Water-Enhanced Direct Air Capture of Carbon Dioxide in Metal–Organic Frameworks
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Chemistry↗
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Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Cambered Bipyridyl Ligand with Extended Aryl System Enables Electrochemical Reduction of Carbon Dioxide and Bicarbonate by Mn(bpy)(CO) 3 Br-type Catalyst Immobilized on Carbon Nanotubes
Heterogeneous materials containing molecular catalytic sites show promise for electrocatalytic reduction of CO 2 to energy-enriched carbon products. Interactions between the catalyst and the heterogeneous support increasingly are recognized as important in governing product selectivity and rate. Recent work on Mn(R-bpy)(CO) 3 Br type catalysts immobilized on multiwalled carbon nanotubes (MWCNT) demonstrated control of electrocatalytic behavior with steric modification of the molecular catalyst. Phenyl groups installed in the 4,4' positions of the bipyridine ligand (ph-bpy) maximized performance through π–π interactions with the MWCNT support. Herein we report the outcome of extending the ligand π system with Mn(nap-bpy)(CO) 3 Br (nap-bpy = 4,4'-di(naphthalen-1-yl)-2,2'-bipyridine) and Mn(pyr-bpy)(CO) 3 Br (pyr-bpy = 4,4'-di(pyren-1-yl)-2,2'-bipyridine) immobilized on MWCNT. We demonstrate exceptional electrocatalysis with Mn(nap-bpy)(CO) 3 Br/MWCNT (FE CO > 92%; J CO = 16.5 mA/cm 2 ) and find that this catalyst electrochemically reduces bicarbonate in the absence of deliberately added CO 2 at a remarkable overall selectivity of >80% for carbon products (FE HCOO – = 52% and FE CO = 29%). We show diminishing returns to simply adding aromatic character to the bipyridyl ligand with Mn(pyr-bpy)(CO) 3 Br/MWCNT and observe a unique cambering of the Mn(nap-bpy)(CO) 3 Br bipyridyl ligand that we believe enables selective catalysis. Mechanistic studies were carried out on Mn(nap-bpy)(CO) 3 Br/MWCNT using a novel thin-film infrared spectroelectrochemical (IR-SEC) technique. These experiments observe the immobilized Mn(nap-bpy)(CO) 3 Br undergo single electron reduction to a Mn-centered radical that binds CO 2 in a reduction-coupled process.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Phase Change-Mediated Capture of Carbon Dioxide from Air with a Molecular Triamine Network Solid
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Selective Reduction of Carbon Dioxide in Water Using [M(bpy2+)(CO)3(I)]2+ (M = Mn, Re) Electrocatalysts with Pendent Cations
Manganese(I) carbonyl complexes are promising electrocatalysts for CO2 reduction, yet their application in homogeneous aqueous media remains limited by poor solubility and selectivity. Here, we report water-soluble Mn(I) and Re(I) complexes fac-[M(bpy2+)(CO)3X]2+ (X = I or Cl), featuring bipyridine ligands functionalized with -Ph-CH2-(NMe3)+ cationic ammonium groups that integrate water solubility with secondary-sphere stabilization. In bicarbonate buffer at pH 6.8, the Mn catalyst is completely selective for CO production at a low overpotential (η = 0.3 V), operating by a protonation-first mechanism with observed rates of ~10 s−1. Pulse radiolysis reveals that the one-electron reduced Mn species undergoes dimerization in the absence of CO2 but uniquely reacts competitively with CO2 through an initial pre-equilibrium followed by fast formation of a dinuclear CO2-bridged species (ΔGo = −12.4 kcal mol−1). At a higher 0.6 V over-potential, a faster reduction-first pathway (~100 s−1) is available upon reduction of the metallo-carboxylic acid intermediate, Mn-CO2H2+; however, this regime is functionally limited by the formation of a resistive, noncatalytic film on the electrode surface. Comparison to the analo-gous water-soluble Re catalyst (kobs = 440 s−1, η = 0.6 V) highlights the distinct mechanistic ad-vantages of earth-abundant Mn in low-potential catalysis. These results demonstrate how cati-onic second-sphere design enables selective, homogeneous CO2 reduction in water while reveal-ing competing radical and electrode-mediated processes that govern catalytic performance.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Formation of Carbon-Induced Nitrogen-Centered Radicals on Titanium Dioxide under Illumination
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electrical Properties of Carbon Dioxide Hydrate: Implications for Monitoring CO 2 in the Gas Hydrate Stability Zone
CO 2 and CH 4 clathrate hydrates are of keen interest for energy and carbon cycle considerations. While both typically form on Earth as cubic structure I (sI), we find that pure CO 2 hydrate exhibits over an order of magnitude higher electrical conductivity ( σ ) than pure CH 4 hydrate at geologically relevant temperatures. In this study, the conductivity was obtained from frequency-dependent impedance ( Z ) measurements made on polycrystalline CO 2 hydrate (CO 2 ·6.0 ± 0.2H 2 O by methods here) with 25% gas-filled porosity, compared with CH 4 hydrate (CH 4 ·5.9H 2 O) formed and measured in the same apparatus and exhibiting closely matching grain characteristics. The conductivity of CO 2 hydrate is 6.5 × 10 –4 S/m at 273K with an activation energy ( E a ) of 46.5 kJ/mol at 260–281 K, compared with ~5 × 10 –5 S/m and 34.8 kJ/m for CH 4 hydrate. Equivalent circuit modeling indicates that different pathways govern conduction in CO 2 versus CH 4 hydrate. Results show promise for use of electromagnetic methods in monitoring CO 2 hydrate formation in certain natural settings or in CO 2 /CH 4 exchange efforts.
