Liquid-DAC with storage (L-DACS) requires a large amount of high-temperature heat, whereas solid-DAC with storage (S-DACS) primarily relies on low-temperature heat and electricity. Additionally, CO₂ compression energy is only relevant for storage cases, as shown in Figure 2 . Search for the perfect material At the heart of every DAC system lies a specially designed material: the sorbent that captures the CO₂. The ideal material is highly selective for CO₂, capturing as much as possible per cycle and requiring minimal energy for regeneration. It must also be durable, enduring thousands of cycles without degrading, and, perhaps most critically, it needs to be cheap enough for large- scale deployment. Currently, researchers are focusing on some major material classes, each offering its own advantages and trade-offs (see Figure 3 ). Amine-functionalised adsorbents: the current industry standard Currently, amine-functionalised materials such as polyethylenimine (PEI) or tetraethylenepentamine (TEPA) are the most widely used DAC systems due to their strong CO₂ binding capabilities. These materials are typically supported on mesoporous silica (SBA- 15), g -Al₂O₃, or other oxide supports, which provide a high surface area for CO₂ adsorption.
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L-DACS
S-DACS
L-DAC/use
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Low-temperature heat Electricity
High-temperature heat Electricity for CO compression only
Amine-based adsorbents dominate the market because they operate at low regeneration temperatures (80-120°C), making them compatible with waste heat. Their strong chemical affinity for CO₂ allows for efficient capture, even at atmospheric concentrations of 400 ppm. Additionally, their widespread study and use make them easier to commercialise. Despite their advantages, amine- degradation over time, reducing their capture efficiency due to prolonged exposure to oxygen. They are also sensitive to moisture; while some amine-based materials benefit from humidity, functionalised adsorbents face several challenges. They are prone to oxidative Figure 2 Energy needs of DACS and DAC with CO 2 use by technology Credit: IEA
Liquid -DAC solvent ( eg. KOH) Solid-DAC sorbent Amine-functionalised silica Metal-organic frameworks (MOFs) Polymer-hybrid MOFs Mixed metal oxides (MMOs) MMO-supported amines Zeolites and carbon-based adsorbents
Figure 3 Sorbents for DAC
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