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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Electrocatalytic CO 2 Reduction to Fuels: Progress and Opportunities

The electrochemical reduction of CO 2 continues to be an appealing option for storing renewable energy in a chemical form. In this review, we assess progress in designing catalysts that convert CO 2 to high energy density products. We explain how reaction data can be reported to reflect the intrinsic properties of the catalyst. This analysis shows that limited advances have been made in improving the performance of Cu. We suggest that opportunities remain using bimetallic catalysts that are resistant to dealloying. While aqueous systems are instrumental to developing our understanding of this chemistry, gas-fed systems that operate at high current densities must be developed. Although obstacles remain for practical application of CO 2 reduction, advances in fundamental understanding made over the years give reason for optimism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A trade-off between plant and soil carbon storage under elevated CO 2

Terrestrial ecosystems remove about 30 per cent of the carbon dioxide (CO 2 ) emitted by human activities each year, yet the persistence of this carbon sink depends partly on how plant biomass and soil organic carbon (SOC) stocks respond to future increases in atmospheric CO 2 . Although plant biomass often increases in elevated CO 2 (eCO 2 ) experiments, SOC has been observed to increase, remain unchanged or even decline. The mechanisms that drive this variation across experiments remain poorly understood, creating uncertainty in climate projections. In this study we synthesized data from 108 eCO 2 experiments and found that the effect of eCO 2 on SOC stocks is best explained by a negative relationship with plant biomass: when plant biomass is strongly stimulated by eCO 2 , SOC storage declines; conversely, when biomass is weakly stimulated, SOC storage increases. This trade-off appears to be related to plant nutrient acquisition, in which plants increase their biomass by mining the soil for nutrients, which decreases SOC storage. We found that, overall, SOC stocks increase with eCO 2 in grasslands (8 ± 2 per cent) but not in forests (0 ± 2 per cent), even though plant biomass in grasslands increase less (9 ± 3 per cent) than in forests (23 ± 2 per cent). Ecosystem models do not reproduce this trade-off, which implies that projections of SOC may need to be revised.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Quantification of CO 2 Mineralization at the Wallula Basalt Pilot Project

In 2013, the Pacific Northwest National Laboratory led a geologic carbon sequestration field demonstration where ~1000 tonnes of CO 2 was injected into several deep Columbia River Basalt zones near Wallula, Washington. Rock core samples extracted from the injection zone two years after CO 2 injection revealed nascent carbonate mineralization that was qualitatively consistent with expectations from laboratory experiments and reactive transport modeling. In this study, we report on a new detailed analysis of the 2012 pre-injection and 2015 post-injection hydrologic tests that capitalizes on the difference in fluid properties between scCO 2 and water to assess changes in near-field, wellbore, and reservoir conditions that are apparent approximately two years following the end of injection. This comparative hydrologic test analysis method provides a new way to quantify the amount of injected CO 2 that was mineralized in the field test. Modeling results indicate that approximately 60% of the injected CO 2 was sequestered via mineralization within two years, with the resulting carbonates occupying ~4% of the available reservoir pore space. The method presented here provides a new monitoring tool to assess the fate of CO 2 injected into chemically reactive basalt formations but could also be adapted for long-term monitoring and verification within more traditional subsurface carbon storage reservoirs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Improving productivity and stability for CO 2 hydrogenation by using pincer-ligated Mn complexes with hemilabile ligands

Pincer ligands are widely used to support transition metal catalysts, but first-row systems often deactivate too quickly for widespread use. Here, pincer ligands bearing an additional hemilabile donor were designed to stabilize Mn catalysts for CO 2 hydrogenation to formate. Ligands of the type (RCH 2 CH 2 )N(CH 2 CH 2 P i Pr 2 ) 2 ( iPr PN R P; R = OMe, CH 2 OMe, NMe 2 , P i Pr 2 ) were synthesized and coordinated to Mn to form complexes of the type ( iPr PN R P)Mn(CO) 2 H. Their performance was compared to {MeN(CH 2 CH 2 P i Pr 2 ) 2 }Mn(CO) 2 H, which lacks a pendant donor. The pendant donor identity and arm length strongly influenced catalytic activity, but all pendant arm containing systems extended catalyst lifetime. Notably, ( iPr PN CH2OMe P)Mn(CO) 2 H achieved turnover frequencies of 158,000 h -1 and turnover numbers of 838,000, exceeding most state-of-the-art catalysts. Mechanistic studies revealed that hemilabile coordination enhances stability by avoiding deactivation, although excessive binding can lead to inactive states. Here, this work demonstrates hemilabile donors dramatically improve pincer-based Mn catalysts and provides design principles for broader applications.

