641 Search Results

The development of efficient CO₂ reduction technologies hinges upon a thorough understanding of the intricate interplay between solution cations and the characteristics of the electrode surface. Recently, ionic liquids (ILs) have emerged as promising electrolytes for the CO₂ reduction reaction. However, the effect of alkali cations on the electrochemical CO₂ reduction (CO₂R) reaction remains unclear in ILs. Here, in this report, we studied alkali cation effects by assessing the electrocatalytic CO₂R activity with the IL 1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM][BF₄], in water with alkali metal co-cations (i.e., Li⁺, Na⁺, and K⁺) using a polycrystalline Sn catalyst. Contrary to previous findings in purelymore » aqueous media with inorganic cations, where alkali cations strongly enhance CO₂R via pH modulation and strengthening of interfacial electric fields, alkali cations in electrolytes containing the IL [EMIM][BF4] negatively impact CO₂R activity on Sn electrodes. These results were attributed to the larger radius and higher concentration of the IL organic cation [EMIM]⁺ that mitigates the impact of alkali cations. These findings highlight the complex interplay between IL cations and alkali metals in shaping CO₂R performance.« less

Atmospheric carbon dioxide removal (CDR) is required to stabilize global temperature. CDR can be achieved via ecosystem-based approaches that are cost-effective but reversible (e.g., soil and forest management) or by more durable but expensive approaches (e.g., direct air capture coupled with geologic storage). Here, we examine trade-offs between these approaches, focusing on timing, climate impacts, and cost. We simulated reversible carbon accrual for a range of CDR contract structures using a general minimalist model of ecosystem carbon cycling, and parameterized it to simulate US agricultural soil management─specifically cover cropping─as a case study. We then quantified the resulting impact on atmosphericmore » carbon and global temperature using a climate model emulator. We find that maintaining a patchwork of reversible CDR projects by replacing lapsed projects with new projects can reduce warming by 22–195 μ°C in 2100 and that the magnitude of this cooling effect depends on how effectively the patchwork is maintained. Long-term maintenance of reversible CDR projects requires institutional stability that cannot be guaranteed over multiple decades. Consequently, effective CDR ultimately requires replacing reversible projects with durable projects. To address this problem, we modeled the cost of replacing reversible agricultural soil CDR with geologic CDR. We found that using reversible CDR as a bridge to durable CDR is potentially more cost-effective as a global cooling strategy (0.20–0.81 billion USD per μ°C avoided) than perpetual maintenance of reversible CDR (0.32–1.31 billion USD per μ°C avoided) or an immediate transition to durable CDR (1.37–2.19 billion USD per μ°C avoided). However, we emphasize that institutional commitments to maintain reversible CDR projects cannot be guaranteed. Reliance on reversible CDR as a bridge to durable CDR therefore carries an unknown amount of risk and will only function if efforts to maintain reversible CDR are robust.« less

A potential technology for the CO₂ absorption process is utilizing intensified structured packing with embedded cooling/heating channels for continuous heat exchange, which can overcome limitations of discrete methods, such as discrete intercooling and centralized reboilers, to aid in reducing energy consumption and decreasing costs. This work investigates the modeling of intensified packing (IP) for the stripper tower, extending on previous work for the absorber, which distributes heat internally within the column, improving the thermodynamics for the solvent regeneration process. The model includes submodels for steam turbine extraction to produce steam at various qualities as well as a surrogate model formore » calculating steam enthalpy. A cost model for a plant-scale absorption capture process was developed, allowing for the design of the plant to be optimized, subject to minimizing capture cost using two different power plant flue gas sources. In this optimization, the placement of IP in both towers is optimized to balance the trade-off between enhanced heat transfer and reduced mass transfer volume. For natural gas combined cycle flue gas, the standard process configuration had a minimum cost of $$\$$$$65.40/tonne CO₂, and considering IP, the minimum capture cost is reduced to $$\$$$$62.73/tonne, with utilization in the stripper column, which reduces yearly costs by up to $$\$$$$2.67 MM/yr. Cooling the absorber through IP, or intercoolers, was only found to be beneficial at higher capture rates, with IP in both towers having a cost of capture of $$\$$$$68.08/tonne at 99.9% capture, a reduction of $$\$$$$12.64/tonne when using only intercoolers at the same capture rate. When capturing from pulverized-coal power plants, the minimum cost of capture when using IP in both towers is $$\$$$$44.18/tonne (at 97% capture), while the standard configuration with and without intercoolers was $$\$$$$45.69 and $$\$$$$47.22 per tonne, respectively. This results in a reduction in yearly costs of $$\$$$$16.98 MM/yr from the base-case configuration. At this higher CO₂ concentration, cooling in the absorber from the IP becomes extremely beneficial, reducing energy consumption by up to 6%.« less

