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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effects of Anion Identity and Concentration on Electrochemical Reduction of CO 2

The electrochemical reduction of CO 2 is known to be influenced by the concentration and identity of the anionic species in the electrolyte; however, a full understanding of this phenomenon has not been developed. Here, we present the results of experimental and computational studies aimed at understanding the role of electrolyte anions on the reduction of CO 2 over Cu surfaces. Experimental studies were performed to show the effects of bicarbonate buffer concentration and the composition of other buffering anions on the partial currents of the major products formed by reduction of CO 2 over Cu. It was demonstrated that the composition and concentration of electrolyte anions has relatively little effect on the formation of CO, HCOO - , C 2 H 4 , and CH 3 CH 2 OH, but has a significant effect on the formation of H 2 and CH 4 . Continuum modeling was used to assess the effects of buffering anions on the pH at the electrode surface. The influence of pH on the activity of Cu for producing H 2 and CH 4 was also considered. Changes in the pH near the electrode surface were insufficient to explain the differences in activity and selectivity observed with changes in anion buffering capacity observed for the formation of H 2 and CH 4 . Therefore, it is proposed that these differences are the result of the ability of buffering anions to donate hydrogen directly to the electrode surface and in competition with water. The effectiveness of buffering anions to serve as hydrogen donors is found to increase with decreasing p K a of the buffering anion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Hybrid Carbon Dioxide Reduction Photocatalysts Consisting of Macrocyclic Cobalt(III) Complexes Deposited on Semiconductor Surfaces

Hybrid photocatalysts can be prepared by coupling metal ligand complexes with light-harvesting semiconductors. It is often challenging and time consuming to derivatize ligands with anchoring groups to effectively attach onto surfaces. In this study, we synthesized hybrid carbon dioxide reduction photocatalysts by directly depositing two macrocyclic Co(III) complexes on three different semiconductor surfaces (TiO 2 , N-Ta 2 O 5 and C 3 N 4 ). The resulting hybrid photocatalysts were characterized with various techniques and tested in CO 2 reduction reactions under different light conditions. Excellent visible-light CO 2 -reduction activity was obtained using C 3 N 4 as the light-harvesting semiconductor. Furthermore, density functional theory calculations were conducted to help understand interactions between the cobalt complexes with a model TiO 2 surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Electrocatalytic CO 2 Reduction with a Ruthenium Catalyst in Solution and on Nanocrystalline TiO 2

A Ru II complex [Ru(PO 3 Et 2 -ph-tpy)(6-mbpy)(NCCH 3 )] 2+ [PO 3 Et 2 -ph-tpy=diethyl(4-[(2,2':6',2"-terpyridin)-4'-yl]phenyl)phosphonate; 6-mbpy=6-methyl-2,2'-bipyridine] is explored as a molecular catalyst for electrocatalytic CO 2 reduction in both a homogeneous solution and, as a phosphonated derivative, on nanocrystalline-TiO 2 surfaces. In CH 3 CN, the complex acts as a selective electrocatalyst for reduction of CO 2 to CO at a low overpotential of 340 mV but with a limited turnover number (TON). An enhancement in reactivity was observed by immobilizing the phosphonated derivative of the catalyst on a nanocrystalline-TiO 2 electrode surface, with the catalyst surface protected by a thin overlayer of NiO. The surface-functionalized electrode was characterized by X-ray photoelectron and diffuse reflectance spectroscopies (XPS and DRS). Electrocatalytic reduction of CO 2 to CO occurred at -1.65 V versus Fc +/0 with a TON of 237 per catalyst site during 4 h of electrocatalysis. Post-catalysis XPS measurements reveal that the molecular structure of the catalyst is retained on TiO 2 after the long-term electrocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Heterogeneous Nature of Electrocatalytic CO/CO 2 Reduction by Cobalt Phthalocyanines

