Adsorption and Electrochemical Regeneration

Capture Mechanism

Solid

Furthest Progress*

TRL 6

Highest Risks

Energy
Cost
Environment

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Method Overview

Definition:

CO2 adsorption onto a solid sorbent (where CO2 is captured on the surface of a solid material), followed by CO2 release and sorbent regeneration in an electrochemical cell in which a voltage change is used to separate the CO2 from the sorbent.*

Example:

1) Ambient air is channeled through a stack of electrodes in which CO2 is adsorbed, then a voltage is applied through the stack to release concentrated CO2 for storage; 2) electrochemically reduced organic solids like quinones are used to chemically bind with CO2 from air and electrochemically oxidized to release CO2 for storage.*

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.
Lower estimated cost requirements due to reduced energy consumption, as well as the avoidance of costly materials such as ion-exchange membranes.
Simple modular system that avoids the need for flowing electrolytes/CO2-absorbent solutions. Scaling is simple and involves stacking multiple electrochemical cells.

Disadvantages:

The technology underpinning this approach is less developed than other electrochemical or DAC methods.
Oxidative instability commonly affects materials in this approach leading to chemical degradation and CO2 capacity loss when capturing CO2 in the presence of O2 (i.e., under ambient conditions).
Coupled CO2 capture and release steps as well as significantly varied CO2 concentrations between these steps can hinder the continuous operation of these systems. Continuous operation is possible with additional cells.
Slower CO2 capture kinetics, relative to liquid electrochemical approaches.

* 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: High energy requirements for sorbent regeneration are expected.

High energy requirements for electrochemical CO2 release are expected. Although lower energy values have been reported (~1 GJ/tCO₂), we classify this approach as high risk as limited data is currently available for a more rigorous assessment. DAC+S will also require additional energy (e.g., compression, transport, and storage), which is not included in the publicly available energy data.

Self-reported energy requirements of DAC companies (GJ/tCO2): Verdox: 1.5.

Material Requirements

Medium risk: High-demand materials are required.

Apart from basic construction materials (e.g., steel, cement), this solution requires chemicals (e.g., quinones) that need to be synthesized or purchased (for scalability, supply chains need to be in place) and high-demand materials for electrodes.

Cost Requirements

Very high risk: Not enough reliable data is available to assign a lower rating.

FOAK plants are expected at <10 ktCO2; process data is limited and no data on cost is available; net FOAK capture cost is expected to be very high risk at >$600/tCO2 (excluding compression, transport, and storage).

Land Requirements

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

These DAC plants are expected to have minimal footprint per capture capacity compared to other CDR solutions and can be deployed on most types of land. However, there is no public data regarding land requirements for this approach. The footprint is expected to be larger if land for energy production is considered.

Water Requirements

Low risk: No water is required.

Water is not used in this process and therefore it is not expected to be a risk.

Environmental Impact

High risk: No/incomplete LCA data available.

No LCA is currently available. However, apart from the impacts associated with energy, water, and material requirements, minimal to no other impacts are anticipated.

Co-Location of DAC and Storage

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

The DAC unit performance may be affected by different climate conditions. However, easy co-location with storage can be achieved due to the high CO2 purities from the DAC unit.

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 comparatively straightforward.

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

Key Innovations

Solid electrochemical DAC methods such as electro-swing adsorption and supercapacitive swing adsorption offer similar benefits as related liquid-based methods; by using only electricity for precise CO2 capture and release, this approach promises higher energy efficiency than heat-based systems. Solid electrochemical DAC approaches are distinguished from liquid-based systems by their use of reversible redox chemistry, which has the potential to lower energy consumption, especially compared to electrolysis. Solid electrochemical systems also avoid the costly membrane requirements of electrodialysis and are generally simpler, more modular systems.

Nonetheless, the technical readiness of this approach is low and companies are advancing Material, Process, and Equipment design to capture the benefits of this DAC approach.

Material Design:

Stability - Sorbent materials are reduced in redox-mediated electrochemical DAC to facilitate CO2 adsorption. However, in this state, the active materials (e.g., reduced polymeric quinones) are often highly susceptible to degratation by reacting with O2 instead. Improving the oxidative stability is a key focus to make this method viable.
Conductivity - Ongoing work is also focused on addressing the low electrical conductivity of many sorbent material active species. Conductive additives like carbon nanotubes are frequently mixed with active materials to achieve the necessary conductivity to capture CO2.

Process Design:

Alternative Processes - Most companies in this area are pursuing electro-swing adsorption, however, a small number are developing alternative processes such as supercapacitive swing adsorption (Norma) and direct utilization methods (Carbon Energy).
Energy Production - Some companies are integrating energy production, including renewable electricity and H2, into their processes.

Equipment Design:

Air Contactor - 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. In this approach, contactors must also support the electrochemical activity of the sorbent including by being sufficiently conductive.

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.