What is it?
Ocean electrochemical systems pass an electrical current through seawater to drive chemical reactions that redistribute major ions, creating separate acidic and basic solutions that can be used for CO₂
removal in different ways. One common method uses an acidic solution to lower the pH of seawater. This shifts the chemical balance in the carbonate system toward dissolved CO₂,
which then degasses from the water and can be captured for long-term storage in underground geologic reservoirs. Another variation uses the basic solution to increase the alkalinity of seawater, which shifts the carbonate system so that the ocean can absorb and remove more atmospheric CO₂,
similar to Deploy Ocean Alkalinity Enhancement. Several other variations exist, including designs that use the acidic stream to weather alkaline rocks and the basic stream to precipitate carbon-containing minerals, such as carbonates. These systems can operate as closed systems, in which carbon removal is achieved with on-site infrastructure, as open systems, which rely on effluent discharge into the ocean to complete carbon removal, or as combination hybrid systems that combine both approaches.
Does it work?
The fundamental chemistry and physics underlying electrochemical methods for shifting chemical reactions and ionic balances in solutions are well understood and sound. These approaches are already used on a large scale in industrial applications, such as the chlor-alkali process for producing sodium hydroxide and chlorine. However, using electrochemistry to remove CO₂
from seawater remains in early development. Studies show that CO₂
can be removed using these methods, and some pilot projects are currently underway; however, the effectiveness and costs of approaches, particularly when energy requirements are factored in, are still uncertain. In addition, the effectiveness of ocean electrochemistry for CO₂
removal also depends on how the removed CO₂
is stored. For example, to have a beneficial climate impact, CO₂
degassed from acidified seawater must be permanently stored deep underground rather than used as a chemical precursor for the manufacture of other products or for enhanced oil recovery, both of which create additional GHG emissions.
Why are we excited?
Ocean electrochemical systems for CO₂
removal offer several potential advantages, including useful co-products, opportunities to leverage existing infrastructure, and possible environmental benefits. Some electrochemical variations generate beneficial co-products, such as hydrogen gas, which could help offset costs and displace external fossil fuel energy demand. Some designs can also be coupled with existing brine streams in desalination or industry to leverage both infrastructure and waste feedstocks. In other cases, seawater itself serves as an abundant natural feedstock for these electrochemical processes. In some variants, environmental benefits may include local reductions in ocean acidification, which may benefit some marine organisms. Additionally, monitoring and verification of electrochemical variations using closed-system approaches may be more straightforward compared to other marine carbon dioxide removal (mCDR) approaches that require tracking carbon across large regions and depths of the ocean.
Why are we concerned?
Ocean electrochemical approaches for carbon removal present several challenges with respect to cost, effectiveness, and potential environmental impacts. Many designs are energy-intensive, require substantial infrastructure, and need large volumes of seawater. Their effectiveness and overall climate impact will depend on access to low-carbon electricity and accurate accounting of full life cycle energy use, since use of fossil-based electricity could offset much of the CO₂
removal benefits. Costs are unclear but are largely estimated to be well above US$500/t CO₂
for many variations. Additionally, some approaches, such as those that aim for carbonate mineral precipitation, do not inherently yield net CO₂
removal unless the alkalinity used for mineral formation is replenished, which can be costly.
If the electrochemical approach relies on capturing CO₂
from seawater, geologic storage will be required to dispose of the degassed CO₂.
Furthermore, some co-products of electrochemical approaches, such as acidic brines or chlorine gas, could exceed viable market demand at large scales and may require waste disposal or the development of technologies to reduce or eliminate their production. Finally, for open-system electrochemistry variants that rely on effluent interactions in the ocean to complete carbon removal, carbon accounting will likely need to extend far beyond the facility itself, making monitoring and verification of carbon removal similarly complex to other marine carbon dioxide removal approaches.
Environmental impacts are not well understood but will depend on the specific electrochemical approach. Approaches that discharge chemically altered effluent into the ocean could impact marine organisms near discharge points, with ecosystem responses that remain highly uncertain. Large-scale pumping of seawater could affect marine organisms through entrainment and other intake impacts, due to the large volume of influent needed for these approaches at scale. When these approaches require alkaline rocks, they raise concerns about the potential effects of mining, similar to Deploy Ocean Alkalinity Enhancement and Enhanced Rock Weathering.