58 GEOSCIENCES↗
Methane and Carbon Dioxide Fluxes in a Temperate Tidal Salt Marsh: Comparisons Between Plot and Ecosystem Measurements
Tidal wetlands are comprised of complex interdependent pathways where measurements of carbon exchange are often scale dependent. Common data collection methods (i.e., chambers and eddy covariance) are inherently constrained to different spatial and temporal scales which could generate biased information for applications of carbon accounting, identifying functional relationships and predicting future responses to climate change. Consequently, it is needed to systematically evaluate measurements derived from multiple approaches to identify differences and how techniques complement each other to reconcile interpretations. For our study, to accomplish this, we tested ecosystem-scale eddy covariance with plot-scale chamber measurements within a temperate salt marsh. We found good agreement (R 2 = 0.71–0.95) when comparing measurements of CH 4 emissions and CO 2 exchange but this agreement was dependent upon canopy phenology with discrepancies mainly arising during senescence and dormancy phenophases. The environmental drivers for CH 4 and CO 2 fluxes were mostly preserved across different measurement techniques, but the number of drivers increases while their individual strength decreases at the ecosystem scale. Empirical upscaling models parameterized with chamber measurements overestimated annual net ecosystem exchange (NEE; 108%) and gross primary production (GPP; 12%) while underestimating ecosystem respiration (Reco; 14%) and CH 4 emissions (69%) compared to eddy covariance measurements. Our results suggest that the environmental complexity of CH 4 and CO 2 fluxes in salt marshes may be underestimated by chamber-based measurements, and highlights how different techniques are complementary while considering limitations at each level of measurement.
54 ENVIRONMENTAL SCIENCES↗
Temporal Error Correlations in a Terrestrial Carbon Cycle Model Derived by Comparison to Carbon Dioxide Eddy Covariance Flux Tower Measurements
Abstract Atmospheric CO 2 flux inversions require as input an estimate of spatial and temporal correlations of errors in their estimate of the prior mean. Some previous studies have used the differences in CO 2 daily average flux estimates produced by terrestrial carbon cycle models and eddy covariance measurements to constrain the flux error correlations. Since inversions are starting to resolve the daily cycle, we set out to examine the correlations at sub‐daily time scales, as well as the correlations across years. To this end, we examine the autocorrelations in the difference between net ecosystem‐atmosphere exchange measurements from 75 AmeriFlux towers and temporally downscaled high‐spatial‐resolution flux estimates from the Carnegie‐Ames‐Stanford Approach (CASA) terrestrial carbon cycle model. We find that the daily cycle is prominent in these hourly autocorrelations and that these autocorrelations persist across years. We propose a family of functions to model these temporal correlations in atmospheric inversions, and use cross validation to determine which of the correlation functions best fits autocorrelation data from towers not in the training set. Correlation functions with a component that attempts to model the daily cycle in the differences match correlations from other towers better than those without. Those models that reproduce the same correlation structures at 1‐year intervals while modulating the amplitudes of the correlations between those intervals improve the fit still further.