Molecular catalysts for electrochemical CO 2 reduction have traditionally been studied in their dissolved states. However, the heterogenization of molecular catalysts has the potential to deliver much higher reaction rates and enable the reduction of CO 2 by more than two electrons. In light of the recently discovered reactivity of heterogenized cobalt phthalocyanine molecules to catalyze CO 2 reduction into methanol, direct comparison is needed to uncover the distinct catalytic activity and selectivity in homogeneous catalysis versus heterogeneous catalysis. In this work, soluble cobalt phthalocyanine derivatives were synthesized, and their catalytic activities in the homogeneous solutions were evaluated. The results show that the observed catalytic activities for both CO 2 -to-CO and CO-to-methanol conversions in aqueous solutions of the cobalt phthalocyanines are predominantly heterogeneous in nature through the adsorbed species on the electrode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The pH and Potential Dependence of Pb–Catalyzed Electrochemical CO 2 Reduction to Methyl Formate in a Dual Methanol/Water Electrolyte

The conversion of waste CO 2 to value-added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of non-aqueous solvents like methanol allows for higher CO 2 availability and novel products. In this work, the electrochemistry of CO 2 reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half-reaction. The selectivity among methyl formate (a product unique to reduction of CO 2 in methanol), formic acid, and formate was critically dependent on the catholyte pH, with higher pH conditions leading to formate and low pH favoring methyl formate. Furthermore, the potential dependence of the product distribution in acidic catholyte was also investigated, with a faradaic efficiency for methyl formate as high as 75% measured at -2.0 V vs Ag/AgCl.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Tuning Structural and Electronic Configuration of FeN 4 via External S for Enhanced Oxygen Reduction Reaction

The Fe–N–C material represents an attractive oxygen reduction reaction electrocatalyst, and the FeN 4 moiety has been identified as a very competitive catalytic active site. Fine tuning of the coordination structure of FeN 4 has an essential impact on the catalytic performance. Herein, we construct a sulfur‐modified Fe–N–C catalyst with controllable local coordination environment, where the Fe is coordinated with four in‐plane N and an axial external S. The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN 4 active site. The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons. With the above characteristics, the adsorption and desorption of the reactants at FeN 4 active sites are optimized, thus promoting the oxygen reduction reaction activity. This work explores the key point in electronic configuration and coordination environment tuning of FeN 4 through S doping and provides new insight into the construction of M–N–C‐based oxygen reduction reaction catalysts.

25 ENERGY STORAGE↗
DOE OSTI2014

Electrochemical Measurement of Gold Oxide Reduction and Methods for Acid Neutralization and Minimization of Water in Wet Ionic Liquid

The formation and reduction of gold oxide in wet ionic liquid (IL), N-trimethyl-N-butylammonium bis(trifluoromethanesulfonyl)imide, ([Me 3 N n Bu][TFSI]) is examined. The water concentration is determined using both the charge and peak current from the reduction of gold oxide and compared directly with Karl Fischer data. The quantitative determination of water in the IL is demonstrated for concentrations between 0.09 and 0.74 by weight (w%). The treatment of wet IL with dry nitrogen or molecular sieves reduces the water below background levels. Finally, methods for acid neutralization and the reduction of water with molecular sieves are conducted to minimize their impact on subsequent electrochemical measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Modeling of the Reduction of Hematite in the Chemical Looping Combustion of Methane using Barracuda

Chemical looping combustion is a promising technology for the capture of CO 2 involving reduction and oxidation of materials known as oxygen carriers. One particular carrier is hematite as it is readily available and relatively inexpensive as well as being non-toxic. The objective of this paper is to present a new particle model and reaction kinetics that can be applied to Barracuda® simulations of the fuel reactor. This was done since Barracuda does not allow for the JMA (nucleation and growth) type kinetics that were developed from analytical study the results from TGA and fixed bed experiments. This paper summarizes the analytical analysis of the fixed bed reduction experiments conducted in a cycling fixed bed reactor and subsequently modeled with Barracuda® CFD software to develop the new model. The experiments were conducted using nominally 1000 g of hematite material. The cyclic processing began with the reduction step then proceeded to the oxidation step repeating this analysis for several cycles (5 to 10). The effects of fuel partial pressure (8.4, 7.2 and 5 mole %) on the conversion were investigated. The JMA analysis assumed the reactions to occur in the shell surrounding the particle grains with diffusion of oxygen to the grain surface from the core. In contrast, working with the particle kinetics allowed in Barracuda®, the reactions occur with different hematite species (surface and core) homogeneously mixed. Therefore it is necessary to develop a new particle model with the rates being related to the amount of reactant (surface or core) in the particle. This paper presents the development of such a particle model and compares the results with experimental results.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2023

