO₂-reactive chemical base, e.g., sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate. 

Electrochemical carbon dioxide removal technologies from seawater, sometimes called “direct ocean capture” to draw comparisons with direct air capture, encompass both Electrodialytic and Electrolytic techniques that capture and remove dissolved inorganic carbon from seawater (either as CO₂ gas or as calcium carbonate), and/or produce a CO₂-reactive chemical base, e.g., sodium hydroxide (NaOH), that can be distributed in the surface ocean to ultimately consume atmospheric CO₂ and convert it to long-lived, dissolved, alkaline bicarbonate. 

Electrodialytic approaches are already commercial technologies used in applications such as whey demineralization, organic acids recovery, and desalination, among others.

The electrolytic production of H₂, O₂/Cl₂, hydroxide, and acid is a very mature technology that globally produces some 75 Mt of NaOH per year that is an essential reagent in a variety of important industrial processes (e.g., in food processing, soap production, pulp and paper, pharmaceuticals, etc.).

An electrolytic approach to precipitate calcium carbonate has recently been proposed. This approach electrochemically generates alkalinity in order to precipitate calcium carbonate, generating a potentially useful end product from the captured carbon. But, as described above, precipitation of calcium carbonate from seawater acidifies the seawater, reducing the ability of seawater to absorb CO₂ from air. This proposed pathway is at a technology readiness level of ~2, and thus needs more development before further consideration.

In electrodialytic approaches electricity provides the energy to rearrange the most common components of seawater, H₂O and NaCl, into acidic (hydrochloric acid; HCl) and basic (sodium hydroxide; NaOH) solutions.^[1]House, Kurt Zenz, Christopher H. House, Daniel P. Schrag, and Michael J. Aziz. “Electrochemical Acceleration of Chemical Weathering as an Energetically Feasible Approach to Mitigating Anthropogenic Climate Change.” Environmental Science & Technology 41, no. 24 (December 2007): 8464–70. https://doi.org/10.1021/es0701816. The acidic solution can then be used to strip dissolved inorganic carbon from seawater in the form of gaseous CO₂, or the basic solution can be used to strip the dissolved inorganic carbon by precipitating solid calcium carbonate.^[2]Production of calcium carbonate via electrodialysis results in the basic component becoming acidified. This acidic stream may need to be neutralized through addition of a base before being recombined. In addition, the basic component can be selectively added to seawater to draw additional CO₂ into the ocean to be stably stored as bicarbonate ions. Electrodialytic approaches are already commercial technologies used in applications such as whey demineralization, organic acids recovery, and desalination, among others.^[3]Bazinet, Laurent; Geoffroy, Thibaud R. 2020. "Electrodialytic Processes: Market Overview, Membrane Phenomena, Recent Developments and Sustainable Strategies" Membranes 10, no. 9: 221. https://doi.org/10.3390/membranes10090221

Electrolytic approaches split water and salt into hydrogen and oxygen and/or chlorine gases, and produce alkaline metal hydroxide (e.g., sodium hydroxide) and acid as byproducts.^[4]Rau, G.H., Willauer, H.D. & Ren, Z.J. The global potential for converting renewable electricity to negative-CO₂-emissions hydrogen. Nature Clim Change 8, 621–625 (2018). https://doi.org/10.1038/s41558-018-0203-0 When added to surface seawater, the hydroxide reacts with CO₂ in seawater to form dissolved alkaline bicarbonate. The resulting CO₂ undersaturation in surface seawater then forces atmospheric CO₂ to enter the ocean and be stored largely as long-lived seawater bicarbonate. The electrolytic production of H₂, O₂/Cl₂, hydroxide, and acid is a very mature technology that globally produces some 75 Mt of NaOH per year that is an essential reagent in a variety of important industrial processes (e.g., in food processing, soap production, pulp and paper, pharmaceuticals, etc.).^[5]Lakshmanan, S. and Murugesan, T. (2014) ‘The chlor-alkali process: Work in Progress’, Clean Technologies and Environmental Policy, 16(2), pp. 225–234.

An electrolytic approach to precipitate calcium carbonate has recently been proposed^[6]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 . This approach electrochemically generates alkalinity in order to precipitate calcium carbonate, generating a potentially useful end product from the captured carbon. But, as described above, precipitation of calcium carbonate from seawater acidifies the seawater, reducing the ability of seawater to absorb CO₂ from air. This proposed pathway is at a technology readiness level^[7]Mai, T. (2015) Technology Readiness Level, NASA. Brian Dunbar. Available at: http://www.nasa.gov/directorates/heo/scan/engineering/technology/txt_accordion1.html of ~2, and thus needs more development before further consideration.