54 ENVIRONMENTAL SCIENCES↗
Numerical Investigation of Observational Flux Partitioning Methods for Water Vapor and Carbon Dioxide
Abstract While yearly budgets of CO 2 flux (F c ) and evapotranspiration (ET) above vegetation can be readily obtained from eddy‐covariance measurements, the separate quantification of their soil (respiration and evaporation) and canopy (photosynthesis and transpiration) components remains an elusive yet critical research objective. In this work, we investigate four methods to partition observed total fluxes into soil and plant sources: two new and two existing approaches that are based solely on analysis of conventional high frequency eddy‐covariance (EC) data. The physical validity of the assumptions of all four methods, as well as their performance under different scenarios, are tested with the aid of large‐eddy simulations, which are used to replicate eddy‐covariance field experiments. Our results indicate that canopies with large, exposed soil patches increase the mixing and correlation of scalars; this negatively impacts the performance of the partitioning methods, all of which require some degree of uncorrelatedness between CO 2 and water vapor. In addition, best performances for all partitioning methods were found when all four flux components are non‐negligible, and measurements are collected close to the canopy top. Methods relying on the water‐use efficiency (W) perform better whenWis known a priori, but are shown to be very sensitive to uncertainties in this input variable especially when canopy fluxes dominate. We conclude by showing how the correlation coefficient between CO 2 and water vapor can be used to infer the reliability of differentWparameterizations.
Environmental Sciences & Ecology↗
Hydroxide promotes carbon dioxide electroreduction to ethanol on copper via tuning of adsorbed hydrogen
Producing liquid fuels such as ethanol from CO 2 , H 2 O, and renewable electricity offers a route to store sustainable energy. The search for efficient electrocatalysts for the CO 2 reduction reaction relies on tuning the adsorption strength of carbonaceous intermediates. Here, we report a complementary approach in which we utilize hydroxide and oxide doping of a catalyst surface to tune the adsorbed hydrogen on Cu. Density functional theory studies indicate that this doping accelerates water dissociation and changes the hydrogen adsorption energy on Cu. We synthesize and investigate a suite of metal-hydroxide-interface-doped-Cu catalysts, and find that the most efficient, Ce(OH) x -doped-Cu, exhibits an ethanol Faradaic efficiency of 43% and a partial current density of 128 mA cm -2 . Mechanistic studies, wherein we combine investigation of hydrogen evolution performance with the results of operando Raman spectroscopy, show that adsorbed hydrogen hydrogenates surface *HCCOH, a key intermediate whose fate determines branching to ethanol versus ethylene.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Bismuthene for highly efficient carbon dioxide electroreduction reaction
Bismuth (Bi) has been known as a highly efficient electrocatalyst for CO 2 reduction reaction. Stable free-standing two-dimensional Bi monolayer (Bismuthene) structures have been predicted theoretically, but never realized experimentally. Here, we show the first simple large-scale synthesis of free-standing Bismuthene, to our knowledge, and demonstrate its high electrocatalytic efficiency for formate (HCOO - ) formation from CO 2 reduction reaction. The catalytic performance is evident by the high Faradaic efficiency (99% at -580 mV vs. Reversible Hydrogen Electrode (RHE)), small onset overpotential (<90 mV) and high durability (no performance decay after 75 h and annealing at 400 °C). Density functional theory calculations show the structure-sensitivity of the CO2 reduction reaction over Bismuthene and thicker nanosheets, suggesting that selective formation of HCOO - indeed can proceed easily on Bismuthene (111) facet due to the unique compressive strain. This work paves the way for the extensive experimental investigation of Bismuthene in many different fields.