CO2 hydrogenation↗
DOE OSTI2025

Boosting Hydrogenation of CO 2 Using Cationic Cu Atomically Dispersed on 2D γ‐Al 2 O 3 Nanosheets

The continuous development of novel catalytic approaches is crucial for advancing efficient CO 2 hydrogenation processes. Drawing inspiration from single-atom catalysis and 2D materials, we designed a new 2D single-atom catalyst with excellent thermal stability by thermally treating Cu-adsorbed γ-AlOOH nanosheets, which yielded a Cu/γ-Al 2 O 3 catalyst with high activity in the hydrogenation of CO 2 -yielding methanol (CH 3 OH), dimethyl ether (DME), and CO as products. The active Cu sites are monodispersed and highly stable due to their cationic oxidation state and their substitution for pentacoordinated aluminum (Al P ) sites on particle surfaces. This study demonstrates an efficient approach for achieving a high CO 2 hydrogenation rate (30.45 mol mol −1 h −1 ) using a catalyst system that lacks metallic Cu centers, traditionally considered essential for H₂ dissociation, and employs what was previously thought to be an inert metal oxide (γ-Al 2 O 3 ) for CO and CH 3 OH production. Ongoing mechanistic studies aim to elucidate the synergy between cationic Cu single atoms and γ-Al 2 O 3 , a Lewis acid support, in facilitating hydrogen (H 2 ) activation and methanol formation.

2D catalyst↗
NASA NTRSDate not supplied

A Simulated High CO 2 Spaceflight Environment Increases Plant Preference for Ammonium as a Nitrogen Source

Long-duration exploration missions will require a sustainable supply of food to support human crews. The spaceflight environment contains high concentrations of CO 2 due to release by astronauts that cannot be completely scrubbed. It is therefore crucial to understand plant responses to elevated CO 2 (eCO 2 ) environments. Nitrogen (N) is crucial for plant survival, though the effects of eCO 2 on plant N uptake remain poorly understood. Shoot nitrate reduction may be reduced at eCO 2 , due to reduced reductant availability for nitrate reduction due to reduced photorespiration and increased carbon fixation. Relative growth rate may be reduced at eCO 2 when N is provided only as nitrate and can be unaffected when N is supplied as ammonium, suggesting eCO 2 may drive increased plant ‘preference’ for ammonium. However, changes in N preference in response to eCO 2 have, to our knowledge, not yet been studied. In this study, novel stable isotope approaches were used in conjunction with hydroponics and isotope ratio mass spectrometry to determine the effect of space station-like eCO 2 (3000 ppm) on preference for ammonium or nitrate in several lettuce varieties previously grown in space, when both N forms are provided equally. All varieties displayed significant ammonium preference irrespective of CO 2 concentration, however the extent of this preference varied. Increased ammonium preference was observed for all varieties at eCO 2 compared to ambient CO 2 (410 ppm), driven by increases in nitrogen uptake which plants disproportionately took up as ammonium. These results suggest that future nutrient formulations should favor ammonium as a major N source for space crop production. Moreover, increased ammonium preference may play a role in future plant-based bioregenerative life support systems with higher ammonium concentrations due to waste recycling. Additionally, this research furthers our understanding of plant responses to future high CO 2 climates, allowing the development of future-proof crops to maintain food security.

space crop production↗
DOE OSTI2023

Cost of Capturing CO 2 from Industrial Sources

The objective of this study is to provide an estimate of the cost to capture carbon dioxide (CO 2 ) from select industrial processes (ammonia, ethylene oxide, ethanol, natural gas processing, coal-to-liquids, gas-to-liquids, refinery hydrogen, cement, iron/steel, and pulp/paper). Each of the ten processes were chosen for analysis due to either the high purity of the CO 2 emission source (99–100 mole percent CO 2 ) or the large quantity of CO 2 potentially available. For each industrial process considered, available plant information, such as existing average plant size, projected new development plant size, or existing plant operations data was used to develop a reference plant for this study.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2022

Superior CO 2 /N 2 separation performance of highly branched Poly(1,3 dioxolane) plasticized by polyethylene glycol

