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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Electrochemical Structure of the Plasma–Liquid Interface

Nonthermal atmospheric pressure plasma in contact with a liquid yields a variety of energetic photons, ions, and electrons, which can be transported into the plasma–liquid interface (PLI). Similar to the electrochemical interface formed between a solid electrode and electrolyte in conventional electrochemical systems, the charge-transfer process across the PLI is able to promote reduction–oxidation (redox) reactions. However, in the case of free plasma jets in contact with liquids, the absence of solid electrodes obscures the spatial locations of the electrochemical half-reactions. Herein, we present a spatial electrochemical measurement technique used to characterize an aqueous solution in contact with an atmospheric pressure plasma jet. The technique is based on measuring the potential difference between two identical Ag/AgCl electrochemical electrodes positioned at different locations within the solution. More specifically, electrochemical maps were made by measuring the potential of one electrochemical electrode positioned at different locations near the PLI with respect to the other electrochemical electrode positioned far away from the PLI in the bulk solution. Regions in the map with negative and positive potential differences between these electrochemical electrodes were used to identify the electrodeless cathode and anode, respectively. Here, visualization of the spatial distribution of molecular colorimetric redox indicators by multispectral imaging revealed that reduction was occurring near the plasma jet centerline while oxidation was occurring further away in solution, which constitutes an independent confirmation of the electrochemical maps.

Absorption↗
DOE OSTI2021

Energetics of Ag Adsorption on and Adhesion to Rutile TiO 2 (100) Studied by Microcalorimetry

The adsorption and adhesion energies of vapor-deposited Ag on rutile TiO 2 (100) films have been measured using single crystal adsorption calorimetry (SCAC) and He + low energy ion scattering spectroscopy (LEIS). Ag grows as three-dimensional (3D) nanoparticles at 300 and 100 K. The saturation particle density is 8 × 10 16 particles/m 2 at 300 K and 2.5 × 10 17 particles/m 2 at 100 K. The differential heat of adsorption starts low, increases with Ag coverage, and finally approaches the sublimation enthalpy of Ag at both 300 and 100 K. At 300 K, the differential heat of adsorption starts from 208 kJ/mol and rises rapidly to 265 kJ/mol by 1 ML. At 100 K, Ag grows nanoparticles with smaller particle size on the terraces, while at 300 K, the Ag nanoparticles have bigger particle size and grow on step edges with stronger binding strength to the nanoparticles. Thus, the heat of Ag adsorption at 100 K starts at 141 kJ/mol (near the monomer size limit on terrace sites) and remains lower than that at 300 K until 1.5 ML. Here, the adhesion energy of Ag(solid) to rutile TiO 2 (100) is found to be large (~2.44 J/m 2 ), supporting a trend of decreasing adhesion energy with the enthalpy of oxide reduction.

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

High Performance Circuit Pastes for Solid Oxide Fuel Cell Applications: Final Technical Report

Using a combination of in-plane electrical conductivity measurements, electrical contact resistance measurements, tensile fracture tests, double shear lap fracture tests, rapid thermal cycling adhesion tests, in situ wetting angle measurements, 3D X-ray tomography, reduction-oxidation (RedOx) cycling, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDAX), Density Functional Theory (DFT) modeling, Molecular Dynamics (MD) modeling, and Phase Field modeling, this project determined that a new brazing technique developed by the PIs (specifically the use of nickel particles to direct the wetting and spreading of molten silver) could be used to produce well-adhered, >97% dense, electrically-conductive circuits, current collectors, and/or electrical contacts on a variety of ceramic and ceramic-coated substrates (specifically lanthanum strontium manganite, yttria stabilized zirconia, sapphire, Cr2O3-passivated stainless steel, and Al2O3-passivated stainless steel). Compared to other silver-based alternatives, Ag:Ni led to less manufacturing defects and was more tolerant of the extreme environments (isothermal high-temperature aging) and occasional abuse (rapid thermal cycling and RedOx cycling) encountered during Solid Oxide Fuel Cell and/or Solid Oxide Electrolysis Cell operation. Further, in some situations (such as when to produce Ag:Ni electrical contacts to Al2O3-protected stainless steel) the Ni particles also improved operation by acting as chemical getters that removed electrically-insulating, surface-segregating substrate impurities (i.e. by lowering the contact resistance with the underlying substrate).

