Verdox ($100M for electric carbon removal)

Verdox, an American startup founded in 2019, specializes in the capture and removal of carbon dioxide (CO₂) from various sources, including the air and emission sources such as aluminum production. Verdox’s technology is radically distinct from existing carbon removal solutions because it does not rely heavily on heat. Instead, it uses electrochemistry to control the capture and release of CO₂. The high energy efficiency and scalability of Verdox’s technology have the potential to contribute significantly to the carbon removal challenge. The company aims to make carbon capture and removal scalable and cost-effective. Verdox was selected as one of the top 15 teams to receive a $1M Milestone Prize in the XPRIZE Carbon Removal competition.

Challenges: carbon emissions and Direct Air Capture

Carbon emissions

In this urgent, authoritative book How to Avoid a Climate Disaster, Bill Gates sets out a wide-ranging, practical—and accessible—plan for how the world can get to zero greenhouse gas emissions in time to avoid a climate catastrophe. (see on Amazon)

Since the early 1900s, carbon dioxide (CO₂) levels in the atmosphere have increased by 50% due to human activities. When fossil fuels (such as coal, oil, and natural gas) are burned for energy production, transportation, and industrial processes, CO₂ is released into the atmosphere. This excess CO₂ acts as a greenhouse gas, trapping heat and causing the air and ocean temperatures to rise. CO₂ emissions play a crucial role in driving climate change.

This warming effect has caused the global average temperature to rise by about 1.1 ºC since the pre-industrial period. This has led to rising in the frequency and intensity of extreme weather events, melting of polar ice caps and glaciers and rising sea levels, shifts in species ranges and increased risk of species extinction, agriculture and food security, and ocean acidification.

To mitigate these impacts, the Paris Agreement aims to limit global warming to well below 2 ºC above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) estimates that a “carbon budget” of about 500 GtCO₂, which corresponds to about ten years at current emission rates, provides a 66% chance of limiting global warming to 1.5 ºC.

Direct Air Capture

Direct Air Capture (DAC) is a process that extracts CO₂ directly from the atmosphere, as opposed to industrial emissions with a high CO₂ content. The captured CO₂ can then be either permanently stored in deep geological formations, thereby achieving CO₂ removal (CDR), or used as a climate-neutral feedstock for a range of products that require a source of carbon.

The basic principle of DAC involves using large-scale machines or facilities equipped with specialized filters or sorbents which are designed to attract and bind with CO₂ molecules from the air while allowing other gasses, such as nitrogen and oxygen, to pass through. After the CO₂ is captured, it is separated from the sorbent through a regeneration process, resulting in the release of CO₂.

DAC technology employs a variety of methods, but chemical sorbents or solvents are typically used to capture CO₂. These sorbents can chemically react with CO₂ to form solid compounds or dissolve the CO₂ in a solvent. The captured CO₂ is then released from the sorbent or solvent via heating or other processes, allowing for its storage or utilization.

Direct air capture technology challenges

DAC plays an important and growing role in net-zero pathways. Capturing CO₂ directly from the air and permanently storing it removes the CO₂ from the atmosphere, providing a way to balance emissions that are difficult to avoid, including from long-distance transport and heavy industry. DAC has seen a surge in interest and investment over the past few years, and a growing number of companies are entering the market due to the realization that carbon removal will increasingly be needed to meet national and global climate goals, as well as the advantages of DAC relative to other carbon removal technologies.

However, this technology is still in its infancy and faces several challenges that are stunting its global adoption and deployment.

One of the main challenges is that CO₂ is present in the air at a much lower concentration than other commonly targeted sources, such as flue gasses resulting from energy generation and industrial processes. This makes it technically challenging and requires a lot of energy.

As carbon dioxide removal from ambient air is an energy-intensive process, DAC technology is more expensive per ton of CO₂ removed than many mitigation strategies and natural climate solutions. Today, the price range for DAC ranges between $250 and $600. By the end of this decade, however, the cost of DAC technology is projected to fall to $250-$300/mtCO₂e (million tons of CO₂ equivalent) for a multi-megaton capacity range. If further industrialization is accomplished within the ecosystem of this emerging industry, prices may fall to between $100 and $200/t.