With its high content of CO 2 -philic ether oxygen groups, poly(1,3-dioxolane) (PDXLA) has emerged as an attractive platform to achieve excellent CO 2 /N 2 separation properties for post-combustion carbon capture. Herein we demonstrate that the separation properties of PDXLA can be further enhanced by plasticizing with miscible polyethylene glycol (PEG)-based additives using an integrated experimentation and modeling approach. The effects of the chain end groups and loading level of the additives on the physical properties of the blends are thoroughly investigated, including glass transition temperature (T g ), fractional free volume, and gas transport properties, and the effects can be satisfactorily described using models available for homogeneous blends. Notably, a T g -integrated free volume model is adapted to successfully interpret the unified effect of the blend composition and temperature on gas diffusivity and permeability. A sample containing 45 mass% PEG dimethyl ether (PEGDME with a molecular mass of 240 g/mol) displays stable mixed-gas CO 2 permeability of 1540 Barrer and CO 2 /N 2 selectivity of 40 when challenged with a model flue gas at 60 °C, outperforming Robeson's 2008 upper bound. Elucidating how small plasticizers impact gas transport in homogeneous blends may unravel a facile way to design high-performance membranes for gas separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Unsteady- and Steady-State Relative Permeability Study with X-ray and Acoustic Monitoring for CO 2 Storage in Deep Saline Aquifers

In this study, we link the multiphase flow measurements with controls of sedimentary structures (e.g., heterogeneity and anisotropy) on relative permeability to variations in ultrasonic velocities for two deep saline aquifer formations (Entrada and Bluff Sandstones) in the San Juan Basin of the Southwestern USA. The rock specimens were extracted from outcrop sites near Durango, CO, USA. They have distinct differences in grain size, cementation composition, and individual chemical amounts, despite both formations being eolian sandstones. We performed a series of unsteady- and steady-state CO 2 -brine relative permeability experiments under capillary-controlled displacement rates. Unsteady-state experiments were conducted at 71 °C and 9.65 MPa; steady-state experiments were conducted at 85 °C and 22.8 MPa and 89 °C and 24.1 MPa for the Bluff and Entrada Sandstones, respectively. During the unsteady experiments, X-ray computed tomography was used to visualize multiphase flow in porous media and quantify saturations during brine drainage under various flow rates. Scan images and saturation profiles indicate that the CO 2 distribution in the pore volume was strongly impacted by the presence of high-angle cross-laminations, heterogeneous rock structure, and direction of bedding orientation. Those factors contribute to dramatic and quick initial breakthroughs and affect the overall saturation dynamics. Steady-state relative permeability tests were conducted at net flow rates of 1 mL/min for both brine drainage and imbibition. During the experimental steps, the CO 2 fractional flow was increased and decreased for both drainage and imbibition scenarios to mimic the front when CO 2 contacts brine and behind the front when brine enters space previously occupied by CO 2 . It was found that compressional velocity decreased, while shear waves slightly increased as brine saturation decreased. The hysteresis effects for the relative permeability and acoustic velocities were distinct. Furthermore, the CO 2 /brine front stability is quantified by applying a mobility ratio approach to spot saturations at which the boundary line between fluids becomes uneven. The results presented in this work can potentially boost the quality and precision of forecasts for the CO 2 storage projects in which the vertical and horizontal core-scale heterogeneity and anisotropy impact the plume migration within host reservoirs.

carbon dioxide (CO2)↗
DOE OSTI2023

Root and Microbial Soil CO 2 and CH 4 Fluxes Respond Differently to Seasonal and Episodic Environmental Changes in a Temperate Forest

Upland forest soils are typically major atmospheric carbon dioxide (CO 2 ) sources and methane (CH 4 ) sinks, but the contributions of root and microbial processes, as well as their separate temporal responses to environmental change, remain poorly understood. This 2-year study was conducted in a temperate, deciduous forest located on the Chesapeake Bay in Maryland, USA. We used temporal CO 2 and CH 4 flux measurements, exclusion-source partitioning, and an ecosystem-scale flooding experiment to understand how carbon (C) fluxes, and their root and microbial sources, respond to seasonal and episodic environmental change. Here, we show that the root-and-rhizosphere component of soil CO 2 and CH 4 flux is significant and that its dependence on soil temperature and volumetric water content (VWC) influences soil C dynamics at seasonal timescales. Experimental flooding shows that CO 2 and CH 4 flux responses to episodic moisture change were driven by suppression of soil heterotrophs, while root respiration did not respond to transient hydrologic disturbance. Methane uptake responded strongly to episodic inundation, reinforcing the important role of soil moisture in the short-term control of the forest soil CH 4 sink. However, despite the clear seasonality of CH 4 uptake, as well as its strong response to short-term experimental inundation, temperature and VWC were weak predictors of CH 4 uptake at a seasonal timescale. We suggest that CH 4 consumption in the long-term may be determined by vegetation, nutrients, microbial communities, or other factors correlated with seasonal changes. Our results indicate that root and microbial sources of both CO 2 and CH 4 flux respond differently in timing and magnitude to seasonal and episodic environmental change.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Directing CO 2 electroreduction pathways for selective C 2 product formation using single-site doped copper catalysts

