Absorption and Electrochemical Regeneration

Capture Mechanism

Liquid

Furthest Progress*

TRL 6

Highest Risks

Energy
Cost
Water
Environment

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Method Overview

Definition:

CO2 absorption with an alkaline solvent (where CO2 is dissolved or diffused in a liquid to form a solution) followed by CO2 release and solvent regeneration in an electrochemical cell where a change in voltage is used to separate CO2 from the solvent.*

Example:

Fans pull air over potassium hydroxide that chemically binds with CO2 in air and forms potassium carbonate. The carbonate is electrochemically processed to release concentrated CO2 for storage and regenerate the hydroxide solution.*

Advantages:

Electrochemical DAC methods can be more energy efficient than other methods, as they apply electrical energy to CO2 capture and release directly. By contrast, DAC methods that utilize thermal energy for regeneration commonly waste energy by heating entire reactors, rather than just the sorbent materials.
Electrochemical DAC can easily integrate with renewable energy sources.
Liquid electrochemical DAC approaches are based on well-developed technologies used in other industries like water purification (electrodialysis) and H2 production (alkaline electrolysis).
Electrochemical DAC is modular. This approach benefits from simplified designs, relative to temperature swing-based DAC, that accomidate various environmental conditions, leading to greater standardization and mass production.
Electrolysis-based DAC approaches co-produce H2 as a potentially green fuel and feedstock that, along with CO2, is used to synthesize other commodity chemicals like fuels.

Disadvantages:

Electrolysis requires a high minimum energy and high voltage. These conditions are needed to sustain the water splitting reactions that produce hydroxide ions to capture CO2 and create a large pH gradient to release it.
The acidic environment created at the anode requires chemically resistant materials to ensure stability and performance.
CO2 release in electrolysis-based systems is accompanied by O2 generation, requiring additional purification downstream.
Electrodialysis requires lower voltage than electrolysis but relies on expensive polymer membranes engineered to dissociate water into charged ions and transport them selectively.
Electrodialysis cells can have high internal resistance, causing large ohmic losses and poor ion conductivity that increase energy demand and lower CO2 capture efficiency.

* Reproduced from The Applied Innovation Roadmap for CDR (2023) by RMI.

Company Overview

Plot of estimated funding vs. deployment status of companies utilizing this approach. Select data points to view company details. Only companies for which funding information is publicly available are included. Companies without funding information are tabulated with related details where relevant.

Summary of Deployments

View DAC deployments within this approach that have achieved or surpassed prototype scale. Planned deployments are included. Sort DAC deployments by company, scale, start of operations, and more. Because DAC is a rapidly evolving industry, this list may not be exhaustive.*

* Due to uncertain funding, plans for most DOE-funded DAC Hubs are not included in this analysis.

Risk Assessment

RMI's Applied Innovation Roadmap for CDR (2023) categorizes the risks associated with different classes of DAC technologies. Their assessment of this method is reproduced here and contextualized with current self-reported company data, where available.

Energy Requirements

High risk: Electrochemical solvent regeneration is very energy intensive.

Energy needs meet our DAC criteria for “high risk” (>5 GJ/tCO2). Capture and solvent regeneration require approximately 7.8 GJ/tCO₂, but can be lower depending on the process variant. The full DAC+S pathway will require additional energy (e.g., compression, transport, and storage).

Self-reported energy requirements of DAC companies (GJ/tCO2). Electrolysis: Phlair: 5.0 (with H2 recycling). Electrodialysis: Mission Zero: 7.8, Ucaneo: 5.4, Yama: 4.5 (with thermal input)

Material Requirements

Medium risk: High-demand materials are required.

Apart from basic construction materials (e.g., steel, cement), this solution requires solvents, high-demand materials for electrodes, and membranes that need to be synthesized and / or purchased.

Cost Requirements

High risk: Technology is modular across certain components with cost estimates >$500/tCO2.

Rating is based on the cost estimates for FOAK plants and the data quality used for these estimates. Different cut-offs for modular/non-modular technologies were applied, as modular approaches are comparatively cheaper and easier to scale. This technology meets our criteria for “high risk” (FOAK: >10 ktCO2; >$500/tCO2 plus available plant data).

