In direct air capture (DAC), we don’t have decades left to deliver climate impact — we need our technology to scale now. Yet, scientifically speaking, there are hundreds of different ways you can strip carbon from the air. In a race with so many horses and such high stakes, which one do you choose to develop?
At Mission Zero, we believe the answer lies in electrochemistry. Offering one of the lowest carbon footprints and highest energy efficiencies of all direct air capture methods, electrochemical direct air capture promises a truly scalable and affordable way to quickly remove CO₂ from the atmosphere.
Free from energy intensive heat requirements and able to run entirely on renewables, electric-only DAC pathways have demonstrated the potential to capture CO₂ with up to 95% sustained efficiency, while consuming less energy than conventional heat-based DAC processes.
Wonderfully, even within electrochemical direct air capture, there are lots of different technological pathways to choose from. To navigate the nuance, here’s a whistle-stop tour of electrochemical direct air capture — covering the main types of electrochemical DAC technology, what they each bring to the table, and how we decided on the technology that sits inside our first commercial DAC plants.
What is electrochemical direct air capture?
This heat-free and fully electrified process uses electrochemical reactions to recover CO₂ directly from the atmosphere. Unlike other DAC technologies, it does not rely on energy-intensive heat and pressure, or slower capture and release triggers such as humidity. Electrochemical direct air capture can work with 100% renewable power sources, requiring less space than the often complex mechanical systems used in ‘traditional’ DAC without compromising on performance.
Types of electrochemical direct air capture technology
Within the DAC community, there is an array of electrochemical carbon capture methods currently being explored as valuable additions to the planet’s climate mitigation toolkit. Here’s a brief overview of the main ways of doing electrochemical direct air capture.
Membrane Electrodialysis
At Mission Zero, we’ve pioneered a new membrane electrodialysis approach which efficiently recovers CO₂ from the air using a continuous capture and release loop.
How it works: Air is brought into contact with a reactive liquid solvent, which dissolves its carbon content. Electricity then selectively forces the carbon in that liquid through an electrodialysis stack and causes it to bubble out of the solution as pure CO₂. The carbon-depleted solvent is recycled by the system to repeat the process all over again.
Pros:
- Energy efficiency: Heat-free process uses less energy than most conventional approaches to DAC.
- High CO₂ selectivity: Can be tuned to selectively target CO₂ over other gases, enhancing capture efficiency in mixed gas streams like ambient air.
- Circular system: The solvent used to capture CO₂ from the air is recycled in a continuous loop, maximising resource efficiency and minimising human input.
- Technological maturity: Electrodialysis stacks are proven technology used widely across industry and supported by established global supply chains. This derisks the process for rapid commercial scale-up.
Cons:
- Chemical management: The use of chemicals in the process calls for considered waste management protocols.
Alkaline Electrolysis
How it works: An alkaline solution captures CO₂ before undergoing electrolysis (where an electric current drives a chemical reaction) to release the CO₂.
Pros:
- Hydrogen production: This process simultaneously produces hydrogen gas, which is valuable as a clean fuel or chemical feedstock.
- Mature technology: This is a well-established industrial process, making it more reliable and reducing risks and costs associated with its deployment at scale.
Cons:
- Byproduct management: Alkaline electrolysis is most commonly used for the production of hydrogen, meaning energy and resources must be invested in managing both gas streams, rather than focused solely on carbon capture.
- sharing energy and resources away from CO₂ capture and release to manage surplus gas.
- Energy intensive: Requires a significant amount of electrical energy, which can be costly and may reduce overall efficiency if not powered by renewable sources.
- Material corrosion: The alkaline environment can cause corrosion of hardware, necessitating the use of expensive, corrosion-resistant materials.
- Limited CO₂ capture: Unwanted side reactions, such as hydrogen or oxygen production, can occur which reduce the efficiency of CO₂ capture and complicate the process.
Electro-Swing Adsorption
How it works: Electricity attracts and binds CO₂ from the air onto an adsorbent material. When the electricity is turned off, the CO₂ is released and can be collected for use or storage, allowing for controlled capture and release cycles.
Pros:
- Precise capture and release: Offers highly controllable CO₂ capture and release cycles by applying and reversing an electric potential. This control allows for efficient and targeted CO₂ management.
- Energy efficient regeneration: Regenerates the adsorbent material with relatively low energy input.
- CO₂ selectivity: Can be tuned to selectively target CO₂ over other gases, enhancing capture efficiency in mixed gas streams like ambient air.
Cons:
- Operational and scaling complexity: The need to cycle between capture and release phases can add complexity to the operation and control systems.