36 MATERIALS SCIENCE↗
DOE OSTI2023

Platinum Surface Oxide and Oxygen Reduction Reaction Kinetics during Transient Fuel Cell Operation

Pt surface oxide coverage (POC) and Oxygen Reduction Reaction (ORR) were measured under a range of operating conditions in a Proton Exchange Membrane Fuel Cell (PEMFC). Sensitivity analysis suggests that adsorption of sulfonate groups of the ionomer on the Pt surface plays an important role in POC and ORR kinetics. Although both Pt oxide growth and ORR activity decay follow a logarithm of time behavior, it is found that ORR kinetics are affected by at least two different types of Pt oxide. A semi-empirical ORR kinetic model is proposed taking into account the effect of ionomer and Pt oxide types. The model is capable of providing a quantitative prediction of POC and ORR activity over a range of potential, temperature, relative humidity, and time that is relevant to normal PEMFC operation.

Electrochemistry↗
DOE OSTI2023

Accuracy of DFT computed oxygen-vacancy formation energies and high-throughput search of solar thermochemical water-splitting compounds

The enthalpy change involved in metal oxide reduction is a key quantity in various processes related to energy conversion and storage, and is of particular interest for computational prediction. Often this prediction involves the simulation of a high temperature reduction process with a 0K methodology like density functional theory (DFT), and it is not infrequent for the high temperature and 0K stable crystal structures to differ. This introduces a conundrum with regards to the choice of crystal structure to utilize in the computation, with approaches in the literature varying and experimental validation remaining scarce. In this work we address both the crystal structure conundrum and the experimental validation, and then apply the insights we gain to guide a high-throughput search for new materials for solar thermochemical water-splitting applications. By computing the DFT+U oxygen vacancy formation energy (ΔE vf ) of a selection of ABO 3 compounds and comparing different crystal structures for each composition, we highlight the issues that arise when the structure utilized in the computation is dynamically unstable at 0K, namely the presence of an artificial lowering of ΔE vf , and the lack of convergence of ΔE vf with cell size. We solve these limitations by identifying and employing a suitable surrogate dynamically stable structure. We then validate the predictive power of our calculations against appositely generated experimental measurements of reduction enthalpy for a series of Hubbard U values, finding an accuracy ranging between 0.2-0.6 eV/O. In light of such conclusions, we revise and expand a previous a high-throughput DFT study on ABO 3 perovskite oxides. As a result, we provide a list of candidate STCH materials, highlight trends with redox-active cation and structural distortion, and identify Mn 4+ , Mn 3+ and Co 3+ as the most promising redox-active cations.

08 HYDROGEN↗
DOE OSTI2022

Copper Single Atom-Triggered Niobia–Ceria Catalyst for Efficient Low-Temperature Reduction of Nitrogen Oxides

To reduce nitrogen oxide (NO x ) emission from diesel engines in the cold-start process benefitting the atmospheric environment, catalysts with superior low-temperature NO x removal efficiency are highly demanded. Herein, we report an efficient Nb 2 O 5 /CuO/CeO 2 (NbCuCe) oxide catalyst for the selective catalytic reduction (SCR) of NO x , showing much higher DeNO x activity below 200 °C, superior sulfur resistance, faster response, and much less NH 3 slip than the state-of-the-art Cu-CHA zeolite catalyst. Additionally, atomically dispersed Cu species facilitate the strong interaction between Cu and the Nb/Ce base catalyst, which significantly improves the low-temperature redox properties at Cu–O–Ce sites and NH 3 adsorption/activation at Nb–O–Cu sites, thus contributing to the superior SCR performance of NbCuCe at low temperatures. The developed NbCuCe catalyst is highly promising for efficient DeNO x from cold-start diesel engines and can be coupled with Cu-CHA to achieve a broad operation temperature window.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Compartment-specific energy requirements of photosynthetic carbon metabolism in Camelina sativa leaves