The Reductive Leaching of Chalcopyrite by Chromium(II) Chloride for the Rapid and Complete Extraction of Copper

A hydrometallurgical process is developed to lower the costs of copper production and thereby sustain the use of copper throughout the global transition to renewable energy technologies. The unique feature of the hydrometallurgical process is the reductive treatment of chalcopyrite, which is in contrast to the oxidative treatment more commonly pursued in the literature. Chalcopyrite reduction by chromium(II) ion is described for the first time and superior kinetics are shown. At high concentrate loadings of 39, 78, and 117 gL –1 , chalcopyrite reacted completely within minutes at room temperature and pressure. The XRD, SEM-EDS, and XPS measurements indicate that chalcopyrite reacts to form copper(I) chloride (CuCl). After the reductive treatment, the mineral products are leached by iron(III) sulfate to demonstrate the complete extraction of copper. The chromium(II) ion may be regenerated by an electrolysis unit inspired by an iron chromium flow battery in a practical industrial process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Brief Review of Metallothermic Reduction Reactions for Materials Preparation

Metallothermic reduction reactions (MRRs) are displacement reactions that use reactive metals to reduce compounds so that metals, alloys, nonmetal elementary substances, and composites are produced, often in a scalable manner. In recent years, nonmetal materials, mainly silicon and carbon, particularly in their nanostructured forms obtained using an MRR with magnesium as the reductant, have started to attract much attention. However, reactions using other metals as the reductant have not been widely investigated yet. Furthermore, the reaction mechanisms and their controlling factors remain unclear, and much more effort is needed to advance this emerging field. Here, MRR preparation methods for metals, alloys, nanoporous silicon, nanoporous carbon, and composites are discussed as an introduction for new researchers in this field.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Wind power costs driven by innovation and experience with further reductions on the horizon

The costs of wind power have declined to levels on par with or below those of conventional sources in many parts of the world. Wind power has become one of the fastest-growing sources of new electricity generation. We take stock of wind power cost evolution over the past 20 years, review methodologies commonly used for cost assessment, discuss the potential for continued cost reduction, and identify anticipated cost and value drivers. Our scope includes both onshore and offshore wind technologies. We draw from a vast body of literature on these topics to highlight key trends, approaches, and limitations. Furthermore, we discuss strategies for wind power assets to enhance their marginal economic value to the broader power system and consumers. We identify a myriad of factors that are expected to influence the future cost and value of wind power, including siting, project scale, turbine size, operational synergies, commodity prices, advancements in turbine technologies, enhanced management of the wind resource, and novel control technologies that provide value for the electricity grid. Because the common methods for forecasting future costs each have their own strengths and weaknesses, we find the best insights are elicited from a combination of methods. Overall, researchers and analysts anticipate further sizable cost reductions for onshore and offshore wind. Midrange forecasts for levelized cost of energy in 2050 are generally between $20 and $30/MWh for onshore wind and $40 and $60/MWh for offshore wind, a reduction to approximately half of today's levels. Optimistic forecasts anticipate these levels as early as 2030.

17 WIND ENERGY↗
DOE OSTI2022

Maintaining Trust in Reduction: Preserving the Accuracy of Quantities of Interest for Lossy Compression

As the growth of data sizes continues to outpace computational resources, there is a pressing need for data reduction techniques that can significantly reduce the amount of data and quantify the error incurred in compression. Compressing scientific data presents many challenges for reduction techniques since it is often on non-uniform or unstructured meshes, is from a high-dimensional space, and has many Quantities of Interests (QoIs) that need to be preserved. To illustrate these challenges, we focus on data from a large scale fusion code, XGC. XGC uses a Particle-In-Cell (PIC) technique which generates hundreds of PetaBytes (PBs) of data a day, from thousands of timesteps. XGC uses an unstructured mesh, and needs to compute many QoIs from the raw data, f.One critical aspect of the reduction is that we need to ensure that QoIs derived from the data (density, temperature, flux surface averaged momentums, etc.) maintain a relative high accuracy. We show that by compressing XGC data on the high-dimensional, nonuniform grid on which the data is defined, and adaptively quantizing the decomposed coefficients based on the characteristics of the QoIs, the compression ratios at various error tolerances obtained using a multilevel compressor (MGARD) increases more than ten times. We then present how to mathematically guarantee that the accuracy of the QoIs computed from the reduced f is preserved during the compression. We show that the error in the XGC density can be kept under a user-specified tolerance over 1000 timesteps of simulation using the mathematical QoI error control theory of MGARD, whereas traditional error control on the data to be reduced does not guarantee the accuracy of the QoIs.

