Accelerated Testing of PEI-Silica Sorbent Pellets for Direct Air Capture
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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Spieles, Aaron James [Sandia National Laboratories↗
Electrolyte–Electrocatalyst Interfacial Effects of Polymeric Materials for Tandem CO 2 Capture and Conversion Elucidated Using In Situ Electrochemical AFM
Integrating CO 2 capture and electrochemical conversion has been proposed as a strategy to reduce the net energy required for CO 2 regeneration in traditional CO 2 capture and conversion schemes and can be coupled with carbon-free renewable electricity. Polyethylenimine (PEI)-based materials have been previously studied as CO 2 capture materials and can be integrated in these reactive capture processes. PEI-based electrolytes have been found to significantly increase the CO 2 loading, and impact selectivity and rate of product formation when compared to the conventional aqueous electrolytes. However, the influence of these materials at the catalyst–electrode interface is currently not well understood. In this study, PEI-based electrolytes were prepared and their impact on the morphology of a silver electrode performing electrochemical CO 2 reduction (CO 2 R) was studied using in situ electrochemical atomic force microscopy (EC-AFM). The presence of PEI on the electrode surface could be distinguished based on nanomechanical properties (DMT modulus), and changes were observed as negative polarization was applied, revealing a reorganization of the PEI chains due to electrostatic interactions. These changes were impacted by the electrolyte composition, including the addition of supporting electrolyte KHCO 3 salt, as well as CO 2 captured by the PEI-based electrolyte, which minimized the change in surface mechanical properties and degree of PEI alignment on the electrode surface. The changes in surface mechanical properties were also dependent on the PEI polymer length, with higher molecular weight PEI showing different reconfiguration than the shorter polymer brushes. The study highlights that the choice of polymer material, the electrolyte composition, and CO 2 captured impact the nearelectrode environment, which has implications for CO 2 R, and presents EC-AFM as a new tool that can be used to probe the dynamic behavior of these interfaces during electrocatalysis.
36 MATERIALS SCIENCE↗
Photoreactive Capture and Conversion of Dilute Carbon Dioxide into Synthetic Natural Gas
This study introduces a photoreactive system that integrates the capture of dilute CO 2 streams with their catalytic conversion to synthetic natural gas (CH 4 ), utilizing a Ru nanoparticle (NP)-doped TiO 2 composite loaded with linear polyethylenimine (L-PEI) and enhanced with plasmonic titanium nitride (TiN). This light-driven approach mitigates challenges that have plagued traditional thermal reactive carbon capture (RCC) methods, such as CO 2 slip and amine degradation. We demonstrate that L-PEI enables stable CO 2 capture and conversion, achieving ~70% conversion of captured CO 2 to CH 4 across multiple reaction cycles using nonflammable forming gas (~5% H 2 ) as the reductant. In contrast, branched PEI (B-PEI)-loaded composites exhibited significant catalyst deactivation after several RCC cycles. Scanning transmission electron microscopy (STEM) imaging confirms that significant sintering of the Ru NPs occur in the B-PEI sample under RCC conditions, whereas their size remains stable in more rigid L-PEI composites. Technoeconomic analysis (TEA) estimates that CH 4 production using this system could cost less than $\$$5/kg based on current electrocatalytic H 2 prices. These results represent one of the most promising demonstrations of amine-based RCC employing dilute CO 2 sources to date.
36 MATERIALS SCIENCE↗
Role of Polymer Architecture in CO 2 Capture from Air Using Supported Poly(alkylenimine)s: Linear vs Branched Polymers
Direct air capture (DAC) of CO 2 coupled with geologic storage is a promising climate change mitigation strategy, with some applications employing amines supported on porous solids as CO 2 sorbents. While branched poly(ethylenimine) (PEI) is the standard benchmark amine material, it suffers from limited oxidative stability. Poly(propylenimine) (PPI), as an alternative, has previously demonstrated improved resistance to degradation under harsh oxidative conditions. Linear and branched PEI are commercially available, though at different molecular weights, while PPI is not commercially available. For this reason, a comparative study of all four polymers (linear PEI, branched PEI, linear PPI, branched PPI) has not been reported for DAC. In this study, we synthesize and compare low-molecular-weight (∼800 g/mol) linear (L) and branched (B) PEI and PPI supported on a model support, SBA-15 silica. These materials are evaluated for CO 2 adsorption under dry, DAC-relevant conditions (400 ppm of CO 2 , 30 °C). LPPI exhibited the highest amine efficiency at all loadings, reaching a maximum of 0.14 mmol CO 2 /mmol N, outperforming BPEI, while LPEI consistently showed the lowest uptake capacity. Temperature-programmed desorption reveals that the structure of the amine polymer impacts the CO 2 binding strength, with branched polymers displaying higher desorption energies of 102−111 kJ/mol. In situ infrared spectroscopy experiments show that all sorbents preferentially capture CO 2 as ammonium carbamate. Isobaric CO 2 uptake studies further underscore the influence of polymer mobility and support pore crowding on performance, while demonstrating the sorbents’ performance at elevated temperatures and CO 2 concentrations. All materials demonstrated good stability over 25 adsorption−desorption cycles using thermal regeneration in an inert gas purge, with only BPPI displaying a 10−11% decrease in capacity/amine efficiency during cycling, possibly due to the loss of low molecular weight, oligomeric amines. This is the first side-by-side comparison of the CO 2 sorption properties of linear and branched PEI and PPI with similar molecular weights. These findings highlight the significant role of polymer architecture in CO 2 capture efficiency and inform future designs of durable, high-performance DAC sorbents.