Manipulating the selectivity-determining step in post-C–C coupling is crucial for enhancing C 2 product specificity during electrocatalytic CO 2 reduction, complementing efforts to boost rate-determining step kinetics. Here we highlight the role of single-site noble metal dopants on Cu surfaces in influencing C–O bond dissociation in an oxygen-bound selectivity-determining intermediate, steering post-C–C coupling toward ethylene versus ethanol. Integrating theoretical and experimental analyses, we demonstrate that the oxygen binding strength of the Cu surface controls the favorability of C–O bond scission, thus tuning the selectivity ratio of ethylene-to-ethanol. The Rh-doped Cu catalyst with optimal oxygen binding energy achieves a Faradaic efficiency toward ethylene of 61.2% and an ethylene-to-ethanol Faradaic efficiency ratio of 4.51 at –0.66 V versus RHE (reversible hydrogen electrode). Integrating control of both rate-determining and selectivity-determining steps further raises ethylene Faradaic efficiency to 68.8% at 1.47 A cm -2 in a tandem electrode. Our insights guide the rational design of Cu-based catalysts for selective CO 2 electroreduction to a single C 2 product.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Quantifying the Potential Atmospheric Leakage Risks Associated With the Geologic Storage of CO 2 in Saline Aquifers for Use in Voluntary Carbon Market Buffer Account Determination

Conference paper presented at 17th International Conference on Greenhouse Gas Control Technologies (GHGT-17), Calgary, Alberta, Canada, October 20–24, 2024. This paper presents the results of a detailed study into the potential atmospheric leakage risks associated with the geologic storage of CO 2 in saline aquifers. This study included a detailed literature review, a re-creation of existing CO 2 leakage models put forth by other authors and, lastly, the development of an enhanced model that can be utilized for assessing the potential losses to the atmosphere of stored CO 2 across a variety of potential project parameters. The results of this study indicate that, across broad ranges of input parameters for mechanisms that have the potential for CO 2 loss from the storage complex to the atmosphere, there is an extremely low risk of CO 2 leakage to the atmosphere, with the median leakage risk estimated to be 0.1% of total injected CO 2 . The risk of leakage from real-world storage projects is likely to be even lower than those estimated through this study.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2021

Scalable fabrication of high activity nanoporous copper powders for electrochemical CO 2 reduction via ball milling and dealloying

Electrochemical CO 2 reduction (ECR) is a promising technology to close the anthropic CO 2 circle using renewable energy to achieve carbon neutrality. Future commercialization of ECR will require the development of new catalyst synthesis routes that will allow significant upscaling of catalyst production from current research-level milligram quantities to the kilogram scale and beyond while maintaining the activity and selectivity demonstrated at the research level. Here, we report on generating and testing submicron-sized nanoporous copper (npCu) particles by using a scalable approach consisting of ball milling brittle Cu-based intermetallics followed by dealloying to add nanoporosity for high surface area. The resulting npCu particles have been tested in an industry-relevant large area (25 cm 2 ) electrolyzer platform and showed Faraday efficiencies (FE) for ethylene up to 34 % at current densities of 75–100 mA/cm 2 while keeping FE for hydrogen less than 30 %. Our results demonstrate that a combination of ball milling and dealloying is a promising approach to generate large quantities of high activity and high surface area npCu particles for ECR at an industry-relevant scale.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Species interactions amplify functional group responses to elevated CO 2 and N enrichment in a 24‐year grassland experiment