Land Requirements

Low risk: Significant land areas are suitable for DAC siting.

The DAC plant is expected to have minimal footprint per capture capacity compared to other CDR solutions and can be deployed on most types of land. The footprint is expected to be larger if land for energy production is considered.

Water Requirements

High risk: Large volumes of water are evaporated when operating the facility.

This DAC technology, specifically electrolysis, requires large amounts of water. The magnitude is unknown but is expected to be comparable to other liquid solvent technologies, especially "Absorption and High-Grade Heat Regeneration", i.e. ~5 GtH₂O/GtCO₂.

Self-reported water requirements of DAC companies (GtH₂O/GtCO₂). Electrolysis: Phlair: 8.2. Electrodialysis: Mission Zero: 0.1.

Environmental Impact

High risk: No / incomplete data available.

Apart from impacts associated with energy, water, and material requirements, including sourcing high-demand materials for the electrodes, no other impacts are anticipated. However, no LCA study is currently available for this solution.

Co-Location of DAC and Storage

Low risk: Co-location of DAC and storage is relatively easy.

The DAC unit should not be situated in hot and dry environments due to high water requirements. However, there is sufficient geological storage in water-rich areas that co-location should not be a problem.

Secure Storage for 100+ Years

Low risk: Storage is durable.

Geological sequestration or in-situ mineralization (primary storage options) are considered permanent storage approaches.

Path to MRV at Scale

Low risk: Measurement to inform MRV is straightforward.

DAC+S measurement and monitoring is straightforward. Capture occurs in a controlled environment and geological injection has established monitoring standards.

Key Innovations

Electrochemical DAC methods emphasize the importance of energy efficiency and seamless integration with renewables. While waste heat sources are generally incompatible and electricity must be used almost exclusively, electrochemical DAC can offer greater energy efficiency than thermal methods by applying energy to CO2 capture and release steps directly, rather than heating entire reactors. While this DAC approach avoids these inefficiencies it still currently requires, on average, comparable energy requirements as thermal methods because of high voltage requirements (electrolysis) and high internal resistance (electrodialysis). In addition, electricity must be provided by low-carbon sources to deliver effective CDR. Similarly, its cost remains high due to energy consumption and costly materials like ion-exchange membranes.

The technical readiness of this method is lower than most thermal approaches so its future prospects are encouraging if its energy efficiency can be improved, especially as the cost and availablity of renewable energy are expected to improve in the next decade. To sieze this advantage, companies are innovating in Material, Process, and Equipment design.

Material Design:

Membranes – Bipolar membrane electrodialysis (BPMED) relies on stacks of specialized polymer membranes engineered to dissociate water into charged ions and transport them selectively. Balancing high membrane costs against performance (durability, efficiency, etc.) is likely the greatest current limitation of this method and should be supported by R&D. While electrolysis (EL) requires much less membrane area to capture an equivalent amount of CO2, it faces other tradeoffs, such as greater energy consumption and higher voltage requirements.

Process Design:

Intermittent Renewables - Most companies pursuing this DAC method utilize electricity as their sole energy input, so they must be capable of effective integration with low-carbon energy sources like wind and solar that are naturally intermittent. Ensuring durable high-performance CO2 capture despite interruptions and grid fluctuations, and maintaining continuous operation while using intermittent energy are important focuses of process design.
Energy Savings - Some companies have described ways in which their process design lowers energy consumption or includes on-board energy generation. Others have optimized their process design to integrate with other industries like water treatment and synthetic fuel production.

Equipment Design:

Contactor Design - DAC requires flowing enormous volumes of air through a contactor unit to capture CO₂ and that can come at a high energy penalty, especially due to pressure drop across the contactor. Innovations in contactor design, such as using passive air contactors, seek to lower the energy required to filter CO2 from air.
Cell Design - While BPMED and alkaline electrolysis equipment is well-developed in other applications like water desalination and H2 fuel production, respectively, optimizing this equipment for DAC – for example, recycling co-produced H2 to lower the voltage requirements of electrolysis – can significantly improve performance.

This tool organizes several key characteristics of DAC companies for which public information is available based on these three categories. Search below by company name or search "Material", "Process", of "Equipment" to view all related company activities.