Gong, Qian↗
DOE OSTI2018

Gauged six-dimensional supergravity from warped IIB reductions

We find a family of complete non-linear Kaluza-Klein reduction ansätze from type IIB supergravity to Romans’ 6D F (4) gauged supergravity in the bosonic sector. The reduction is over a sphere S 2 and a Riemann surface Σ, and depends on a pair of arbitrary locally holomorphic functions A ± on Σ. This family of reductions is inspired by the recent construction of 1/2 BPS supersymmetric warped AdS 6 solutions of IIB supergravity that depend on these same functions A ± .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Potential for Methanosarcina to Contribute to Uranium Reduction during Acetate-Promoted Groundwater Bioremediation

Previous studies of acetate-promoted bioremediation of uranium-contaminated aquifers focused on Geobacter because no other microorganisms that can couple the oxidation of acetate with U(VI) reduction had been detected in situ. Monitoring the levels of methyl CoM reductase subunit A (mcrA) transcripts during an acetate-injection field experiment demonstrated that acetoclastic methanogens from the genus Methanosarcina were enriched after 40 days of acetate amendment. The increased abundance of Methanosarcina corresponded with an accumulation of methane in the groundwater. In order to determine whether Methanosarcina species could be participating in U(VI) reduction in the subsurface, cell suspensions of Methanosarcina barkeri were incubated in the presence of U(VI) with acetate provided as the electron donor. U(VI) was reduced by metabolically active M. barkeri cells; however, no U(VI) reduction was observed in inactive controls. These results demonstrate that Methanosarcina species could play an important role in the long-term bioremediation of uranium-contaminated aquifers after depletion of Fe(III) oxides limits the growth of Geobacter species. The results also suggest that Methanosarcina have the potential to influence uranium geochemistry in a diversity of anaerobic sedimentary environments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Patient Radiation Dose Reduction Considerations in a Contemporary Interventional Radiology Suite

PurposeWe sought to evaluate patient radiation exposure during complex liver interventional procedures performed with newer angiography equipment.Materials and MethodsWe conducted a retrospective study of transjugular intrahepatic portosystemic shunt (TIPS) creations and liver tumor embolizations performed in our new angiography suite (Discovery IGS740, GE Healthcare). T tests were used to compare air kerma-area product (P{sub KA}) and reference plane air kerma (K{sub a,r}) in the new room versus data from historical rooms and previous studies (including the RAD IR study). Results were expressed as medians [interquartile ranges (Q1, Q3)].ResultsFrom February 2015 to June 2016, 134 complex liver interventional procedures were performed in the new room, including 14 TIPS creations, 60 hepatic tumor arterial embolizations (HAEs), 26 Y90 mappings (Y90m), and 34 Y90 radioembolizations (Y90). K{sub a,r} (Gy) values were as follows: TIPS, 0.65 (0.24, 1.15); HAE, 0.89 (0.49, 1.49); Y90m, 0.54 (0.38, 0.94); Y90, 0.46 (0.21, 1.06). P{sub KA} (Gy·cm{sup 2}) values were as follows: TIPS, 148.2 (66.7, 326.5); HAE, 142.6 (88, 217.8); Y90m, 148.3 (98.2, 247); Y90, 90.8 (43.9, 161.5). K{sub a,r} and P{sub KA} were lower in the new room than in historical rooms [K{sub a,r} and P{sub KA} reductions: TIPS, 58 and 49%; HAE, 31 and 39%; Y90m, 58 and 52%; Y90, 49 and 56% (p < 0.05)] and versus the RAD IR study [K{sub a,r} and P{sub KA} reductions: TIPS, 64 and 43%; HAE, 26 and 40% (p < 0.05)].ConclusionsUsing the latest technology and image processing tools enables significant reduction in radiation exposure during complex liver interventional procedures.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Model reduction for fractured porous media: a machine learning approach for identifying main flow pathways