In electrodialytic approaches electricity provides the energy to rearrange the most common components of seawater, H₂O and NaCl, into acidic (hydrochloric acid; HCl) and basic (sodium hydroxide; NaOH) solutions^[1]House, Kurt Zenz, Christopher H. House, Daniel P. Schrag, and Michael J. Aziz. “Electrochemical Acceleration of Chemical Weathering as an Energetically Feasible Approach to Mitigating Anthropogenic Climate Change.” Environmental Science & Technology 41, no. 24 (December 2007): 8464–70. https://doi.org/10.1021/es0701816. . The acidic solution can then be used to strip dissolved inorganic carbon from seawater in the form of gaseous CO₂, or the basic solution can be used to strip the dissolved inorganic carbon by precipitating solid calcium carbonate.^[2]Production of calcium carbonate via electrodialysis results in the basic component becoming acidified. This acidic stream may need to be neutralized through addition of a base before being recombined. In addition, the basic component can be selectively added to seawater to draw additional CO₂ into the ocean to be stably stored as bicarbonate ions. Electrodialytic approaches are already commercial technologies used in applications such as whey demineralization, organic acids recovery, and desalination, among others.^[3]Bazinet, Laurent; Geoffroy, Thibaud R. 2020. "Electrodialytic Processes: Market Overview, Membrane Phenomena, Recent Developments and Sustainable Strategies" Membranes 10, no. 9: 221. https://doi.org/10.3390/membranes10090221

Electrolytic approaches split water and salt into hydrogen and oxygen and/or chlorine gases, and produce alkaline metal hydroxide (e.g., sodium hydroxide) and acid as byproducts.^[4]Rau, G.H., Willauer, H.D. & Ren, Z.J. The global potential for converting renewable electricity to negative-CO₂-emissions hydrogen. Nature Clim Change 8, 621–625 (2018). https://doi.org/10.1038/s41558-018-0203-0 When added to surface seawater, the hydroxide reacts with CO₂ in seawater to form dissolved alkaline bicarbonate. The resulting CO₂ undersaturation in surface seawater then forces atmospheric CO₂ to enter the ocean and be stored largely as long-lived seawater bicarbonate. The electrolytic production of H₂, O₂/Cl₂, hydroxide, and acid is a very mature technology that globally produces some 75 Mt of NaOH per year that is an essential reagent in a variety of important industrial processes (e.g., in food processing, soap production, pulp and paper, pharmaceuticals, etc.).^[5]Lakshmanan, S. and Murugesan, T. (2014) ‘The chlor-alkali process: Work in Progress’, Clean Technologies and Environmental Policy, 16(2), pp. 225–234.

An electrolytic approach to precipitate calcium carbonate has recently been proposed^[6]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 . This approach electrochemically generates alkalinity in order to precipitate calcium carbonate, generating a potentially useful end product from the captured carbon. But, as described above, precipitation of calcium carbonate from seawater acidifies the seawater, reducing the ability of seawater to absorb CO₂ from air. This proposed pathway is at a technology readiness level^[7]Mai, T. (2015) Technology Readiness Level, NASA. Brian Dunbar. Available at: http://www.nasa.gov/directorates/heo/scan/engineering/technology/txt_accordion1.html of ~2, and thus needs more development before further consideration.

In electrodialytic approaches electricity provides the energy to rearrange the most common components of seawater, H₂O and NaCl, into acidic (hydrochloric acid; HCl) and basic (sodium hydroxide; NaOH) solutions^[1]House, Kurt Zenz, Christopher H. House, Daniel P. Schrag, and Michael J. Aziz. “Electrochemical Acceleration of Chemical Weathering as an Energetically Feasible Approach to Mitigating Anthropogenic Climate Change.” Environmental Science & Technology 41, no. 24 (December 2007): 8464–70. https://doi.org/10.1021/es0701816. . The acidic solution can then be used to strip dissolved inorganic carbon from seawater in the form of gaseous CO₂, or the basic solution can be used to strip the dissolved inorganic carbon by precipitating solid calcium carbonate^[2]Production of calcium carbonate via electrodialysis results in the basic component becoming acidified. This acidic stream may need to be neutralized through addition of a base before being recombined. . In addition, the basic component can be selectively added to seawater to draw additional CO₂ into the ocean to be stably stored as bicarbonate ions. Electrodialytic approaches are already commercial technologies used in applications such as whey demineralization, organic acids recovery, and desalination, among others^[3]Bazinet, Laurent; Geoffroy, Thibaud R. 2020. "Electrodialytic Processes: Market Overview, Membrane Phenomena, Recent Developments and Sustainable Strategies" Membranes 10, no. 9: 221. https://doi.org/10.3390/membranes10090221 .