Titanium-based porous transport layers (PTLs) and iridium-based catalyst layers (CLs) are two main components of proton exchange membrane water electrolyzers (PEMWEs). PTLs are typically coated with platinum to minimize interfacial losses and to support long-term operation. Optimizing coatings and the PTL-CL interface requires comprehensive characterization. This study establishes time-of-flight secondary ion mass spectrometry (ToF-SIMS) as a valuable technique for PTL characterization, addressing capabilities and limitations related to PTL morphology. A methodology was developed that uses a Cs⁺ sputter beam for dynamic depth profiling, with data collected in both positive-ion (MCs⁺) and negative-ion modes to generate depth profiles, 2D ion maps,more » and 3D ion reconstructions. ToF-SIMS detected relative differences in platinum-layer thickness between samples; these trends were validated by cross-sectional scanning transmission electron microscope (STEM) measurements and flat-titanium substrate controls. Interfacial oxide layers are identified in both ion modes, with enhanced oxide sensitivity in negative mode. The technique’s high sensitivity enables detection of nanometer-scale coatings and trace impurities within the bulk PTL structure. These results provide a methodological framework for analyzing Pt-coated PTLs, with the potential to extend to other components in PEMWEs and other electrolyzer systems.« less

Amine-functionalized solid sorbents are a class of sorbent materials proposed for direct air capture (DAC) of CO₂, yet their long-term performance is susceptible to degradation under realistic operating conditions. Many amines are not thermodynamically stable in air, and amine sorbents oxidize while in use during DAC temperature swing adsorption processes. In this study, we investigate the role of transition metal ion contaminants, specifically Cu²⁺, Fe²⁺, and Ni²⁺, on the oxidative degradation of poly(ethylenimine) (PEI)-impregnated SBA-15 sorbents. By introducing metal ions via different modes mimicking both synthesis-related impurities and impurities derived from environmental exposure, we systematically evaluate sorbent stability after exposuremore » to dry air at an elevated temperature. Thermogravimetric CO₂ uptake measurements reveal that even trace levels of Cu and Fe (as low as ∼4 ppm) can lead to measurable sorbent deactivation after oxidative aging, despite negligible loss in the performance of the control samples. In situ infrared, UV–vis, and X-ray photoelectron spectroscopies indicate that these metals catalyze radical-driven oxidation pathways, altering the chemical structure of the sorbent and accelerating degradation. Our findings underscore the need to account for trace metal contamination during DAC sorbent synthesis and deployment and highlight the importance of environmental contamination pathways.« less

Controlling water structure and dynamics at silica interfaces are central to a wide range of technologies, including protective oxide layers for solar water splitting and nanoporous membranes. In this work, we develop a machine learning interatomic potential, trained via active learning, to achieve ab initio accuracy for water confined between hydroxylated silica surfaces over a range of silanol coverages and slit widths. We find that partially hydroxylated surfaces (50 and 75% OH) support stronger water−surface hydrogen bonding and more extended interfacial density profiles than fully hydroxylated (100% OH) surfaces, indicating that increasing OH coverage does not necessarily strengthen interfacial hydrogenbondmore » networks. Translational diffusion decreases approximately linearly with slit width and OH coverage, whereas rotational dynamics respond nonlinearly. In particular, at the smallest slit width of 5 Å, 75% OH coverage produces an enhanced local tetrahedral ordered interfacial network that strongly suppresses reorientation, while 100% coverage yields a crowded, disordered interfacial layer that also hinders rotation. In contrast, the 50% OH coverage is sufficiently sparse that it does not markedly alter water structure or dynamics under confinement. These results show that coupled control of pore size and surface chemistry enables nonlinear tuning of interfacial water structure and transport, providing a design strategy for optimizing porous silica for either enhanced interfacial stability and controlled reactivity or rapid and selective transport.« less