adsorbents↗
Design and Characterization of Hybrid Multilayer Structures: Layer-by-Layer Growth of Polymer and Graphene Oxide Assemblies and Their Utility in Fuel Cell Applications
We report the layer-by-layer growth of poly- (ethylenimine) (PEI) that has been modified with sulfamate functionalities (S-PEI) using Zr 4+ -complexation interlayer linking chemistry. We have also deposited adlayers of graphene oxide (GO) that have been modified to possess sulfate functionalities (SGO), onto the S-PEI layers. The multilayer assemblies are formed with sulfamate/sulfate and sulfate/sulfate (S-PEI + S-GO) interlayer linking chemistry. In all cases the adlayer thickness is consistent with predictions based on van der Waals volume and/or molecular mechanics calculations. X-ray photoelectron spectroscopy (XPS) is used to characterize the Zr/S stoichiometry in the multilayer assembly. The utility of these hybrid multilayer structures is demonstrated in a Proton Exchange Membrane (PEM) fuel cell, where they are shown to reduce H 2 gas crossover by 15% with only a 12 nm thick layer.
fuel cell↗
Photo-Reactive Amine-Based Direct Air Capture and Conversion of CO2
This study presents a novel photochemical approach to direct air capture (DAC) and CO2 conversion, utilizing a ruthenium-modified mesoporous TiO2 composite infused with linear polyethyleneimine (L-PEI) and enhanced by light absorbing and earth abundant titanium nitride (TiN). This light-activated system operates at ambient pressure and addresses long-standing challenges in conventional amine-based thermal reactive carbon capture (RCC), including amine degradation and CO2 slip. Our findings demonstrate that L-PEI effectively stabilizes CO2 adsorption and facilitates high-yield methanation over 50 cycles with a non-flammable forming gas mixture (approximately 5% H2). Comparatively, composites incorporating small-molecule amines exhibited poor stability under illumination, while highly mobilie branched PEI (B-PEI) formulations suffered from significant catalyst deactivation. A technoeconomic analysis suggests that methane synthesis via this platform could be achieved at costs below $5/kg under current electrocatalytic hydrogen pricing. These findings highlight the potential of this approach to enhance energy security by enabling decentralized, scalable fuel production from atmospheric CO2.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A scalable and autoclavable oxygen nanosensor platform for metabolic monitoring of Saccharomyces cerevisiae in a bioreactor and other in situ systems
Polymer-encapsulated dye nanoparticle sensors are a valuable approach to achieving in situ analyte measurements with luminescence; however, typical emulsion-based nanosensors are poorly suited for large-scale biological samples due to limitations of synthesis scalability and stability. Branched polyethylenimine (PEI) is a versatile polymer scaffold ideal for constructing nanoparticles with various covalently conjugated moieties due to their high density of reactive primary amines, high water solubility, and biological stability. In this work, we used branched polyethylenimine as a scaffold-based approach for making a stable and scalable ratiometric oxygen sensor. Pt (II) tetracarboxyporphine was used as an oxygen-sensing dye and coumarin 343 as a reference dye, all covalently linked to the PEI scaffold producing a product that could withstand sterilization procedures and easily be scaled. To minimize toxicity from the PEI scaffold, we conjugated it with 2000 MW PEG. The applicability of the sensors was demonstrated in a 200 mL Saccharomyces cerevisiae yeast culture, using orthogonal luminescent and electrochemical oxygen measurements to validate sensor response and measure the metabolic activity of the yeast in our culture. Further, this approach was able to match the sensitivity of our electrochemical measurements while improving upon drawbacks of other luminescent methods of oxygen detection, demonstrating effective monitoring for at least 20 h. Our scaffold-based approach is a modular and easily translatable technology that could be useful in various biotechnological applications.