Abstract Main conclusion The oxidative pentose phosphate pathway provides cytosolic NADPH yet reduces carbon and energy use efficiency. Repressing this pathway and introducing cytosolic NADPH-dependent malate dehydrogenase may increase crop yields by ≈5%. Abstract Detailed knowledge about plant energy metabolism may aid crop improvements. Using published estimates of flux through central carbon metabolism, we phenotype energy metabolism in illuminated Camelina sativa leaves (grown at 22 °C, 500 µmol photons m −2 s −1 ) and report several findings. First, the oxidative pentose phosphate pathway (OPPP) transfers 3.3% of the NADPH consumed in the Calvin–Benson cycle to the cytosol. NADPH supply proceeds at about 10% of the rate of net carbon assimilation. However, concomitantly respired CO 2 accounts for 4.8% of total rubisco activity. Hence, 4.8% of the flux through the Calvin–Benson cycle and photorespiration is spent on supplying cytosolic NADPH, a significant investment. Associated energy requirements exceed the energy output of the OPPP. Thus, autotrophic carbon metabolism is not simply optimised for flux into carbon sinks but sacrifices carbon and energy use efficiency to support cytosolic energy metabolism. To reduce these costs, we suggest bioengineering plants with a repressed cytosolic OPPP, and an inserted cytosolic NADPH-dependent malate dehydrogenase tuned to compensate for the loss in OPPP activity (if required). Second, sucrose cycling is a minor investment in overall leaf energy metabolism but a significant investment in cytosolic energy metabolism. Third, leaf energy balancing strictly requires oxidative phosphorylation, cofactor export from chloroplasts, and peroxisomal NADH import. Fourth, mitochondria are energetically self-sufficient. Fifth, carbon metabolism has an ATP/NADPH demand ratio of 1.52 which is met if ≤ 21.7% of whole electron flux is cyclic. Sixth, electron transport has a photon use efficiency of ≥ 62%. Last, we discuss interactions between the OPPP and the cytosolic oxidation–reduction cycle in supplying leaf cytosolic NADPH.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Dynamic Tracking of NiFe Smart Catalysts using In Situ X-Ray Absorption Spectroscopy for the Dry Methane Reforming Reaction

The exsolution of nanoparticles from perovskite precursors has been explored as a route to synthesize catalysts with sinter or coke resistance. The characteristics of these exsolved nanoparticles are highly dynamic depending on the redox nature of the environment to which they are subjected. To develop their properties for thermo- and electrocatalytic applications, it is necessary to track the states and behavior of exsolved catalysts with in situ and ex situ characterization. In this study, we conduct in situ X-ray absorption spectroscopy (XAS) along with ex situ scanning transmission electron microscopy high-angle annular dark-field (STEM-HAADF) and energy-dispersive X-ray spectroscopy analysis of the parent perovskite oxide precursor, LaFe 0.8 Ni 0.2 O 3 , as its structure forms bimetallic NiFe nanoparticles and evolves in oxidative, reductive, and dry methane reforming environments. We develop a theory that NiFe exsolution is a function of the reduction potential where LaFe 0.8 Ni 0.2 O 3 transforms to NiFe alloy supported on LaO x -LaFeO x . The Ni starts to exsolve at 268 °C, while most Fe exsolves at 700 °C. During dry methane reforming conditions, most of the Fe is oxidized by CO 2 during the reaction and re-enters the perovskite as LaFeO 3 , while Ni remains on the surface as nanoparticles in the metallic state. During the oxidative regeneration phase, most of the Fe re-enters the bulk perovskite phase, while Ni is partially regenerated with a small percentage oxidized to large NiO nanoparticles. Finally, this study sheds light on the exsolution and regeneration of bimetallic alloy nanoparticles and the influence of the reaction conditions on their catalyst performance.