Electrolytic approaches split water and salt into hydrogen and oxygen and/or chlorine gases, and produce alkaline metal hydroxide (e.g., sodium hydroxide) and acid as byproducts^[4]Rau, G.H., Willauer, H.D. & Ren, Z.J. The global potential for converting renewable electricity to negative-CO₂-emissions hydrogen. Nature Clim Change 8, 621–625 (2018). https://doi.org/10.1038/s41558-018-0203-0 . When added to surface seawater, the hydroxide reacts with CO₂ in seawater to form dissolved alkaline bicarbonate. The resulting CO₂ undersaturation in surface seawater then forces atmospheric CO₂ to enter the ocean and be stored largely as long-lived seawater bicarbonate. The electrolytic production of H₂, O₂/Cl₂, hydroxide, and acid is a very mature technology that globally produces some 75 Mt of NaOH per year that is an essential reagent in a variety of important industrial processes (e.g., in food processing, soap production, pulp and paper, pharmaceuticals, etc.).^[5]Lakshmanan, S. and Murugesan, T. (2014) ‘The chlor-alkali process: Work in Progress’, Clean Technologies and Environmental Policy, 16(2), pp. 225–234.

An electrolytic approach to precipitate calcium carbonate has recently been proposed^[6]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 . This approach electrochemically generates alkalinity in order to precipitate calcium carbonate, generating a potentially useful end product from the captured carbon. But, as described above, precipitation of calcium carbonate from seawater acidifies the seawater, reducing the ability of seawater to absorb CO₂ from air. This proposed pathway is at a technology readiness level^[7]Mai, T. (2015) Technology Readiness Level, NASA. Brian Dunbar. Available at: http://www.nasa.gov/directorates/heo/scan/engineering/technology/txt_accordion1.html of ~2, and thus needs more development before further consideration.

In electrodialytic approaches electricity provides the energy to rearrange the most common components of seawater, H₂O and NaCl, into acidic (hydrochloric acid; HCl) and basic (sodium hydroxide; NaOH) solutions. The acidic solution can then be used to strip dissolved inorganic carbon from seawater in the form of gaseous CO₂, or the basic solution can be used to strip the dissolved inorganic carbon by precipitating solid calcium carbonate. In addition, the basic component can be selectively added to seawater to draw additional CO₂ into the ocean to be stably stored as bicarbonate ions. Electrodialytic approaches are already commercial technologies used in applications such as whey demineralization, organic acids recovery, and desalination, among others.

Electrolytic approaches split water and salt into hydrogen and oxygen and/or chlorine gases, and produce alkaline metal hydroxide (e.g., sodium hydroxide) and acid as byproducts. When added to surface seawater, the hydroxide reacts with CO₂ in seawater to form dissolved alkaline bicarbonate. The resulting CO₂ undersaturation in surface seawater then forces atmospheric CO₂ to enter the ocean and be stored largely as long-lived seawater bicarbonate. The electrolytic production of H₂, O₂/Cl₂, hydroxide, and acid is a very mature technology that globally produces some 75 Mt of NaOH per year that is an essential reagent in a variety of important industrial processes (e.g., in food processing, soap production, pulp and paper, pharmaceuticals, etc.).

An electrolytic approach to precipitate calcium carbonate has recently been proposed. This approach electrochemically generates alkalinity in order to precipitate calcium carbonate, generating a potentially useful end product from the captured carbon. But, as described above, precipitation of calcium carbonate from seawater acidifies the seawater, reducing the ability of seawater to absorb CO₂ from air. This proposed pathway is at a technology readiness level of ~2, and thus needs more development before further consideration.

• Scalability - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
• • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered.
    • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater, and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂
    • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs
    • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture.
  • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR.

Ranges from recent synthesis reports vary with the 2021 NASEM report suggesting a range of 0.1-1.0 Gt CO₂/yr with medium confidence, while the 2020 synthesis report from the Energy Futures Initiative suggests a potential range of 1-5 Gt CO₂/yr using the "Seawater carbon extraction pathway".

• Sequestration Permanence - Electrochemical methods that produce reactive alkaline minerals (e.g., NaOH) will result in additional CO₂ from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere. This is the same process that results in CO₂ sequestration for rock-based forms of ocean alkalinity enhancement. The residence time of bicarbonate ions in the ocean is ~10,000 years, suggesting that electrochemical alkalinity production will generate CO₂ sequestration with permanence of ~10,000 years.

