Global climate change due to rising levels of carbon dioxide in the atmosphere is one of the most significant challenges facing the global community in the coming decades. Consequently, NIST has a broad portfolio of impactful research activities that address climate change. We develop an autonomous sorbent materials foundry for the rapid evaluation of materials for direct air capture of carbon dioxide.
MMSD efforts are focused within the broad theme of Decarbonization of the economy on the topic of CDR and CCUS (carbon dioxide removal and carbon capture, utilization, and sequestration). The national significance of this work is highlighted by the Department of Commerce Strategic Plan which directs NIST to “accelerate the development of climate mitigation technologies such as carbon capture and storage…” The three principal research areas being pursued across NIST and MML within CDR and CCUS include Advanced materials for DAC (direct air capture), Carbon sequestration for building materials and Carbon dioxide conversion and catalysis. The efforts of MMSD researchers within the climate focus area comprise projects within each of these areas. MMSD researchers work cooperatively within the NIST DAC and CCUS working group, in which metrology, data, and standards development efforts toward practical approaches to reducing atmospheric carbon dioxide are coordinated across the NIST laboratories.
Metrology for Carbon Dioxide Removal and Carbon Capture, Utilization and Sequestration
Research in the MMSD climate focus area benefits significantly from access to world class synchrotron X-ray beamlines at the Advanced Photon Source and NSLS-II, enabling single crystal X-ray diffraction measurements of carbon sorbents and sequestration materials, in situ / operando characterization of adsorption processes and carbonation reactions in sequestration materials and characterization of reactive intermediates in the catalytic conversion of CO2 to high value end products. Collaborative measurements at the NCNR allows neutron diffraction characterization of carbon sorbents and sequestration materials. MMSD expertise in autonomous experimentation and machine learning (ML) algorithm development is being applied to the DAC materials discovery problem. MMSD competence in nanocalorimetry is used to address the challenging metrology problem of assessing cycle durability in prospective carbon capture materials. Computational capabilities are essential to the MMSD climate focus area, including the use of density functional theory (DFT) in modeling porosity and gas adsorption, and the use of computational X-ray spectroscopy in the characterization of catalytic intermediates in CO2 conversion reactions.
Characterization of Advanced Materials for Carbon Capture
The capture of carbon dioxide from high concentration point sources or directly from air is fundamentally a materials science problem. The discovery and development of materials that allow the execution of this capture process in a carbon negative way is a central challenge to achieving global climate goals. The technical needs for the process of discovery and optimization of the materials necessary to address this challenge range broadly across synthesis, structural and chemical characterization, and metrology for process performance and long-term durability. MMSD researchers, working collaboratively within the NIST DAC and CCUS working group, are actively addressing problems in each of these key areas.
Structure property relationships in porous materials for carbon capture applications — The development of structure property relationships for porous carbon capture sorbents and membranes is essential for the discovery and optimization of the most effective materials. Utilizing world class X-ray and neutron metrology facilities, MMSD researchers employ a combination of single crystal, X-ray diffraction structure determination, density functional theory-based calculations of pore structure and simulations of gas adsorption, coupled with in situ X-ray scattering measurements of structural changes under model operating conditions to study structure property relationships in flexible metal organic framework (MOF) sorbent materials. Considerable effort has been directed to the study of pillared cyanonickelate MOFs, a promising material for carbon capture applications in which the pore size, chemistry and structural dynamics can be varied through choices of ligands and pore functionality. The synchrotron based, small angle X-ray scattering and X-ray diffraction measurements have also been applied to the study of amine-impregnated silica sorbents envisioned for DAC applications. This work is a significant contribution to a benchmark set of structural and performance characterizations being done on selected DAC candidate materials across the NIST laboratories within the DAC-CCUS working group. MMSD researchers have also recently initiated the establishment of a synthesis laboratory with a pilot project on metal-organic framework (MOF) compounds to facilitate access to advanced materials necessary for metrology development.
AI for Climate Change: Guiding Discovery of Sorbent Materials for CO2 Direct Air Capture — The need for DAC to be strongly carbon-negative and to operate at dilute atmospheric conditions imposes strict performance requirements on the materials. Therefore, there is a pressing need to quickly identify and evaluate sorbent materials for DAC. MMSD has developed a machine learning (ML) algorithm to guide experimentalists to likely high-performing candidate materials from their atomistic structure. The NIST Adsorption Database has been expanded to include more theoretical calculations of adsorption isotherms and to facilitate computational correlation of adsorption isotherms with material properties. Additional efforts are focused on the development of a robust performance metric for sorbent materials in DAC applications and envisioning an autonomous experimental system for efficiently evaluating candidate materials for DAC applications. Work has also begun on the development of an autonomous, high throughput materials characterization system to study the synthesis of porous materials for DAC applications. The aim of this platform development is to generate much-needed standardized datasets on porous material synthesis and the dissemination of the platform design and associated ML algorithms to further accelerate research on DAC materials development.