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

Time dependent zero valent iron oxidation and the reductive removal of pertechnetate at variable pH

Elemental iron Fe 0 is a promising reductant for removal of radioactive technetium-99 (Tc) from complex aqueous waste streams that contain sulfate, halides, and other inorganic anions generated during processing of legacy radioactive waste. The impact of sulfate on the kinetics of oxidation and reduction capacity of Fe 0 in the presence of Tc has not been examined. We investigated the oxidative transformation of Fe 0 and reductive removal of TcO 4 - in 0.1 M Na 2 SO 4 as a function of initial pH (i.e., pH i 4, 7, and 10) under aerobic conditions up to 30 days. Tc reduction was the fastest at pH i 7 and slowest at pHi 10 (Tc reduction rate pHi 7 > 4 > 10). Aqueous fraction of Tc was measured at 0.4% at pH i 7 within 6 h, whereas ≥ 97% of Tc was removed from solutions at pH i of 4 and 10 within 24 h. Solid phase characterization showed that magnetite was the only oxidized crystalline phase for the first 6 h regardless of initial pH. Lepidocrocite was the most abundant oxidized product for pH i 10 after 5 days, but was not observed at pH of 4 or 7.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Sequential oxidation-depolymerization strategies for lignin conversion to low molecular weight aromatic chemicals

Lignin is the largest source of bio-derived aromatic chemicals, and oxidative conversion of this polymeric material can generate valuable oxygenated aromatic compounds. Oxidative depolymerization of lignosulfonate feedstocks under alkaline conditions is used commercially for vanillin production. Recent studies have led to other oxidation methods that access different aromatic products from lignin in good yields. A particularly effective strategy that accesses some of the highest yields of aromatic monomers to date features a two-step process in which the oxidation of specific alcohol groups in lignin is followed by an oxidative, reductive, or redoxneutral step that cleaves the polymer into aromatic monomers and oligomers. Studies of model compounds have provided crucial mechanistic insights and contributed to the development of effective lignin depolymerization methods. Furthermore, this review provides a general overview of lignin depolymerization methods, followed by a survey of oxidation-depolymerization methods that access oxygenated aromatic monomers in good yields.

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

Cryptic cycling by electroactive bacterioplankton in Trout Bog Lake

The potential for extracellular electron transfer (EET) is a prevailing genomic feature of humic lake bacterioplankton. However, there has been little evidence for the substantial ecological contribution predicted by genetics. We hypothesized that anoxygenic phototrophic electrotrophs and accompanying heterotrophic electrogens cycle dissolved organic matter (DOM) between oxidized and reduced states. We predicted that such bacterioplankton would exhibit diel-scale oscillations due to the light dependency of photosynthesis. Using Trout Bog Lake in Wisconsin, USA, as our model ecosystem, we profiled the water column with depth-discrete metagenomic, physiochemical, and electrochemical analyses. We observed variation in oxidation reduction potential (ORP) in response to sunlight, initiating at depths populated by anoxygenic phototrophs with EET genes. We developed an automated buoy to measure electric current flow between many pairs of electrodes simultaneously, observing correlation in electron consumption to sunlight. Our results, combined with published metatranscriptomic analysis, indicate the occurrence of electron cycling between phototrophic oxidation (electrotrophic metabolism) by Chlorobium and anaerobic respiration (electrogenic metabolism) by Geothrix, involving DOM. We also repeatedly observed gradual seasonal increases in hypolimnion ORP throughout summer. These diel and seasonal patterns imply that electroactive DOM mediates the ecology of electroactive bacteria in lakes, controlling humic lake methane emissions.IMPORTANCEWe investigated the physical, chemical, and redox characteristics of a bog lake and electrodes hung therein to test the hypothesis that dissolved organic matter is being cycled between oxidized and reduced states by electroactive bacterioplankton powered by phototrophy. To do so, we performed field-based analyses on multiple timescales using both established and novel instrumentation. We paired these analyses with recently developed bioinformatics pipelines for metagenomics data to investigate genes that enable electroactive metabolism and accompanying metabolisms. Our results are consistent with our hypothesis and yet upend some of our other expectations. Our findings have implications for understanding greenhouse gas emissions from lakes, including electroactivity as an integral part of lake metabolism throughout more of the anoxic parts of lakes and for a longer portion of the summer than expected. Our results also give a sense of what electroactivity occurs at given depths and provide a strong basis for future studies.