Science & Technology - Other Topics↗
A metal-supported single-atom catalytic site enables carbon dioxide hydrogenation
Nitrogen-doped graphene-supported single atoms convert CO 2 to CO, but fail to provide further hydrogenation to methane – a finding attributable to the weak adsorption of CO intermediates. To regulate the adsorption energy, here we investigate the metal-supported single atoms to enable CO 2 hydrogenation. We find a copper-supported iron-single-atom catalyst producing a high-rate methane. Density functional theory calculations and in-situ Raman spectroscopy show that the iron atoms attract surrounding intermediates and carry out hydrogenation to generate methane. The catalyst is realized by assembling iron phthalocyanine on the copper surface, followed by in-situ formation of single iron atoms during electrocatalysis, identified using operando X-ray absorption spectroscopy. The copper-supported iron-single-atom catalyst exhibits a CO 2 -to-methane Faradaic efficiency of 64% and a partial current density of 128 mA cm –2 , while the nitrogen-doped graphene-supported one produces only CO. The activity is 32 times higher than a pristine copper under the same conditions of electrolyte and bias.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electrochemically in situ formed rocksalt phase in titanium dioxide determines pseudocapacitive sodium-ion storage
Earth-abundant TiO 2 is a promising negative electrode for low-cost sodium-ion batteries (SIBs) owing to its high capacity, rapid (dis)charging capability, safe operation potential and nonflammability. Crystalline anatase TiO 2 is not suitable for reversible Na + (de)intercalation, but it displays pseudocapacitive response after repeated cycles. Herein, we find and demonstrate that ordered rocksalt (RS) NaTiO 2 nanograins are in situ formed by electrochemically cycling with Na + ions in anatase and amorphous TiO 2 . The in situ formed RS-NaTiO 2 follows a solid-solution reaction with small volume changes of only 2.0%, that determines the pseudocapacitive “mirror-like” cyclic voltammetry curve with a couple of broad redox peaks at 0.75 V vs. Na + /Na, a high capacity of 253 mAh g −1 , high-rate capability and thousands of stable cycles. The multistep crystalline-to-amorphous-to-RS transformations are able to be electrochemically activated during the aging process of assembled full cells. Our finding provides a direction for developing unconventional Ti-based high-performance active materials for SIBs with both high energy and power densities.
Tang, Dafu [Xiamen University (China); Innovation ↗
Molecular recognition and specificity of biomolecules to titanium dioxide from molecular dynamics simulations
Not Available
36 MATERIALS SCIENCE↗
Excitonic effects in absorption spectra of carbon dioxide reduction photocatalysts
Abstract The formation and disassociation of excitons play a crucial role in any photovoltaic or photocatalytic application. However, excitonic effects are seldom considered in materials discovery studies due to the monumental computational cost associated with the examination of these properties. Here, we study the excitonic properties of nearly 50 photocatalysts using state-of-the-art Bethe–Salpeter formalism. These ~50 materials were recently recognized as promising photocatalysts for CO 2 reduction through a data-driven screening of 68,860 materials. Here, we propose three screening criteria based on the optical properties of these materials, taking excitonic effects into account, to further down select six materials. Furthermore, we study the correlation between the exciton binding energies obtained from the Bethe–Salpeter formalism and those obtained from the computationally much less-expensive Wannier–Mott model for these chemically diverse ~50 materials. This work presents a paradigm towards the inclusion of excitonic effects in future materials discovery for solar-energy harvesting applications.
36 MATERIALS SCIENCE↗
Potential use of engineered nanoparticles in ocean fertilization for large-scale atmospheric carbon dioxide removal
Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration. AOF carbon sequestration efficiency appears lower than natural ocean fertilization processes due mainly to the low bioavailability of added nutrients, along with low export rates of AOF-produced biomass to the deep ocean. Here we explore the potential application of engineered nanoparticles (ENPs) to overcome these issues. Data from 123 studies show that some ENPs may enhance phytoplankton growth at concentrations below those likely to be toxic in marine ecosystems. ENPs may also increase bloom lifetime, boost phytoplankton aggregation and carbon export, and address secondary limiting factors in AOF. Life-cycle assessment and cost analyses suggest that net CO 2 capture is possible for iron, SiO 2 and Al 2 O 3 ENPs with costs of 2–5 times that of conventional AOF, whereas boosting AOF efficiency by ENPs should substantially enhance net CO 2 capture and reduce these costs. Therefore, ENP-based AOF can be an important component of the mitigation strategy to limit global warming.
54 ENVIRONMENTAL SCIENCES↗
Carbon dioxide-enhanced metal release from kerogen
Heavy metals released from kerogen to produced water during oil/gas extraction have caused major environmental concerns. To curtail water usage and production in an operation and to use the same process for carbon sequestration, supercritical CO 2 (scCO 2 ) has been suggested as a fracking fluid or an oil/gas recovery agent. It has been shown previously that injection of scCO 2 into a reservoir may cause several chemical and physical changes to the reservoir properties including pore surface wettability, gas sorption capacity, and transport properties. Using molecular dynamics simulations, we here demonstrate that injection of scCO 2 might lead to desorption of physically adsorbed metals from kerogen structures. This process on one hand may impact the quality of produced water. On the other hand, it may enhance metal recovery if this process is used for in-situ extraction of critical metals from shale or other organic carbon-rich formations such as coal.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