- Degradation: The materials used to adsorb CO₂ may degrade over time with repeated cycling, leading to reduced efficiency and the need for frequent replacement or regeneration.
- Energy intensive: Releasing captured CO₂ can require significant energy input, particularly if high-purity CO₂ is required.
Cathodic Adsorption
How it works: Captures CO₂ from the air using a device similar to a battery or fuel cell. While CO₂ is being captured, the device can also generate electricity that can be used elsewhere, making it a dual-purpose system.
Pros:
- Direct CO₂ utilisation: Allows for the direct utilisation of captured CO₂ in electrochemical reactions, converting it directly into fuel or useful chemicals within one system.
- Energy recovery potential: Dual functionality of the system (generating electricity while capturing CO₂) can improve overall energy efficiency.
Cons:
- High cost of catalysts: Often requires the use of expensive catalysts, such as platinum or other noble metals, which can make the system costly to implement at scale.
- Degradation: Electrodes in fuel cells can degrade over time, especially under the harsh conditions of continuous operation, necessitating frequent maintenance or replacement of components.
- Lower selectivity for CO₂: Depending on the specific configuration, these systems may not be as selective for CO₂ capture as other methods, leading to lower overall capture efficiency or the need for additional steps.
Advantages of electrochemical direct air capture
Electrochemical DAC, specifically our method of membrane electrodialysis, has several advantages over more ‘traditional’ approaches to DAC.
Energy efficiency
Electrochemical direct air capture targets the CO₂ molecule directly, meaning that no energy is wasted on stimulating the capture medium — something which limits the energy efficiency of other DAC pathways. EDAC technology can also operate at room temperature, eliminating the need for the higher, energy-draining temperatures and pressures that many other forms of DAC depend on.
Sustainability
Electrochemical carbon capture can take place with minimal resources. As a fully electrified pathway that can handle the load fluctuations of intermittent supply, it can also run entirely off clean renewable energy. This is in stark contrast to many heat-based forms of DAC which are dependent on fossil sources of energy. This is especially important for carbon removal developers seeking DAC CO₂ with the lowest possible carbon intensity, as it produces a higher quality carbon removal credit. It is also good news for the build-out of renewable energy, as co-locating an electrochemical DAC system with renewable assets can create a valuable use case for curtailed energy that would otherwise go unused. Electrochemical DAC typically requires a smaller land footprint than other approaches to carbon removal, avoiding conflict with agricultural and ecological needs.
Flexibility
Electrochemical CO₂ capture is unique in that production can be flexibly ramped up and down in seconds, allowing the system to be fine tuned to the energy profile of any given location. This enables continual cost optimisation of the system, increasing the recovery of CO₂ when renewable energy is at its cheapest and most abundant, and driving it down during peaks in demand. This energy flexibility is baked into our technology and doesn’t apply to other, more ‘traditional’ methods of direct air capture.
Productivity
Unlike many forms of direct air capture, the capture and regeneration cycles of electrochemical technology are decoupled — meaning they can both be run continuously and independently of one another. This offers huge productivity gains compared to batch-based DAC processes and also allows maintenance to be performed on one process without bringing the other to a standstill, maximising for system uptime.
Scalability
Thanks to our three first-of-a-kind DAC deployments, we’ve been able to refine our electrodialysis process to drive ongoing improvements in our carbon capture and release loops. Our research and development team is working hard to ensure that our DAC units can be easily upgraded with each evolution of our climate tech, minimising redundancies. Our specific electrodialysis process also leverages mature industrial components supported by established supply chains, shortening the time between lab testing and the real-world deployment of our direct air capture technology.
Why we think electrochemical DAC is a winner
Electrochemical direct air capture eliminates many of the challenges faced by ‘traditional’ carbon removal technologies, addressing concerns around the need for large amounts of energy and the resulting possibility of a harbouring reliance on fossil fuels.
Although electrochemical carbon removal can come in many different forms, each with its own merits and limitations, for us membrane electrodialysis is able to offer the best balance of efficiency, scalability, and long-term viability. We ultimately chose to develop electrochemical direct air capture technology because it:
- Can run 100% off renewables and has the potential to be one of the most energy efficient DAC pathways going;
- Offers incredible flexibility to deliver cost-optimal performance in any given location;
- Can quickly scale using existing technologies to achieve technical and manufacturing maturity extremely quickly;
- Is simple enough at a systems level to allow for easy integration and modular upgrading;
All of which produce a powerful, multi-purpose tool for delivering high-quality carbon removal and industrial decarbonisation.
Dive deeper: How energy flexibility benefits cost in electrochemical direct air capture