Dynamic processes at surfaces are central to heterogeneous catalysis, but their atomistic mechanism(s) can prove difficult to elucidate due to variations in material structure and the corresponding impact on reactivity. Moreover, disparities between reaction conditions and those employed for spectroscopic characterization at surfaces can inhibit detailed understanding of catalysis-relevant chemistries. Herein, we substantiate the so-called “cluster-surface” analogy by leveraging a low-valent tricopper architecture (1) as a model system for small molecule activation at Cu(111). Two reaction classes are explored: the adsorption of carbon monoxide (CO) and the dissociative adsorption of dihydrogen (H₂). These processes serve as an ideal testbed tomore » compare the reactivity of a molecular cluster (1) to that of a heterogeneous surface, as both reactions have empirical data from measurements performed on crystalline Cu(111). Cluster 1 reversibly binds CO. Variable temperature NMR analysis with ¹³CO reveals a favorable enthalpy but large negative entropy (−5.1 kcal × mol^–1 and −22.9 cal × mol^–1 × K^–1, respectively) for CO binding, affording a process that is marginally endergonic at room temperature (ΔG_ads(298.15 K) = 1.7 ± 0.5 kcal × mol^–1). Similarly, analogous to a Cu(111) surface, 1 is shown to oxidatively add (chemisorb) H₂. Kinetic parameters were determined for this process and the activation enthalpy (8.4 ± 0.5 kcal × mol^–1) closely mirrors that established for H₂ binding at the Cu(111) facet (6.0 to 12.4 kcal × mol^–1). Together, these results showcase that a trinuclear cluster can reproduce the small molecule binding and activation energetics of a bulk crystalline surface, setting the stage for studying less-defined surface processes in an atomically precise molecular setting.« less

Fluorinated amorphous silica–alumina (F-ASA) prepared by the thermolysis of Krossing’s Al(OC(CF₃)₃)₃(PhF) Lewis superacid supported on silica is a very reactive catalyst that promotes the pyrolysis (cracking) of aliphatic polymer melts to produce low molecular weight hyperbranched oils. Initial spectroscopic studies reported previously (Gao, J.; Perras, F. A.; Conley, M. P. J. Am. Chem. Soc. 2025, 147, 18145–18154) showed that this material contains a distribution of four-, five-, and six-coordinate aluminum sites and a small amount of Brønsted acid sites, similar to typical amorphous silica–alumina materials that are far less reactive in the pyrolysis of aliphatic polymer melts. The objective ofmore » this study was to determine whether other active sites present in F-ASA could facilitate pyrolysis reactions. This study provides evidence for the presence of a redox-active silicon oxycarbide persistent radical ((≡Si)₃C•) in F-ASA. Mims ENDOR EPR experiments show that (≡Si)₃C• is located close to aluminum. Contacting F-ASA with thianthrene (Th) results in oxidation to form the [Th^•+][F–ASA] ion-pair, while reactions with 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) result in H atom transfer to form TEMPO radical and F-ASA-H containing a mildly acidic (≡Si)₃C–H. Poisoning studies show that both Lewis acidity and (≡Si)₃C• are required for polymer pyrolysis reactivity. Finally, we propose that F-ASA promotes the formation of alkyl radicals in polymer melts, which are key intermediates in the thermal pyrolysis reactions of aliphatic polymers, involving the cooperative reactivity of both the Lewis acid and (≡Si)₃C•.« less

An extended silicate molecular cluster was used to perform density functional theory calculations to determine if an S_N2 mechanism, where OH^– attacks a Q¹ Si coupled with Na⁺ charge balancing an adjacent siloxane bridging O atom, could explain the observed energy of activation of quartz dissolution under basic conditions.

Direct air capture (DAC) compatible ionic liquids (ILs) are attractive for integrating CO₂ capture and conversion due to their high CO₂ solubility at low partial pressures, tunable chemisorption mechanisms, low volatility, and wide electrochemical windows. However, very few ILs have high CO₂ uptake at DAC conditions (420 ppm CO₂), and even fewer have been evaluated for chemical compatibility and mechanistic continuity for combined capture and electrochemical CO₂ reduction (eCO₂RR). We demonstrate that two representative DAC-capable ILs, [P₄₄₄₄][Val] (amino acid-based) and [P₆₆₆₁₄][5-Me-Imd] (azolate-based), exhibit favorable electrochemical reduction behavior. CO and H₂ were the dominant gas-phase products by GC, while ¹H andmore » ¹³C NMR confirmed negligible liquid-phase HCOOH. Chronoamperometry at moderate applied potentials (−2.0 to −2.5 V vs Ag/AgCl) in a two-compartment H-cell with a Ag coated carbon paper as the working electrode yielded steady-state current densities of ∼10 mA cm⁻² with CO FE of 96% for [P₄₄₄₄][Val] and 95% for [P₆₆₆₁₄][5-Me-Imd], highlighting the role of viscosity and chemically absorbed CO₂-IL species to provide highly selective CO formation while suppressing H₂ evolution.« less