Abstract Plant functional groups (FGs) differ in their response to global changes, although species within those groups also vary in such responses. Both species and FG responses to global change are likely influenced by species interactions such as inter‐specific competition and facilitation, which are prevalent in species mixtures but not monocultures. As most studies focus on responses of plants growing in either monocultures or mixtures, but rarely both, it remains unclear how interspecific interactions in diverse ecological communities, especially among species in different FGs, modify FG responses to global changes. To address these issues, we leveraged data from a 16‐species, 24‐year perennial grassland experiment to examine plant FG biomass responses to atmospheric CO 2 , and N inputs at different planted diversity. FGs differed in their responses to N and CO 2 treatments in monocultures. Such differences were amplified in mixtures, where N enrichment strongly increased C3 grass success at ambient CO 2 and C4 grass success at elevated CO 2 . Legumes declined with N enrichment in mixtures at both CO 2 levels and increased with elevated CO 2 in the initial years of the experiment. Our results suggest that previous studies that considered responses to global changes in monocultures may underestimate biomass changes in diverse communities where interspecific interactions can amplify responses. Such effects of interspecific interactions on responses of FGs to global change may impact community composition over time and consequently influence ecosystem functions.

Mohanbabu, Neha↗
DOE OSTI2022

The ABCflux database: Arctic–boreal CO 2 flux observations and ancillary information aggregated to monthly time steps across terrestrial ecosystems

Past efforts to synthesize and quantify the magnitude and change in carbon dioxide (CO 2 ) fluxes in terrestrial ecosystems across the rapidly warming Arctic–boreal zone (ABZ) have provided valuable information but were limited in their geographical and temporal coverage. Furthermore, these efforts have been based on data aggregated over varying time periods, often with only minimal site ancillary data, thus limiting their potential to be used in large-scale carbon budget assessments. To bridge these gaps, we developed a standardized monthly database of Arctic–boreal CO 2 fluxes (ABCflux) that aggregates in situ measurements of terrestrial net ecosystem CO 2 exchange and its derived partitioned component fluxes: gross primary productivity and ecosystem respiration. The data span from 1989 to 2020 with over 70 supporting variables that describe key site conditions (e.g., vegetation and disturbance type), micrometeorological and environmental measurements (e.g., air and soil temperatures), and flux measurement techniques. Here, we describe these variables, the spatial and temporal distribution of observations, the main strengths and limitations of the database, and the potential research opportunities it enables. In total, ABCflux includes 244 sites and 6309 monthly observations; 136 sites and 2217 monthly observations represent tundra, and 108 sites and 4092 observations represent the boreal biome. The database includes fluxes estimated with chamber (19 % of the monthly observations), snow diffusion (3 %) and eddy covariance (78 %) techniques. The largest number of observations were collected during the climatological summer (June–August; 32 %), and fewer observations were available for autumn (September–October; 25 %), winter (December–February; 18 %), and spring (March–May; 25 %). ABCflux can be used in a wide array of empirical, remote sensing and modeling studies to improve understanding of the regional and temporal variability in CO 2 fluxes and to better estimate the terrestrial ABZ CO 2 budget.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Low-frequency electrochemical pulsing to manage flooding and salt precipitation in zero-gap CO 2 -to-ethylene electrolyzers

The electrochemical reduction of carbon dioxide (CO 2 ) to ethylene presents a promising route for utilizing exhaust gases to produce value-added chemicals with broad manufacturing applications. While zero-gap electrolyzer architectures show great potential to enable commercial-scale CO 2 -to-ethylene conversion, their performance is often limited by failure within the first 100 hours. In this work, we demonstrate that a low-frequency electrochemical pulsing protocol effectively mitigates carbonate salt precipitation and flooding by managing water transport to and through the cathode gas diffusion electrode and associated flow fields. Operando neutron imaging further reveals the dynamics of water crossover and flooding, emphasizing the intricate interplay between electrochemical operation and ionic transport. By mitigating short-term flooding and salt precipitation failure modes, this study establishes a foundation for understanding long-term degradation mechanisms and advancing the practical viability of CO 2 electrolyzers for industrial-scale applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Evaluating CCS Cost Options for CO 2 Sources in the Central United States

Carbon capture and storage (CCS) is considered one of many emerging strategies essential in the global effort to meet the dual challenge of providing affordable and reliable energy while addressing rising greenhouse gas emissions, particularly anthropogenic emissions of carbon dioxide (CO 2 ) into the atmosphere. The Central United States has an abundance of CO 2 -generating sources that would likely require tailored approaches to CO 2 management. This analysis divided the Central United States into three regional impact areas to explore options a CO 2 source faces when transporting and storing its captured CO 2 .

54 ENVIRONMENTAL SCIENCES↗