The DOE’s Carbon Negative Earthshot underscores the need for affordable carbon dioxide (CO2) removal at the billions of tons per year scale within a decade, including direct air capture (DAC), for the US to achieve net zero emissions by 2050. To reach this goal requires: a) energy-efficient capture and removal of CO2 from ambient air, b) rapid capture, release and transport of carbon in the separating materials to manage cost, and c) manufacturable, durable materials to meet the billions of tons scale. Current DAC systems primarily rely on energy-intensive heat or pressure changes to overcome strong attachment of CO2 to liquid or solid materials that selectively capture CO2 from air. Novel alkaline anion exchange polymers (charged plastics) can capture CO2 from air and release it at higher concentrations (500x) solely with a change in relative humidity—termed a moisture swing (MS). These materials show promise to significantly reduce energy requirements as the separation is driven by water evaporation, however, they are currently limited by modest capacities to capture and transport carbon, and they become mechanically brittle when dry.
The MissionDAC project is a coordinated fundamental research investigation of MS materials to generate a comprehensive knowledge base enabling energy efficient DAC materials with improved capacities to capture and transport carbon, manufacturability, and durability. The specific objectives of this project are to: 1) reveal the energetic drivers of the moisture driven CO2 capture/release, 2) reveal and probe intrinsic chemical reaction and carbon transport limitations of MS materials while exploring the confluence of moisture and electric fields to drive fast CO2 capture and release, and 3) reveal chemical and mechanical couplings for improved performance and mechanical durability in charged polymers.
Our diverse team of scientist and engineers will combine electronic (molecular) to continuum (macro) scale computational investigations of the MS chemistry, transport, and structural mechanics in charged polymer domains. These computational studies will integrate nano- to micro-scale structural data collected using several state-of-the-art instruments including, cryogenic focused ion beam (Cryo-FIB) tomography, low-dose transmission electron microscopy (TEM), ultra-fast dynamic structural data from DOE supported synchrotrons and X-ray free electron lasers (XFEL), and polymer fractional free volume from positron annihilation lifetime spectroscopy (PALS). The rates of MS reactivity and transport will be probed using several advanced methods including, electrochemical impedance spectroscopy (EIS), quartz spring microbalance sorption (QSB), and Raman spectroscopy. These computational studies and structural / transport characterizations will be validated and interpreted with novel sorption/diffusion/flux and dynamic mechanical analysis (DMA) measurements during CO2 uptake and moisture-driven release. Initial work will probe existing MS responsive materials (e.g., strong base anion exchange resins) to inform the synthesis of new charged polymers to test our hypotheses on the impact of material structure on energy-efficient and fast MS properties with suitable chemical and mechanical properties.
At its core, this research will reveal how water, ions and polymer structures interact in nano-confined
domains across a range of water activities to impact reactivity, transport, and mechanics that span ultrafast dynamics to material lifetimes. Results from this program will inform the rational design of new DAC materials, and processes enabled by these new materials, to help meet the DOE’s Carbon Negative Earthshot objective to remove CO2 from the atmosphere and durably store it at meaningful scales for less than $100 per net metric ton (tons) of CO2-equivalent in one decade.