The sociopolitical acceptance of DAC is also a challenge. Currently, there is no established market for carbon removal, and the demand for carbon removal is not yet sufficient to support the large-scale deployment of DAC. Some advocates worry the carbon capture process may not be scaled up fast enough to make an impact. However, the demand for carbon removal is expected to increase as more countries and companies set net-zero targets and seek to offset their emissions. In addition, governments and other stakeholders must provide substantial funding and support.

The book Carbon Capture, written by Herzog, a pioneer in carbon capture research, begins by discussing the fundamentals of climate change and how carbon capture can be one of the solutions. (see on Amazon)

Direct air capture companies

Several companies, such as Carbon Engineering, Climeworks, Heirloom, Noya, Mission Zero, Carbyon, and Sustaera, are developing DAC technologies.

Carbon Engineering DAC technology is an engineered mechanical system that extracts CO₂ from the air using a combination of fans, filters, and chemical reactions. The captured CO₂ is then compressed and stored underground or reused. Carbon Engineering’s DAC technology is capable of capturing millions of tons of CO₂ annually, and individual DAC facilities can be built to capture one million tons of CO₂ annually.

Climeworks specializes in DAC technology that extracts CO₂ from the air using a solid sorbent. The captured CO₂ is then released through a regeneration process, while the sorbent material is reused. Climeworks has developed several DAC plants worldwide and is working to scale up its technology to capture millions of tons of CO₂ annually. The company operates the largest operating DAC plant, Orca, in the world. The plant is located in Iceland and is capable of drawing down the volume of carbon dioxide emissions equivalent to approximately 870 cars annually.

Heirloom uses limestone (CaCO₃) instead of synthetic sorbents to capture CO₂ from the air and store it safely and permanently. Limestone is heated in renewable-energy powered calciners to remove CO₂ and produce Ca(OH)₂ sorbents from the hydration of CaO powders. Ca(OH)₂ sorbents are placed on vertically stacked trays, and algorithms are used to optimize their capacity to absorb CO₂ in different environmental conditions. Heirloom’s DAC technology accelerates the natural property of limestone, reducing the time it takes to absorb CO₂ from years to just three days. The company claims that its technology has the lowest peer-reviewed, at-scale cost of any direct air capture technology on the market.

Noya has developed a unique DAC technology that combines the existing pieces of industrial cooling towers with solid CO₂ sorbents. This transforms industrial cooling towers into CO₂ capture machines, which radically reduces the upfront capital costs and installation time required to perform direct air capture. Therefore, Noya’s approach to DAC will enable them to scale quickly and provide low-priced carbon removal in the near-term.

Mission Zero has developed a DAC technology that continuously captures CO₂ from the air with low energy consumption. Mission Zero uses a well-established electrodialysis technology to capture CO₂ from the air and turns CO₂ into carbonic acid (H₂CO₃), which dissociates into HCO₃⁻ and proton (H⁺). The H₂CO₃ solution is circulated through an electrodialysis cell, which separates HCO₃⁻ from the absorbent solution by passing it through an anion-exchange membrane into a second absorbent solution, where HCO₃⁻ anions recombine with protons in the second absorbent solution to form carbonic acid, which readily decomposes into CO₂ in the release vessel where CO₂ is collected and stored.

Carbyon develops a fast swing process by means of a continuously rotating drum to realize a low-cost, energy-efficient DAC technology. The rotating drum comprises activated carbon fiber membranes. The surface of fibers are functionalized with a monolayer of amines that are used as CO₂ adsorbents. Such a thin surface sorbent allows a rapid CO₂ absorption at ambient temperature and fast regeneration below 100 ºC. Thereby, one cycle of absorption and regeneration occurs in less than 5 seconds. The fast swing CO₂ capture process is the key to lower the energy consumption as well as the cost of the machine.