59 BASIC BIOLOGICAL SCIENCES↗
Ammonium-coordinated exchanger (ACE) functionalized silica sorbents for recovering/removing aqueous anionic contaminants
There are limited studies of functionalized silica anion exchange sorbents used for critical/heavy metal recovery/removal relative to polymeric and other inorganic materials. This work features ammonium-coordinated exchanger (ACE) anion exchange particle sorbents prepared by either acid-washing epoxy-crosslinked polyethylenimine (PEI) hydrogen bonded within/to a silica particle sorbent (two-step method) or reacting a di-chlorinated crosslinker, α,α-dichloro-p-xylene (DPX), with PEI within silica (single-step method). Energy dispersive X-ray spectroscopy (EDS) and infrared spectroscopy confirmed the presence of -NH 2 + ···Cl - and -NH 3 + ···Cl - groups, which removed oxyanionic species –arsenate, selenate, chromate, sulfate, phosphate, and nitrate– plus bromide from ideal solutions, authentic acid mine drainage (AMD), and authentic flue gas desulfurization (FGD) wastewater. Affinity of the anions for ACE varied across single- and mixed-element solutions. However, affinity for CrO 4 2- was among the highest in both cases. Total anion uptake by the optimized ACE, PEI-E3-HCl_1.1, reached 1.2 mmol anion/g-sorb. (0.56 mmol CrO 4 2- /g), or ∼2.3 mmol negative charge/g-sorb. This was close to the 0.52 mmol CrO 4 2- /g of a commercial anion exchange resin. Near-consistent removal of 20–80 % of each anion from FGD during an eight-cycle adsorption-desorption (1 M NaCl) test predicted good ACE viability for testing under practical conditions at larger scale.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Performance Degradation of Amine-Infused Fiber Sorbents for Direct Air Capture: Mechanisms and Solutions
Sorbent stability poses significant impacts on longterm performance of direct air capture (DAC) of CO 2 and levelized cost of capture (LCOC). We report the DAC performance degradation of amine-infused fiber sorbents based on poly(ethylenimine) (PEI), mesoporous SiO 2 , and cellulose acetate (CA) over CO 2 cyclic sorption cycles in a nonoxidative environment. Infrared and nuclear magnetic resonance spectra indicate that the aminolysis reactions between CA ester moieties and PEI amine sites lead to the formation of acetamides and hence lower CO 2 affinities of the sorbents. This stability issue can be remedied by hydrolysis treatment of the CA fiber sorbents before PEI impregnation or replacing CA with poly(ether sulfone). This study underscores the importance of selecting proper support or additive materials of DAC contactors that are compatible with active species of CO 2 capture.
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CO 2 Capture Characteristics of Hyperbranched Poly(alkylene imine): A Molecular Dynamics Simulation Approach
This study explores the CO 2 capture characteristics of hyperbranched poly(ethylenimine) (HB-PEI) and poly- (propyleneimine) (HB-PPI) through molecular dynamics simulations using density functional theory-calibrated force fields. Key features such as density, free volume, glass transition temperature, CO 2 /H 2 O distribution, and molecular diffusion are systematically investigated to elucidate structure−function relationships under dry and hydrated conditions. HB-PEI demonstrates a slightly higher density and lower free volume compared to HB-PPI yet shows superior CO 2 capture due to the high amine concentration. Glass transition analysis indicates a higher thermal mobility in HBPEI, enhancing the CO 2 diffusivity. Pair correlation and coordination analyses confirm a stronger affinity of CO 2 with primary and secondary amines, particularly in hydrated environments where water competes with CO 2 for binding sites. Despite its more compact structure, HB-PEI outperformed HB-PPI in CO 2 and H 2 O transport, as confirmed by higher diffusion coefficients across all hydration levels. These findings highlight a critical balance among polymer architecture, amine accessibility, and hydration in designing next-generation solid amine sorbents for efficient direct air capture applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Chemical Vapor Deposition-Grown Hexagonal Boron Nitride and Graphene for Tandem Dielectric Capacitive Polymer Devices
To address the low energy density of polymeric capacitors, this work explores how tandem combinations of antagonistic properties can enhance energy storage. We introduce multilayer architecture integrating chemical vapor deposition (CVD)-grown ≈2 nm hexagonal boron nitride (hBN) and graphene with ferroelectric polyvinylidene fluoride (PVDF) and linear polyetherimide (PEI) layers to suppress leakage paths, reduce loss, and promote Maxwell–Wagner–Sillars polarization. Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and plasma focused ion beam (PFIB) analyses confirm robust material integration. In conclusion, for the tandem device, E BD ≈600 V/μm, while individual layers show lower values (PVDF|Graphene (Gr)|PVDF ≈ 50 V/μm and PEI|hBN|PEI ≈ 275 V/μm), yielding an overall ≈6000% enhancement and demonstrating the effectiveness of the 2D multilayer design.