Electrochemical methods that produce carbonate mineral products (e.g., ref) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

• Scalability - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt^[1]Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. ), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
• • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered^[2]Campione, A., L. Gurreri, M. Ciofalo, G. Micale, A. Tamburini, and A. Cipollina. “Electrodialysis for Water Desalination: A Critical Assessment of Recent Developments on Process Fundamentals, Models and Applications.” Desalination 434 (May 2018): 121–60. https://doi.org/10.1016/j.desal.2017.12.044. .
    • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater^[3]Eisaman, Matthew D., Jessy L.B. Rivest, Stephen D. Karnitz, Charles-François de Lannoy, Arun Jose, Richard W. DeVaul, and Kathy Hannun. “Indirect Ocean Capture of Atmospheric CO₂: Part II. Understanding the Cost of Negative Emissions.” International Journal of Greenhouse Gas Control 70 (March 2018): 254–61. https://doi.org/10.1016/j.ijggc.2018.02.020. , and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂^[4]Eisaman, Matthew D. “Negative Emissions Technologies: The Tradeoffs of Air-Capture Economics.” Joule 4, no. 3 (March 2020): 516–20. https://doi.org/10.1016/j.joule.2020.02.007
    • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs^[5]Rau, G.H. (2021) ‘Testimony to The National Academies of Sciences, Engineering, and Medicine: A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration’ 27-January-2021.
    • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture^[6]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 .
  • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR.

Ranges from recent synthesis reports vary with the 2021 NASEM report ^[7]National Academies of Sciences, Engineering, and Medicine. 2022. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278. suggesting a range of 0.1-1.0 Gt CO₂/yr with medium confidence, while the 2020 synthesis report from the Energy Futures Initiative suggests a potential range of 1-5 Gt CO₂/yr using the "Seawater carbon extraction pathway". ^[8]Energy Futures Initiative. “Uncharted Waters: Expanding the Options for Carbon Dioxide Removal in Coastal and Ocean Environments.” December 2020.

• Sequestration Permanence - Electrochemical methods that produce reactive alkaline minerals (e.g., NaOH) will result in additional CO₂ from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere. This is the same process that results in CO₂ sequestration for rock-based forms of ocean alkalinity enhancement. The residence time of bicarbonate ions in the ocean is ~10,000 years, suggesting that electrochemical alkalinity production will generate CO₂ sequestration with permanence of ~10,000 years.

Electrochemical methods that produce carbonate mineral products (e.g., ref^[9] Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 ) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

• Scalability - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
• • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered.
    • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater, and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂
    • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs
    • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture.
  • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR.

Ranges from recent synthesis reports vary with the 2021 NASEM report suggesting a range of 0.1-1.0 Gt CO₂/yr with medium confidence, while the 2020 synthesis report from the Energy Futures Initiative suggests a potential range of 1-5 Gt CO₂/yr using the "Seawater carbon extraction pathway".

• Sequestration Permanence - Electrochemical methods that produce reactive alkaline minerals (e.g., NaOH) will result in additional CO₂ from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere. This is the same process that results in CO₂ sequestration for rock-based forms of ocean alkalinity enhancement. The residence time of bicarbonate ions in the ocean is ~10,000 years, suggesting that electrochemical alkalinity production will generate CO₂ sequestration with permanence of ~10,000 years.

Electrochemical methods that produce carbonate mineral products (e.g., ref) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

1. Scalability - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt^[1]Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. ), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
   • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered^[2]Campione, A., L. Gurreri, M. Ciofalo, G. Micale, A. Tamburini, and A. Cipollina. “Electrodialysis for Water Desalination: A Critical Assessment of Recent Developments on Process Fundamentals, Models and Applications.” Desalination 434 (May 2018): 121–60. https://doi.org/10.1016/j.desal.2017.12.044. .
     • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater^[3]Eisaman, Matthew D., Jessy L.B. Rivest, Stephen D. Karnitz, Charles-François de Lannoy, Arun Jose, Richard W. DeVaul, and Kathy Hannun. “Indirect Ocean Capture of Atmospheric CO₂: Part II. Understanding the Cost of Negative Emissions.” International Journal of Greenhouse Gas Control 70 (March 2018): 254–61. https://doi.org/10.1016/j.ijggc.2018.02.020. , and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂^[4]Eisaman, Matthew D. “Negative Emissions Technologies: The Tradeoffs of Air-Capture Economics.” Joule 4, no. 3 (March 2020): 516–20. https://doi.org/10.1016/j.joule.2020.02.007
     • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs^[5]Rau, G.H. (2021) ‘Testimony to The National Academies of Sciences, Engineering, and Medicine: A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration’ 27-January-2021.
     • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture^[6]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 .
   • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR.