carbon emissions↗
DOE OSTI2024

Air separation and N 2 purification with Ba 0.15 Sr 0.85 FeO 3-$δ$ via a two-step thermochemical process

Thermochemical air separation to produce high-purity N 2 was demonstrated in a vertical tube reactor via a two-step reduction–oxidation cycle with an A-site substituted perovskite Ba 0.15 Sr 0.85 FeO 3–δ (BSF1585). BSF1585 particles were synthesized and characterized in terms of their chemical, morphological, and thermophysical properties. A thermodynamic cycle model and sensitivity analysis using computational heat and mass transfer models of the reactor were used to select the system operating parameters for a concentrating solar thermal-driven process. Thermal reduction up to 800 °C in air and temperature-swing air separation from 800 °C to minimum temperatures between 400 and 600 °C were performed in the reactor containing a 35 g packed bed of BSF1585. The reactor was characterized for dispersion, and air separation was characterized via mass spectrometry. Gas measurements indicated that the reactor produced N 2 with O 2 impurity concentrations as low as 0.02 % for > 30 min of operation. Additionally, a parametric study of air flow rates suggested that differences in observed and thermodynamically predicted O 2 impurities were due to imperfect gas transport in the bed. Temperature swing reduction/oxidation cycling experiments between 800 and 400 °C in air were conducted with no statistically significant degradation in N 2 purity over 50 cycles.

14 SOLAR ENERGY↗
DOE OSTI2020

Stabilization of Uranium Metal by Chloride Conversion-Economical, Safe, Scalable [Factsheet]

Researchers at Los Alamos National Laboratory have developed SUCCESS, a process to convert uranium metal to uranium tetrachloride enabling production of these valuable compounds for actinide science, molten salt nuclear reactors, and energy research. Conventional methods are problematic due to the oxide reduction processes use rare reagents and generate significant amounts of waste and hydride conversion process using chlorine at high temperature is hazardous. This new method using inexpensive reagents chemically transform uranium metal into uranium halide compounds under mild conditions. The facile conversion to stable uranium tetrachloride could reduce the need to mine uranium for uses other than nuclear, by recycling the uranium without oxidation. The Laboratory is interested in supporting further scale-up efforts using a Cooperative Research and Development Agreement (CRADA) or by granting a license to a qualified entity

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Thermodynamic controls on the synthesis, structure and reactivity of materials for energy (Final Report)

The major objectives have been: a) to advance and use unique calorimetric capabilities to determine the energetics of oxide and other materials having possible energy applications, with an emphasis on new materials for batteries, fuel cells and solar energy conversion, b) to understand, in terms of both macroscopic energetics and microscopic structure and bonding, the interplay of defect chemistry, oxidation-reduction, and size effects at the bulk and nanoscale in determining materials properties. This project emphasizes mixed ionic-electronic conduction materials containing transition metals of variable valence, especially perovskites and lithium containing phases, with M = Mn, Fe, Co, Ni. The thermochemistry of new families of complex halide, chalcogenide, nitride and hybrid (organic-inorganic) perovskite materials were explored. The major and unique technique employed is high temperature oxide melt solution calorimetry, with careful attention given to materials synthesis and characterization. The thermochemical studies will be coupled with structural studies, especially to characterize order-disorder phenomena by in situ high temperature diffraction techniques.