Discrete fracture networks (DFN) are often used to model flow and transport in fractured porous media. The accurate resolution of flow and transport behavior on a large DFN involving thousands of fractures is computationally expensive. This makes uncertainty quantification studies of quantities of interest such as travel time through the network computationally intractable, since hundreds to thousands of runs of the DFN model are required to get bounds on the uncertainty of the predictions. Prior works on the subject demonstrated that the complexity of a DFN could be reduced by considering a sub-network of it (often termed a “backbone” sub-network), one whose flow and transport properties were then shown to be similar to that of the full network. The technique is tantamount to partitioning the complete set of fractures of a network into two disjoint sets, one of which is the backbone sub-network while the other its complement. It is in this context that we present a system-reduction technique for DFNs using supervised machine learning via a Random Forest Classifier that selects a backbone sub-network from the full set of fractures. The in-sample errors (in terms of precision and recall scores) of the trained classifier are found to be very accurate indicators of the out-of-sample errors, thus exhibiting that the classifier generalizes well to test data. Moreover, this system-reduction technique yields sub-networks as small as 12% of the full DFN that still recover transport characteristics of the full network such as the peak dosage and tailing behavior for late times. Most importantly, the sub-networks remain connected, and their size can be controlled by a single dimensionless parameter. Furthermore, measures of KL-divergence and KS-statistic for the breakthrough curves of the sub-networks with respect to the full network show physically realistic trends in that the measures decrease monotonically as the size of the sub-networks increase. In conclusion, the computational efficiency gained by this technique depends on the size of the sub-network, but large reductions in computational time can be expected for small sub-networks, yielding as much as 90% computational savings for sub-networks that are as small as 10-12% of the full network.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Effect of Initial FeO Content and CaO:SiO{sub 2} Ratio on the Reduction Smelting Kinetics of the CaO-SiO{sub 2}-MgO{sub satd.}-FeO Slag System

The effect of the initial FeO content and CaO:SiO{sub 2} ratio (CaO mass pct/SiO{sub 2} mass pct) on the reduction smelting of FeO with carbon flake addition is investigated in the CaO-MgO{sub satd.}-SiO{sub 2}-FeO slag system at 1823 K (1550 °C). Carbon rapidly reacted with FeO in the molten slag, causing both foaming and compositional changes in the slag. As FeO is reduced, the MgO saturation is modified, and solid precipitants, including MgO and other complex oxides, were observed, which significantly affected the slag properties, including the viscosity and foaming behavior. The solid-phase fraction and viscosity were estimated from changes in the measured FeO content over time using the thermochemical software FactSage. The iron recovery, which is distinguished from the amount of reduced Fe droplets, showed opposite behavior to the measured maximum foaming height and modified foaming index. According to the FeO mass transfer coefficient considering slag foaming at various initial FeO contents and CaO:SiO{sub 2} ratios, the reduction rate was optimal at higher initial FeO contents and a CaO:SiO{sub 2} ratio of 2.0, which did not correspond to the optimal iron recovery at an initial FeO content of 44 mass pct and above and a CaO:SiO{sub 2} ratio of 1.2. The results showed that slag foaming may increase the reduction kinetics, but the slag composition needs to be optimized for greater iron recovery.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Reduction Mechanism of Iron Oxide Briquettes by Carbonaceous Materials Extracted from Blast Furnace Dust

The reducibility of carbonaceous powder extracted from blast furnace dust was investigated. In this study, pickling treatment was used for BF bag dust and BF gravitational dust to extract the carbonaceous material. The structural characteristics of carbonaceous material were studied by X-ray diffraction, scanning electron microscope, and energy-dispersive spectrometer. The reduction of ferric oxide and carbon gasification experiments were researched by thermogravimetry. The results show that the pickled raw coal gives the highest reducibility, which is followed by BF bag dust and BF gravitational dust. The reason for this is that the higher disordered crystalline structure leads to stronger gasification reactivity, and further results in stronger reduction reactivity. Based on the randomized nucleation model, the kinetic analysis shows that the activation energies for the reduction reaction of BF gravitational dust, BF bag dust, and raw coal after pickling are 300.14, 180.43, and 124.62 kJ mol{sup −1}, respectively.

36 MATERIALS SCIENCE↗