Sustaera has developed monolithic structured material assemblies that use renewable electricity to remove CO₂ directly from the air. The monolithic structured material assembly has a monolithic substrate with a honeycomb-like structure positioned between two mesh electrodes. The monolithic substrate’s channel walls are coated with layers of conductive carbon desorption and sodium carbonate (Na₂CO₃) sorbent. The Na₂CO₃ sorbent absorbs CO₂ from the airflow within the channels until they become saturated. To regenerate sorbent, the conductive carbon desorption layer receives renewable electricity input and in-situ heats the sorbent layer to quickly liberate CO₂ at temperatures below 120 ºC in a few minutes.

Verdox Technology

Verdox has developed electroswing adsorption cells with patterned electrodes that contain quinone materials to capture CO₂ from air and emission sources like aluminum production. The patterned electrode comprises conductive carbon scaffold which is coated with electroactive quinone materials and extends into a polymer gel electrolyte to capture and liberate CO₂ by applying a current at select voltages in ambient temperature. The patterned electrode has multiple gas regions that facilitate the diffusion of CO₂ to quinones. Verdox’s electrochemical carbon removal technology offers a more energy-efficient approach to capturing CO₂ compared to traditional carbon capture technologies. The latter often require large amounts of heat and have inherent inefficiencies.

Verdox carbon removal technology

The diagram below depicts Verdox’s electroswing adsorption system for CO₂ capture.

Verdox electroswing adsorption system for CO₂ capture (Source Verdox).

The system has two sets of electroswing adsorption cells. Each set comprises a stack of electroswing adsorption cells. As depicted in the diagram below, a gas mixture flows through channels that separates each pair of neighboring cells.

Stack of Verdox electroswing adsorption cells (ref. US20210387139A1).

Both sets operate in parallel in an alternating fashion, with one set operating in a charge mode and capturing CO₂ from a gas mixture and the other set operating in a discharge mode and releasing CO₂. The system allows for continuous CO₂ capture and removal.

The system also includes separate housings for each of the sets of electroswing adsorption cells. Additionally, the system has conduits and valves arranged to direct flow in a specific manner.

The system is modular and scalable. Depending on the application, additional sets of electroswing adsorption cells can be added in parallel or in series.

Verdox electroswing adsorption cell

The diagram below depicts an electroswing adsorption cell in detail. An electroswing adsorption cell has two patterned electrodes (working electrodes) placed on both sides of a counter electrode. The working electrode and counter electrode are electrically separated by a porous separator.

Patterned electrodes

The patterned electrodes comprises gas regions, a conductive scaffold, electroactive quinones, and a gel polymer electrolyte.

The patterned electrode incorporates gas regions to facilitate the diffusion of gas into and out of the electrode material during CO₂ capture and release.

The conductive scaffold comprises large carbon fibers that are coated with carbon nanotubes or carbon nanofibers. Such a structure has a large surface area that can be coated with a substantial quantity of electroactive quinone materials to increase CO₂ capture efficiency. The quinone-coated conductive scaffold extends into a gel polymer electrolyte. Therefore, the porous, electronically conductive scaffold with a high surface provides a large interfacial contact area between quinones and the electrolyte.

How are patterned electrodes fabricated?

A slurry is formed by mixing the crosslinkable polymer electrolyte and the quinone-coated conductive scaffold. The slurry is coated onto a separator to produce a composite film of several hundreds micrometers in thickness. In the composite film, polymers with cross linkable groups are cross linked triggered by heat, radiation, or a chemical trigger. Using laser ablation, lithography, mechanical impression, machining, or etching, a portion of the composite film is removed to form the plurality of electrolyte regions.

Quinones

A quinone can be reduced to radical anion or dianion. The chemical processes are reversible, as shown in the diagram below.

In the patterned electrode, quinone materials are coated on the surface of the porous conductive scaffold. They become radical anions or dianions that react with CO₂ when they are reduced. Each quinone can bind with up to two CO₂ molecules. Reversing the current regenerates the quinone and releases the CO₂.