Electrochemical methods that produce carbonate mineral products (e.g., ref{{9}}) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

1. Carbon Capture - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt^[1]Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. ), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
   • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered^[2]Campione, A., L. Gurreri, M. Ciofalo, G. Micale, A. Tamburini, and A. Cipollina. “Electrodialysis for Water Desalination: A Critical Assessment of Recent Developments on Process Fundamentals, Models and Applications.” Desalination 434 (May 2018): 121–60. https://doi.org/10.1016/j.desal.2017.12.044. .
     • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater^[3]Eisaman, Matthew D., Jessy L.B. Rivest, Stephen D. Karnitz, Charles-François de Lannoy, Arun Jose, Richard W. DeVaul, and Kathy Hannun. “Indirect Ocean Capture of Atmospheric CO₂: Part II. Understanding the Cost of Negative Emissions.” International Journal of Greenhouse Gas Control 70 (March 2018): 254–61. https://doi.org/10.1016/j.ijggc.2018.02.020. , and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂^[4]Eisaman, Matthew D. “Negative Emissions Technologies: The Tradeoffs of Air-Capture Economics.” Joule 4, no. 3 (March 2020): 516–20. https://doi.org/10.1016/j.joule.2020.02.007
     • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs^[5]Rau, G.H. (2021) ‘Testimony to The National Academies of Sciences, Engineering, and Medicine: A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration’ 27-January-2021.
     • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture^[6]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 .
   • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR. 
2. Sequestration Permanence - Electrochemical methods that produce reactive alkaline minerals (e.g., NaOH) will result in additional CO₂ from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere. This is the same process that results in CO₂ sequestration for rock-based forms of ocean alkalinity enhancement. The residence time of bicarbonate ions in the ocean is ~10,000 years, suggesting that electrochemical alkalinity production will generate CO₂ sequestration with permanence of ~10,000 years.

   Electrochemical methods that produce carbonate mineral products (e.g., ref^[7] Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 ) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

   Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

1. Carbon Capture - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt^[1]Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. ), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
   • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered^[2]Campione, A., L. Gurreri, M. Ciofalo, G. Micale, A. Tamburini, and A. Cipollina. “Electrodialysis for Water Desalination: A Critical Assessment of Recent Developments on Process Fundamentals, Models and Applications.” Desalination 434 (May 2018): 121–60. https://doi.org/10.1016/j.desal.2017.12.044. .
     • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater^[3]Eisaman, Matthew D., Jessy L.B. Rivest, Stephen D. Karnitz, Charles-François de Lannoy, Arun Jose, Richard W. DeVaul, and Kathy Hannun. “Indirect Ocean Capture of Atmospheric CO₂: Part II. Understanding the Cost of Negative Emissions.” International Journal of Greenhouse Gas Control 70 (March 2018): 254–61. https://doi.org/10.1016/j.ijggc.2018.02.020. , and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂^[4]Eisaman, Matthew D. “Negative Emissions Technologies: The Tradeoffs of Air-Capture Economics.” Joule 4, no. 3 (March 2020): 516–20. https://doi.org/10.1016/j.joule.2020.02.007
     • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs^[5]Rau, G.H. (2021) ‘Testimony to The National Academies of Sciences, Engineering, and Medicine: A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration’ 27-January-2021.
     • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture^[6]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 .
   • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR. 
2. Sequestration Permanence Electrochemical methods that produce reactive alkaline minerals (e.g., NaOH) will result in additional CO₂ from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere. This is the same process that results in CO₂ sequestration for rock-based forms of ocean alkalinity enhancement. The residence time of bicarbonate ions in the ocean is ~10,000 years, suggesting that electrochemical alkalinity production will generate CO₂ sequestration with permanence of ~10,000 years.

   Electrochemical methods that produce carbonate mineral products (e.g., ref^[7] Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 ) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

   Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

1. Carbon Capture - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt^[1]Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. ), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
   • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered^[2]Campione, A., L. Gurreri, M. Ciofalo, G. Micale, A. Tamburini, and A. Cipollina. “Electrodialysis for Water Desalination: A Critical Assessment of Recent Developments on Process Fundamentals, Models and Applications.” Desalination 434 (May 2018): 121–60. https://doi.org/10.1016/j.desal.2017.12.044. .
     • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater^[3]Eisaman, Matthew D., Jessy L.B. Rivest, Stephen D. Karnitz, Charles-François de Lannoy, Arun Jose, Richard W. DeVaul, and Kathy Hannun. “Indirect Ocean Capture of Atmospheric CO₂: Part II. Understanding the Cost of Negative Emissions.” International Journal of Greenhouse Gas Control 70 (March 2018): 254–61. https://doi.org/10.1016/j.ijggc.2018.02.020. , and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂^[4]Eisaman, Matthew D. “Negative Emissions Technologies: The Tradeoffs of Air-Capture Economics.” Joule 4, no. 3 (March 2020): 516–20. https://doi.org/10.1016/j.joule.2020.02.007
     • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs^[5]Eisaman, Matthew D. “Negative Emissions Technologies: The Tradeoffs of Air-Capture Economics.” Joule 4, no. 3 (March 2020): 516–20. https://doi.org/10.1016/j.joule.2020.02.007
     • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture^[6]Rau, G.H. (2021) ‘Testimony to The National Academies of Sciences, Engineering, and Medicine: A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration’ 27-January-2021. .
   • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR. 
2. Sequestration PermanenceElectrochemical methods that produce reactive alkaline minerals (e.g., NaOH) will result in additional CO₂ from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere. This is the same process that results in CO₂ sequestration for rock-based forms of ocean alkalinity enhancement. The residence time of bicarbonate ions in the ocean is ~10,000 years, suggesting that electrochemical alkalinity production will generate CO₂ sequestration with permanence of ~10,000 years.

