Researchers in the United States have increased the performance of electrochemical direct air capture of carbon dioxide by nearly an order of magnitude. Scientists from Johns Hopkins University and the TotalEnergies Research Center achieved this by fundamentally redesigning the technology. Instead of relying on large volumes of alkaline solution, they enabled carbon dioxide to react with alkali directly at the air-liquid interface. The new system operated continuously and stably for more than 50 hours.
Direct air capture (DAC) is widely regarded as one of the most promising technologies for mitigating climate change. However, implementing it remains extremely challenging because atmospheric air contains only about 400 CO₂ molecules per million air molecules. As a result, existing systems must process enormous volumes of air. Most current DAC technologies spray alkaline solutions inside large air contactors, but only a small fraction of the alkali actually reacts with CO₂. Consequently, large amounts of liquid must be circulated and significant amounts of energy are required to regenerate the absorbent.
The American researchers proposed a fundamentally different approach. Instead of feeding a pre-prepared alkaline solution into the system, they generated hydroxide ions directly inside an electrochemical cell. When an electric current is applied, oxygen from the air is reduced at a gas-diffusion electrode, producing hydroxide ions that almost instantly capture carbon dioxide molecules. This eliminates the slowest step of the conventional process – the dissolution of CO₂ into a large volume of liquid.
The key component of the new system is a porous, ion-conducting spacer made of an anion-exchange resin, positioned between the electrode and the membrane. It functions as a miniature three-dimensional reactor: hydroxide ions travel through its solid framework, while carbon dioxide diffuses freely through its pores. This architecture greatly increases the contact area between the reactants and extends their interaction time, allowing virtually all of the generated alkali to react with CO₂. To further improve efficiency, the researchers replaced continuous current operation with short electrical pulses. During the intervals between pulses, carbon dioxide has sufficient time to penetrate deeper into the porous structure and react completely with the hydroxide ions.
Another major challenge was to release the captured carbon dioxide in concentrated form. To accomplish this, the researchers employed AQDS (sodium anthraquinone-2,7-disulfonate), an organic compound capable of reversibly accepting and releasing protons. During electrochemical oxidation, AQDS releases protons that acidify the solution, causing the bound CO₂ to be released as an almost pure gas. The AQDS is then electrochemically reduced in a separate cell and recycled back into the process. This approach enabled nearly complete recovery of the previously captured carbon dioxide.
The experimental results exceeded expectations. The system operated continuously for more than 50 hours while achieving current densities of 10-50 mA/cm² – approximately an order of magnitude higher than those reported for most previously developed electrochemical DAC systems. Under certain operating conditions, it removed up to 70% of the CO₂ from the incoming air stream, reducing its concentration from about 400 to approximately 100 ppm. Applying an additional coating of ion-conducting polymers to the porous spacer further improved performance without significantly increasing energy consumption.
To evaluate the technology’s scalability, the researchers developed a computational model. It revealed that the primary limitation is no longer the chemical reaction itself, but rather the rate at which carbon dioxide diffuses from the air into the porous material. The simulations indicate that increasing porosity, reducing the thickness of the ion-conducting layers, and optimizing the internal structure could further enhance system performance.
A technical-economic analysis estimated the current cost of removing one metric ton of CO₂ at approximately USD 750. However, increasing current density, using lower-cost electricity, replacing expensive materials with inexpensive carbon-based components, and substituting the oxygen evolution reaction at the anode with the electrochemical oxidation of biomass-derived compounds such as glycerol could reduce the cost to approximately USD 150-200 per ton. Moreover, the new architecture eliminates the need for bulky air contactors, one of the most expensive components of existing direct air capture systems.