Chemical vapor deposition (CVD)↗
Bench-Scale Testing of Monolithic PPI Structured Contactors for Direct Air Capture of CO 2
The overall project objective was to develop, optimize and bench-scale test the integrated embodiment of a leading direct air capture (DAC) sorbent composition, linear-poly(propylenimine) (l-PPI), in a structured material system, specifically a monolithic contactor for achieving low pressure drop, to justify its further scale-up in a subsequent program. The project team was led by CORMETECH, a leading monolithic gas/solid contactor manufacturer for environmental applications, and included Global Thermostat, a well-known DAC start-up, and Georgia Tech, a prominent US academic institution in carbon capture and DAC. The monolithic contactor for l-PPI in this project employed an advanced, cost-effective fabrication technique from CORMETECH, namely a porous monolith substrate directly impregnated with the amine, an approach contrasting to the traditional wash-coating methods used for activating monoliths. The l-PPI monolithic contractor is targeted for use in DAC systems such as the Global Thermostat DAC process, which involves the cyclic operation of ambient air flow over a monolithic amine contactor followed by steam-mediated thermal desorption and CO 2 collection, maximizing volumetric productivity while reducing the auxiliary power required to capture CO 2 from air. The Global Thermostat DAC process currently utilizes poly(ethyleneimine) (PEI) materials as baseline sorbents, which are subject to oxidative degradation and slow capacity fade at the elevated temperature required for efficient CO 2 removal. Georgia Tech, with Global Thermostat, had discovered in lab-scale efforts that l-PPI had superior resistance to oxidative degradation compared to PEI, with similar CO 2 adsorption capacity. While the novel l-PPI sorbent offers significant advantages over PEI for DAC, including potential design simplification and increased process efficiency, it is not commercially available, and prior to this project, had not yet been evaluated on the bench-scale in a structured contactor.
36 MATERIALS SCIENCE↗
Lewis Acid‐Activated Charge Trapping in Dielectric Polymers for Superior High‐Temperature Electrostatic Energy Storage
Dielectric polymer capacitors are essential for electrostatic energy storage but suffer from charge transport-induced energy losses, particularly at elevated temperatures where thermally activated charge carriers exacerbate conduction. Conventional mitigation strategies rely on introducing heterogeneous interfaces to create charge traps, complicating scalable film fabrication. A homogeneous molecular trapping mechanism would circumvent these complexities, yet remains underexplored. Herein, a charge trapping strategy is devised by modifying the lowest occupied molecular orbitals of dielectric polymers through Lewis acid-base adduct formation. The use of tris(pentafluorophenyl)boron (BCF) as a Lewis acidic molecular additive introduces deeper charge traps in commercial polyetherimide (PEI) while retaining homogeneity. With only 0.5 wt.% loading, the PEI-BCF film exhibits greatly improved breakdown strength, achieving an ultrahigh discharged energy density of 7.3 J cm-3 with excellent cycle stability at 200 °C. This work establishes a facile molecular approach to decoupling charge trapping from heterogeneous interfaces, enabling high-energy-density polymer capacitors operable under extreme thermal conditions.
Fan, Lu↗
Electrically Conductive Amine Functionalized Reduced Graphite Oxide Foam for CO 2 Removal from the Air
Rapid regeneration of CO 2 adsorbents is critical to improving the productivity of direct air capture (DAC) systems. In this study, we codesigned a material to have appropriate electrical conductivity and CO 2 adsorption properties to enable efficient CO 2 capture from air. Specifically, we present a poly(ethylenimine) (PEI)-impregnated thermally annealed graphite oxide (TAGO900) foam adsorbent tailored for vacuum-assisted electrically driven thermal swing adsorption (V-ETSA). This structured adsorbent leverages the high electrical conductivity of the reduced graphite oxide framework to enable fast and direct heating of the adsorbent material by electrical resistance heating (Joule heating). An optimal sample, 40 wt % PEI (molecular weight 25k) impregnated TAGO900, shows the best balance between adsorption capacity (1.54 mmol g –1 ) and adsorption rates (0.016 mmol g –1 min –1 ) using fixed bed breakthrough experiments at 25 °C and 70% RH using 50 sccm 400 ppm of CO 2 /N 2 flow. Compared to conventional temperature vacuum swing adsorption (TVSA), the V-ETSA approach achieves substantially faster CO 2 desorption, achieving average desorption rates (including cooling time) of 0.09 mmol g –1 min –1 ─approximately 2.5 times faster than TVSA under similar operating conditions. The maximum desorption rate reaches 0.23 mmol/g/min during the desorption stage. These results underscore the importance of the direct heating strategy, such as Joule heating, for fast and highly productive vacuum swing adsorption in DAC systems.
