Spatio-Temporal Dynamics of CO2 Capture by Sorbents: Multimodal, In-Situ and Operando Measurements

Metal–organic frameworks (MOFs), which are crystalline porous materials made of organic ligands and inorganic metal nodes, are promising solid sorbents for capturing CO2 from air (direct air capture or “DAC”). However, it remains a challenge to use MOF sorbents for long-term DAC applications. Therefore, there is a need to understand the underlying chemical and structural changes that these MOFs experience during DAC operating conditions to realize MOFs with enhanced selectivity, capacity, and long-term stability. The proposed work will provide a mechanistic understanding of spatio-temporal changes in high-performance MOFs during CO2 DAC conditions using a synergistic state-of-the-art in-situ/operando experimental and computational approach. We assert that such an approach will provide design criteria for DAC anchored in mechanistic insights. Here, we will investigate changes on two distinct timescales: 1) within a single capture-release cycle to identify critical features that impart selectivity, capacity, and govern kinetics, and 2) over a high number of capture-release cycles to identify processes that lead to reduced capacity and selectivity. We will use multimodal in situ spectroscopy, X-ray crystallography, electron microscopy and synchrotron-based analyses coupled with computational modeling. We aim to investigate interactions underlying selective CO2 capture in MOFs and how they evolve during DAC operation as they undergo mechanical changes, develop heterogeneity, yield unwanted chemical reactions, or accumulate impurities. The proposal consists of three Objectives: 1) To investigate, using operando methods, the chemical and structural changes of CO2 DAC sorbents during adsorption and desorption processes. 2) To employ operando characterization methods to understand failure mechanisms of state-of-the-art MOF-based DAC sorbents and establish failure-specific accelerated aging protocols. 3) To establish design rules for MOFs with high selectivity, capacity, and longevity for DAC. The proposed program will provide a mechanistic understanding of the chemical and structural changes that occur in MOF-based DAC sorbents, shedding light on the design of robust sorbents that can operate in challenging environments. The success of this project depends on the selection of a team with a diverse background on porous materials, state-of-the-art in situ characterization, and molecular modeling. The team members have collectively pioneered the synthesis and characterization techniques that are the foundation of the proposed work, and the diverse and complementary expertise of this team will ensure the success of the program via a synergistic collaboration that brings cutting edge synthesis, operando characterization, and theory to the problem of DAC of CO2.