Nanocalorimetry for DAC Materials Characterization — Nanocalorimetry is a measurement technique able to explore the thermal behavior of materials at faster rates on smaller length scales than traditional bulk thermal techniques during processes such as adsorption/desorption. MMSD is exploring the use of nanocalorimetry to characterize the adsorption/desorption process in a model amine-impregnated, silica DAC sorption material that is being studied broadly at NIST in the CDR and CCUS working group. Initial data shows that nanocalorimetry can measure the thermal signatures of the adsorption and desorption events and help to select suitable sample activation procedures. Additionally, nanocalorimetry is being used to significantly accelerate thermal cycle stability evaluation during the adsorption-desorption process, a sorbent material characteristic that is critical to field performance and viability but challenging to measure via traditional methods. MMSD is also developing a new nanocalorimeter to enable transmission electron microscope observation during thermal measurements to relate changes in the material structure to the energies of sorption and desorption.
The capture of carbon dioxide, either directly from the air or from industrial point source emissions, leads directly to the next challenge of ensuring its permanent removal from the atmosphere. NIST has an active research program in carbon sequestration for building materials where the need for validated test methods and standards for quantifying carbon content is acute. Similar needs exist for plans to permanently sequester CO2 in geologic formations. Central to both approaches is the need to understand the underlying chemistry of carbonation reactions under relevant conditions. MMSD staff are utilizing X-ray scattering and diffraction to study structure changes in sequestration materials during carbonation reactions.
Structure measures of CO2 sorption processes in carbon sequestration materials — Carbonation reactions are central to the process of permanent carbon sequestration, either in building materials (hydrating cements) or in geologic formations (silicates). MMSD staff utilize NIST access to state-of-art neutron and X-ray facilities, in conjunction with MML and NCNR collaborators, to detect the effects of carbonation in model sequestration materials. Synchrotron based small angle X-ray scattering and X-ray diffraction have been used to probe structural changes on multiple length scales in both type so materials. Ex-situ studies of several cement formulations hydrated under CO2 and N2 indicate that the structural changes that accompany carbonation can be quantified using these techniques. Similar conclusions were drawn from in-situ measurements on olivine, a model silicate mineral, under various flowing CO2 and N2 conditions. Further development of these quantitative studies will allow investigation of critical structure–composition and structure–performance relationships. The fundamental understanding of carbonation reactions derived from these measurements will inform broader NIST efforts to develop validated methodologies to quantify carbon in sequestration materials.
Catalysis for Carbon Dioxide Conversion
The utilization of carbon dioxide captured from carbon intensive industrial processes (e.g., steel and cement manufacturing) as a feedstock for production of high value chemicals and fuels is an important step towards sustainable manufacturing. The development of suitable catalysts is of critical importance to replace current processes based on hydrocarbon feedstocks. The chemical stability of CO2 makes these conversion reactions challenging to execute in a carbon efficient manner, also driving the need for discovery of new catalysts. MMSD is developing an X-ray spectroscopy testbed that will provide a powerful new way to investigate catalytic intermediates central to understanding these important chemical processes.
Development of a First-of-Kind X-ray Testbed for Breakthrough Catalyst Measurements — The transition to a sustainable, carbon-neutral economy requires breakthrough catalysts for the conversion of captured CO2 emissions into fuels and chemicals thus enabling carbon efficient manufacturing. MMSD is engaged in a NIST Innovations in Measurement Science (IMS) project beginning in FY23 to develop a catalyst measurement testbed that will provide in-operando characterization of industrial catalysts via X-ray spectroscopy. The testbed will achieve unparalleled chemical sensitivity by using resonant X-ray excitation to simultaneously probe occupied and unoccupied electronic states thus revealing detailed chemical fingerprints that characterize working catalysts. Working together with PML and the MML Chemical Sciences Division, this project aims to produce sensors that greatly push the current limits of soft X-ray instrument design, integrated with a versatile, high-throughput operando reactor at the NIST soft X-ray beamline at the National Synchrotron Light Source (NSLS)-II. The capabilities of the NIST computational X-ray spectroscopy code OCEAN, developed by MMSD, will be expanded, and used with custom microkinetic models for accurate, rapid simulations of catalytic intermediates. The final product will be a new detector, a catalyst measurement cell, and improved computational tools, integrated into a single measurement testbed that will provide NIST, industry, and academic partners a powerful new tool to measure and understand catalytic reactions. This program will accelerate NIST-industry collaborations on the breakthrough sustainable reactions underpinning the transition to a carbon-neutral economy (e.g., conversion of CO2 to methanol) and advance a new generation of detectors with broad utility across the scientific enterprise.