amines↗
Effect of Storage Conditions on Efficacy of Poly(ethylenimine)-Alumina CO 2 Sorbents
Solid amine sorbents are one of the primary components of DAC technologies that allow for the removal of ultradilute CO 2 from the atmosphere. A main drawback in the implementation of solid amine sorbents in industrial-scale DAC applications is their instability under certain operational or storage conditions over an extended period. In this work, the effect of storage temperature and gas composition in the storage headspace on the long-term stability of a poly(ethylenimine)-alumina (PEI/γ-Al 2 O 3 ) sorbent is explored. PEI/γ-Al 2 O 3 sorbents with 70 and 100% pore filling are aged under varying gases (N 2 , O 2 , Ar, 0.04% CO 2 −N 2 , CO 2 , and ambient air) in an oven (40 °C), at common ambient indoor temperature conditions (23 °C), or in a freezer (−4 °C). The CO 2 sorption capacity, as measured by thermogravimetric analysis (TGA), along with FTIR spectra of the fresh and aged sorbents, reveal that at 23 and −4 °C, storage under ambient air or inert gas (Ar) provides reasonable long-term stability, with <13% degradation over 12 and 5 months of storage. Interestingly, with storage at 40 °C, similar levels of deactivation were observed under pure O 2 and N 2 after 4 months of storage, which suggests that nonoxidative thermal reactions can occur under prolonged storage conditions under N 2 . In contrast, with storage under CO 2 , sorbent degradation is substantially suppressed compared to storage under N 2 , ambient air, O 2 , or Ar, yielding sorbents with no observable loss in capacity after 2 months, compared to a 66, 63, and 62% loss under N 2 , ambient air, and N 2 in the same period at 40 °C, respectively. Overall, these findings provide guidance for practical amine sorbent storage in academic or industrial settings where amine sorbents are used for carbon capture.
Atmospheric chemistry↗
Development of Next-Generation Additive Chemistry for Direct Air Capture Sorbents (CRADA Final Report)
Introducing antioxidant additives into amine-based DAC sorbents can extend their lifetime. These sorbents are readily prepared by physically mixing additives with amines, a straightforward approach using commercially available materials. Advancing this strategy requires understanding how additives function under varying conditions, especially humidity. This project aims to reveal how humidity and additive chemistry influence oxidative degradation of PEI-based sorbents, levereging LLNL’s expertise in physics-based computational modeling, and Global Thermostat (GT)’s expertise in materials synthesis, characterization, and degradation kinetics testing, to gain fundamental insights into the chemistries and mechanisms of PEI oxidative degradation, and develop design principles that enhance sorbent durability.
36 MATERIALS SCIENCE↗
Work In Progress: Using Internships as Means for Indirect Assessment of ABET Criteria 3 “1-7” Student Outcomes
The Electrical & Computer Engineering (ECE) Department at Portland State University (PSU) has developed a Power Engineering Internship (PEI) program that provides engineering career development pathways within the electric utility industry. The PEI is supported by several U.S. Department of Energy grants that aim to develop quality career opportunities and develop a future electric utility workforce that represents the nation’s diverse populations. The PSU ECE Department intends to use surveys of internship participants as assessment tools for its ABET accreditation process, in particular, the ABET Criteria 3 Student Outcomes (SOs). SOs relate to the knowledge, skills, and behaviors that students acquire as they progress through an engineering program [1]. They describe what engineering students are expected to know and should be able to do by the time they graduate. Engineering education literature presents multiple methods for using internships as means for assessing SOs. Methods include using self-assessments that derive from internship experiences as well as mapping survey responses from employers and interns to SOs. Such methods gain value as they are assessed over multiple years. However, the majority of this literature discusses assessment tools that were developed for the ABET 2000 Criteria 3 “a through k” SOs. One of our motivations is to provide assessment tools that can be used to assess modern Criteria 3 SOs based on students’ internship experiences.
Bass, Robert [Portland State University]↗