The urgency to address global climate change induced by greenhouse gas emissions is increasing. In particular, the rise in atmospheric CO2 levels is generating alarm. Technologies to remove CO2 from ambient air, or “direct air capture” (DAC), have recently demonstrated that they can contribute to “negative carbon emission.” Recent advances in surface chemistry and material synthesis have resulted in new generations of CO2 sorbents, which may drive the future of DAC and its large‐scale deployment. This Review describes major types of sorbents designed to capture CO2 from ambient air and they are categorized by the sorption mechanism: physisorption, chemisorption, and moisture‐swing sorption.

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Direct air capture (DAC) shows exceptional promise for carbon dioxide removal on the scale required to fulfill the Paris Agreement. Even though planetary limitations do not constrain the scale of DAC, the currently high cost puts its feasibility in question. By observing cost reduction pathways of similar technologies, this paper explores the cost reduction opportunities that result from learning-by-doing. We developed an analytical buy-down model to investigate what it would take to lower the cost of DAC to $100/ton CO2. Our goal is not to accurately predict future costs, but our analysis demonstrates that if DAC follows a path similar to that of comparable, successful technologies, a capital investment of several hundred million dollars could buy down the cost of DAC. This buy-down effort at a relatively low cost will quantify the learning potential of DAC and show whether its costs can be reduced (like solar photovoltaic modules) or whether despite the investment it remains expensive (like nuclear power generation).

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This analysis investigates the cost of carbon capture from the US natural gas-fired electricity generating fleet comparing two technologies: Post-Combustion Capture and Direct Air Capture (DAC). Many Natural Gas Combined Cycle (NGCC) units are suitable for post-combustion capture. We estimated the cost of post-combustion retrofits and investigated the most important unit characteristics contributing to this cost.Units larger than 350 MW, younger than 15 years, more efficient than 42% and with a utilization (capacity factor) higher than 0.5 are economically retrofittable. Counterintuitively, DAC (which is usually not considered for point-source capture) may be cheaper in addressing emissions from non-retrofittable NGCCs. DAC can also address the residual emissions from retrofitted plants. Moreover, economic challenges of post-combustion capture for small natural gas-fired units with low utilization, such as gas turbines, make DAC look favorable for these units. Considering the cost of post-combustion capture for the entire natural gas-related emissions after incorporating the impact of learning-by-doing for both carbon capture technologies, DAC is the cheaper capture solution for at least 1/3 of all emissions. File list (2)download file view on ChemRxiv Manuscript.pdf (787.09 KiB) download file view on ChemRxiv SI.pdf (476.25 KiB)