Here, DAC technologies are structured according to four main CO 2 separation mechanisms: physical and/or chemical binding to either (i) a liquid or (ii) a solid material; (iii) separation based on differences in gas diffusivities; and (iv) separation by differences in freezing point (Figure ). DAC technologies that bind CO 2 to a liquid or to a solid material can be further categorized by their respective CO 2 regeneration driver (i.e., the driver that releases the CO 2 from the material it is bound to). Similarly, the separation by differences in diffusivity can be distinguished between pressure-driven processes (membrane as a sieve) and voltagedriven processes (electrochemical separation). For separation by freezing point (cryogenic separation), we solely focus on vapor-solid separation of CO 2 . This classification leads to 11 (non-exhaustive) distinct DAC technologies, listed in Table . Detailed descriptions of all technologies are provided in Section 1 in supplementary information (SI). This particular classification approach was chosen to span the technological landscape of DAC processes and highlight specific obstacles associated with each technology. This classification also allows for future incorporation of yet unknown research, development and demonstration (RD&D)