Verdox has developed stable and effective CO₂ capture quinones materials. The quinone cores are bonded with a cationic group and/or a hydrogen bond donor. These quinone materials can kinetically and thermodynamically favor the reaction between the CO₂ and the radical anions or dianions of quinones. Below are the chemical structures of several quinones.

Quinone materials in Verdox electroswing adsorption cells for CO2 capture (ref. US20230012689A1) — Quinone materials in Verdox electroswing adsorption cells for CO₂ capture (ref. US20230012689A1).

Stabilizing additives can also be added into the conductive scaffold composite to facilitate the reaction between the reduced quinones and the CO₂. Among these additives are metal cations like lithium ion and hydrogen-bond donors like phenol (see US20220339579A1).

Electrolyte

The electrolyte can be gel polymer electrolyte, which comprises a polymer matrix with a high affinity for the electrolyte contained within the polymer matrix.

The polymer matrix comprises a polymer with functional groups that are capable of forming cross links in response to heat, radiation, or a chemical trigger. A room temperature ionic liquid (RTIL) is maintained in the polymer matrix by capillary action or wetting of the polymer matrix and conductive scaffold with the ionic liquid.

An example of the polymer gel electrolyte comprises poly(ethylene glycol) diacrylate (PEGDA) as gel-former to immobilize the bis(trifluoromethylsulfonyl)imide (BMIM-TFSI) ionic liquid.

Counter electrode

The counter electrode comprises a complementary electroactive composite layer deposited on both sides of a conductive substrate, such as carbon paper. The complementary electroactive materials can be an electroactive inorganic complex, such as an alkali metal-transition metal oxide, or a metallocene such as ferrocene or polyvinyl ferrocene.

Separator

The separator is positioned between the patterned electrode and counter electrode. The separator prevents a short-circuit.

The separator is porous polymer or polymer/inorganic composite materials, such as polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-alumina composite, or a microporous olefin, such as a microporous polyethylene or microporous polypropylene.

How does Verdox technology work?

During operation, a potential difference is applied to the electroswing adsorption cells during a time so that a gas mixture is exposed to the quinones.

During a charge (capture) mode, quinones are reduced and bind to up two CO₂ via the following chemical reactions:

Quinone molecule captures and releases CO2 via redox reactions. — Quinone molecule captures and releases CO₂ via redox reactions.

In this manner, CO₂ can be removed from the gas mixture to produce a treated gas mixture with a less amount of the CO₂ than the original gas mixture.

After the completion of capture mode, a vacuum is applied to the electroswing adsorption cells to remove any remaining gas.

During the discharge (release) mode, a reverse current is applied to the electroswing adsorption cells. Quinones are oxidized to release CO₂. During or after the discharge mode, a vacuum condition is applied to the electroswing adsorption cells to remove the released CO₂.

Verdox Patent

US20210387139A1 Electroswing adsorption cell with patterned electrodes for separation of gas components
US20220145002A1 Quinone-containing poly(arylene), methods for the manufacture thereof, and use for electrochemical gas separation
WO2022104000A1 Composite for electrochemical gas separation
US20230012689A1 Electroactive species and method for electrochemical gas separation
US20220339579A1 Method for electrochemical gas separation

Verdox Products

Carbon offset credit market

The market value of carbon offset credits varies widely. In current carbon markets, the price of one carbon credit can range from a few cents per metric ton of CO₂ emissions to $15/mtCO₂e (metric tons of CO₂ equivalent) or even $20/mtCO₂e. However, the voluntary carbon offset market, which was worth about $2 billion in 2021, is projected to grow to $10-40 billion by 2030, transacting 0.5-1.5 billion tons of CO₂ equivalent, as opposed to the current 500 million tons. The total value of carbon credits produced and sold to help companies and individuals meet their de-carbonization goals could approach $1 trillion as soon as 2037.

Verdox product

Verdox’s technology is still in the development and commercialization phase, with the company working on its first announced commercial client, Norwegian aluminum company Hydro. As the technology continues to be refined and scaled up, its efficiency and performance compared to other carbon capture methods will become clearer.