   Electrochemical methods that produce carbonate mineral products (e.g., ref^[7] Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 ) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

   Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

1. Carbon Capture - Given the immense stocks of dissolved inorganic carbon in seawater (~38,000 Gt^[1]Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. ), the theoretical scale of carbon capture from electrochemical methods is limitless for all practical intents and purposes. However, engineering, economic, political, and social considerations are likely to significantly reduce this upper bound. These include, but are not limited to:
   • Access to low or zero-carbon emissions energy and infrastructure (e.g., desalination plants, offshore wind) with the ability to pump large quantities of seawater into large-scale electrochemical reaction cells, perform electrodialysis or electrolysis, and capture outputs and byproducts. The exact energy and infrastructure needs are pathway-dependent. For instance, electrolysis requires more energy than does electrodialysis, but the relative value of beneficial products (e.g., H₂, O₂ in electrolysis, HCl in electrodialysis) produced by each process must also be considered^[2]Campione, A., L. Gurreri, M. Ciofalo, G. Micale, A. Tamburini, and A. Cipollina. “Electrodialysis for Water Desalination: A Critical Assessment of Recent Developments on Process Fundamentals, Models and Applications.” Desalination 434 (May 2018): 121–60. https://doi.org/10.1016/j.desal.2017.12.044. .
     • In the cases where electrodialysis is used to produce HCl and strip CO₂ gas out of seawater or used to produce NaOH that precipitates calcium carbonate, the cost is high (>$350/ton CO₂) because of the cost of pumping seawater^[3]Eisaman, Matthew D., Jessy L.B. Rivest, Stephen D. Karnitz, Charles-François de Lannoy, Arun Jose, Richard W. DeVaul, and Kathy Hannun. “Indirect Ocean Capture of Atmospheric CO₂: Part II. Understanding the Cost of Negative Emissions.” International Journal of Greenhouse Gas Control 70 (March 2018): 254–61. https://doi.org/10.1016/j.ijggc.2018.02.020. , and in the case of CO₂ stripping, the additional cost of safely storing or utilizing the captured CO₂^[4]Eisaman, Matthew D. “Negative Emissions Technologies: The Tradeoffs of Air-Capture Economics.” Joule 4, no. 3 (March 2020): 516–20. https://doi.org/10.1016/j.joule.2020.02.007
     • Costs can be lowered to ~$100/ton CO₂ if captured CO₂ is stored in the ocean as bicarbonate due to the elimination of seawater pumping costs
     • Electrolytic pathways may offer CDR for $150-100/ton CO₂, depending upon whether revenues generated from co-products are used to offset gross costs of CO₂ capture^[5]Rau, G.H. (2021) ‘Testimony to The National Academies of Sciences, Engineering, and Medicine: A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration’ 27-January-2021. .
   • The collective market size for suite of co-products and services offered, including concentrated CO₂, H₂, O₂, HCl, control over critical seawater chemistry parameters like pH and total alkalinity, and CDR. 
2. Sequestration PermanenceElectrochemical methods that produce reactive alkaline minerals (e.g., NaOH) will result in additional CO₂ from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere. This is the same process that results in CO₂ sequestration for rock-based forms of ocean alkalinity enhancement. The residence time of bicarbonate ions in the ocean is ~10,000 years, suggesting that electrochemical alkalinity production will generate CO₂ sequestration with permanence of ~10,000 years.

   Electrochemical methods that produce carbonate mineral products (e.g., ref^[6] Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 ) with sequestered carbon are stable on timescales of hundreds-to-thousands of years. 