14 SOLAR ENERGY↗
DOE OSTI2024

Electrocatalytic Effects of Au Nanoclusters in its Electrochemiluminescence Enhanced by Coreactant Tertiary Amines

Abstract Atomically precise metal nanoclusters are increasingly exploited in electrocatalysis such as water electrolysis and CO 2 reduction. The catalytic effects are generally evaluated by conventional electrochemical methods or end‐product analysis. Herein, near infrared electrochemiluminescence (ECL) of the nanoclusters is introduced as a new signaling mechanism to complement classical voltammetric analysis for elucidating essential electrocatalytic parameters. Coreactant ECL from an aqueous soluble Au 22 nanocluster (NCs) enhanced by a common pH buffer materials 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid (HEPES) and by a piperazine drug hydroxyzine (HDZ) is studied under oxidative reduction pathways. Foot of the wave analysis on voltametric features and the kinetics profiles in potential‐step experiments are studied in different nanocluster and coreactant concentrations. Benchmark parameters such as rate constants are determined under EC (Electron‐transfer‐Chemical‐reaction) mechanism as feasibility validations. Because the luminescence properties of AuNCs are sensitive to the surface ligands or adsorbents, ECL is proposed as a new signal readout for operando studies providing insights for governing reaction mechanism and kinetics during catalytic reactions. Retrospectively, mechanistic understanding of the complex multi‐step reactions during ECL generation can provide guidance for the evaluation and optimization of ECL property for better quantitative applications.

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

Fischer-Tropsch Synthesis: The Characterization and Testing of Pt-Co/SiO 2 Catalysts Prepared with Alternative Cobalt Precursors

Different low-cost cobalt precursors (acetate, chloride) and thermal treatments (air calcination/H 2 reduction versus direct H 2 -activation) were investigated to alter the interaction between cobalt and silica. H 2 -activated catalysts prepared from cobalt chloride had large Co 0 particles (XRD, chemisorption) formed by weak interactions between cobalt chloride and silica (temperature programmed reduction (TPR), TPR with mass spectrometry (TPR-MS), TPR with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge spectroscopy (XANES) techniques) and retained Cl-blocked active sites, resulting in poor activity. In contrast, unpromoted Co/SiO 2 catalysts derived from cobalt acetate had strong interactions between Co species and silica (TPR/TPR-MS, TPR-EXAFS/XANES); adding Pt increased the extent of the Co reduction. For these Pt-promoted catalysts, the reduction of uncalcined catalysts was faster, resulting in larger Co 0 clusters (19.5 nm) in comparison with the air-calcined/H 2 -activated catalyst (7.8 nm). Both catalysts had CO conversions 25% higher than that of the Pt-promoted catalyst prepared in the traditional manner (air calcination/H 2 reduction using cobalt nitrate) and three times higher than that of the traditional unpromoted Co/silica catalyst. The retention of residual cobalt carbide (observed in XANES) from cobalt acetate decomposition impacted performance, resulting in a higher C 1 –C 4 selectivity (32.2% for air-calcined and 38.7% for uncalcined) than that of traditional catalysts (17.5–18.6%). The residual carbide also lowered the α-value and olefin/paraffin ratio. Future work will focus on improving selectivity through oxidation–reduction cycles.

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

Electrochemical Investigation of Moisture Byproducts in Molten Calcium Chloride

Residual water in molten CaCl 2 reacts to form different byproducts, such as HCl, which can impact the corrosivity of the salt and efficiency of electrochemical operations, such as electrolytic oxide reduction and electrorefining. The ability to detect and quantify these byproducts electrochemically can provide feedback on the efficacy of vacuum drying and other purification methods, as well as the impact of these byproducts on process operations. An electrochemical signal’s association with the production of H 2 is verified and characterized using cyclic voltammetry (CV) and residual gas analysis. CV estimated a 2-electron exchange process associated with H 2 production. CV detected trace quantities of an oxidized species containing hydrogen in the salt on the order of 10 ppm. Different salt handling methods were compared for their impact on the hydrogen electrochemical signal. It was found that 30 min of exposure of CaCl 2 in a beaker to low-humidity air (<20%) had minimal impact on the H 2 production signal.

Electrochemistry↗