   Electrochemical methods which capture and remove CO₂ gas from seawater have variable permanence depending upon the storage location for the captured CO₂. If the captured CO₂ is sequestered in geologic storage, permanence can be long (thousands-to-millions of years)

• Electrochemical CDR would likely provide localized reductions in ocean acidification, with expected benefit(s) to marine ecosystems.
• Carbon-negative byproducts from electrochemical CDR can be substituted for more C-intensive sources^[1]Rau, Greg H. “Electrochemical Splitting of Calcium Carbonate to Increase Solution Alkalinity: Implications for Mitigation of Carbon Dioxide and Ocean Acidity.” Environmental Science & Technology 42, no. 23 (December 2008): 8935–40. https://doi.org/10.1021/es800366q. :
  • Electrolysis: hydrogen gas, chlorine gas, and oxygen gas, as well as hydrochloric acid
  • Electrodialysis: hydrochloric acid
• In comparison to rock-based forms of alkalinity enhancement, electrochemical methods may offer:
  • Reduced risk of toxicity from metals present in rock-based forms of alkalinity addition^[2]Hartmann, J., A. J. West, P. Renforth, P. Köhler, C. L. De La Rocha, D. A. Wolf-Gladrow, H. H. Dürr, and J. Scheffran (2013), Enhanced chemical weathering as a geoengineering strategy to reduce atmospheric carbon dioxide, supply nutrients, and mitigate ocean acidification, Rev. Geophys., 51, 113–149, doi:10.1002/rog.20004. .
  • However, the purity of outputs from electrochemical CDR is determined partially by the purity of the input materials to the electrochemical processes, and purer input materials are more expensive.
  • Unlike ocean liming and coastal enhanced weathering, electrochemical alkalinity additions will not increase the silica concentration in the ocean and, therefore, may offer a reduced risk of disturbing phytoplankton community dynamics between calcifiers and silicifiers^[3]Bach LT, Gill SJ, Rickaby REM, Gore S and Renforth P (2019) CO₂ Removal With Enhanced Weathering and Ocean Alkalinity Enhancement: Potential Risks and Co-benefits for Marine Pelagic Ecosystems. Front. Clim. 1:7. doi: 10.3389/fclim.2019.00007 .

• Electrochemical CDR would likely provide localized reductions in ocean acidification, with expected benefit(s) to marine ecosystems.
• Carbon-negative byproducts from electrochemical CDR can be substituted for more C-intensive sources:
  • Electrolysis: hydrogen gas, chlorine gas, and oxygen gas, as well as hydrochloric acid
  • Electrodialysis: hydrochloric acid
• In comparison to rock-based forms of alkalinity enhancement, electrochemical methods may offer:
  • Reduced risk of toxicity from metals present in rock-based forms of alkalinity addition.
  • However, the purity of outputs from electrochemical CDR is determined partially by the purity of the input materials to the electrochemical processes, and purer input materials are more expensive.
  • Unlike ocean liming and coastal enhanced weathering, electrochemical alkalinity additions will not increase the silica concentration in the ocean and, therefore, may offer a reduced risk of disturbing phytoplankton community dynamics between calcifiers and silicifiers.

1. Risks Shared by Electrolysis and Electrodialysis
   • The potential for changes in water column particle concentrations, turbidity, and optical properties if precipitation (inorganic mineral formation) of carbonates occurs due to local increases in alkalinity and pH.  
   • Mortality of marine life through seawater intake pumps and filters
   • Shifts in phytoplankton, invertebrate and vertebrate physiology, competition and/or mortality due to decreases in acidity as CO₂ is removed and/or alkalinity is added.^[1]Renforth, P., and G. Henderson (2017), Assessing ocean alkalinity for carbon sequestration, Rev. Geophys., 55, 636–674, doi:10.1002/2016RG000533. For example, do the preceding seawater chemistry changes provide an increased competitive advantage for calcifiers over and above the restoration of calcifiers/calcification from ongoing ocean acidification?
   • Risks about permanence and impacts of elevated concentrations of bicarbonate in the oceans.
2. Risks Specific to Electrolysis
   • Chlorine gas production and handling
3. Risks Specific to Electrodialysis
   • Production of large quantities of acid via electrodialysis that must be safely consumed or neutralized (e.g., via reaction with alkaline minerals).
   • For pathways that strip CO₂ gas from seawater and sequester the CO₂, risks of permanence of storage and potential for leakage
   • For pathways that remove dissolved inorganic carbon from seawater as calcium carbonate^[2]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 , impacts of large quantities of new calcium carbonate on diversity, abundance, and ecosystem function of marine environments

1. Risks Shared by Electrolysis and Electrodialysis
   • The potential for changes in water column particle concentrations, turbidity, and optical properties if precipitation (inorganic mineral formation) of carbonates occurs due to local increases in alkalinity and pH.  
   • Mortality of marine life through seawater intake pumps and filters
   • Shifts in phytoplankton, invertebrate and vertebrate physiology, competition and/or mortality due to decreases in acidity as CO₂ is removed and/or alkalinity is added.^[1]Renforth, P., and G. Henderson (2017), Assessing ocean alkalinity for carbon sequestration, Rev. Geophys., 55, 636–674, doi:10.1002/2016RG000533. For example, do the preceding seawater chemistry changes provide an increased competitive advantage for calcifiers over and above the restoration of calcifiers/calcification from ongoing ocean acidification?
   • Risks about permanence and impacts of elevated concentrations of bicarbonate in the oceans.
2. Risks Specific to Electrolysis
   • Chlorine gas production and handling
3. Risks Specific to Electrodialysis
   • Production of large quantities of acid via electrodialysis that must be safely consumed or neutralized (e.g., via reaction with alkaline minerals).
   • For pathways that strip CO₂ gas from seawater and sequester the CO₂, risks of permanence of storage and potential for leakage
   • For pathways that remove dissolved inorganic carbon from seawater as calcium carbonate^[2]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 , impacts of large quantities of new calcium carbonate on diversity, abundance, and ecosystem function of marine environments

1. Risks Shared by Electrolysis and Electrodialysis
   • The potential for changes in water column particle concentrations, turbidity, and optical properties if precipitation (inorganic mineral formation) of carbonates occurs due to local increases in alkalinity and pH.  
   • Mortality of marine life through seawater intake pumps and filters
   • Shifts in phytoplankton, invertebrate and vertebrate physiology, competition and/or mortality due to decreases in acidity as CO₂ is removed and/or alkalinity is added^[1]Renforth, P., and G. Henderson (2017), Assessing ocean alkalinity for carbon sequestration, Rev. Geophys., 55, 636–674, doi:10.1002/2016RG000533. . For example, do the preceding seawater chemistry changes provide an increased competitive advantage for calcifiers over and above the restoration of calcifiers/calcification from ongoing ocean acidification?
   • Risks about permanence and impacts of elevated concentrations of bicarbonate in the oceans.
2. Risks Specific to Electrolysis
   • Chlorine gas production and handling
3. Risks Specific to Electrodialysis
   • Production of large quantities of acid via electrodialysis that must be safely consumed or neutralized (e.g., via reaction with alkaline minerals).
   • For pathways that strip CO₂ gas from seawater and sequester the CO₂, risks of permanence of storage and potential for leakage
   • For pathways that remove dissolved inorganic carbon from seawater as calcium carbonate^[2]Erika Callagon La Plante, Dante A. Simonetti, Jingbo Wang, Abdulaziz Al-Turki, Xin Chen, David Jassby, and Gaurav N. Sant ACS Sustainable Chemistry & Engineering 2021 9 (3), 1073-1089 DOI: 10.1021/acssuschemeng.0c08561 , impacts of large quantities of new calcium carbonate on diversity, abundance, and ecosystem function of marine environments

1. Risks Shared by Electrolysis and Electrodialysis
   • The potential for changes in water column particle concentrations, turbidity, and optical properties if precipitation (inorganic mineral formation) of carbonates occurs due to local increases in alkalinity and pH.  
   • Mortality of marine life through seawater intake pumps and filters
   • Shifts in phytoplankton, invertebrate and vertebrate physiology, competition and/or mortality due to decreases in acidity as CO₂ is removed and/or alkalinity is added. For example, do the preceding seawater chemistry changes provide an increased competitive advantage for calcifiers over and above the restoration of calcifiers/calcification from ongoing ocean acidification?
   • Risks about permanence and impacts of elevated concentrations of bicarbonate in the oceans.
2. Risks Specific to Electrolysis
   • Chlorine gas production and handling
3. Risks Specific to Electrodialysis
   • Production of large quantities of acid via electrodialysis that must be safely consumed or neutralized (e.g., via reaction with alkaline minerals).
   • For pathways that strip CO₂ gas from seawater and sequester the CO₂, risks of permanence of storage and potential for leakage
   • For pathways that remove dissolved inorganic carbon from seawater as calcium carbonate, impacts of large quantities of new calcium carbonate on diversity, abundance, and ecosystem function of marine environments

1. Localized reductions in ocean acidification, with expected benefit(s) to industries that rely on these localized improvements such as aquaculture and tourism
2. Creation of employment in industries producing carbon-negative byproducts from electrochemical CDR :
   • Electrolysis: hydrogen gas, chlorine gas, and oxygen gas, as well as hydrochloric acid
   • Electrodialysis: hydrochloric acid

1. Localized reductions in ocean acidification, with expected benefit(s) to industries that rely on these localized improvements such as aquaculture and tourism
2. Creation of employment in industries producing carbon-negative byproducts from electrochemical CDR {{2}:
   • Electrolysis: hydrogen gas, chlorine gas, and oxygen gas, as well as hydrochloric acid
   • Electrodialysis: hydrochloric acid

1. Need to populate this section