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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Effects of anomalous transport on the potentials of discrete auroral arcs

The evolution of U-shaped double layers in discrete auroral arcs occurs much faster than the global current in the arc flux tube can be redistributed. For asymptotic stability of the arc on MHD time scales, this implies that local transport mechanisms are required to charge the nearly field-aligned flanks of the equipotential structure over an extended region along the magnetic field. The diversion of the uniform upstream current provides a constraint which limits the double-layer potential.

Smith, R. A.↗
DOE OSTI2013

Single-Molecule Fluorescence Imaging of DNA at a Potential-Controlled Interface

Many interfacial chemical phenomena are governed in part by electrostatic interactions between polyelectrolytes and charged surfaces; these phenomena can influence the performance of biosensors, adsorption of natural polyelectrolytes (humic substances) on soils, and production of polyelectrolyte multilayer films. In order to understand electrostatic interactions that govern these phenomena, we have investigated the behavior of a model polyelectrolyte, 15 kbp fluorescently labeled plasmid DNA, near a polarized indium tin oxide (ITO) electrode surface. The interfacial population of DNA was monitored in situ by imaging individual molecules through the transparent electrode using total-internal-reflection fluorescence microscopy. At applied potentials of +0.8 V versus Ag/AgCl, the DNA interfacial population near the ITO surface can be increased by 2 orders of magnitude relative to bulk solution. The DNA molecules attracted to the interface do not adsorb to ITO, but rather they remain mobile with a diffusion coefficient comparable to free solution. Ionic strength strongly influences the sensitivity of the interfacial population to applied potential, where the increase in the interfacial population over a +300 mV change in potential varies from 20% in 30 mM ionic strength to over 25-fold in 300 μM electrolyte. The DNA accumulation with applied potential was interpreted using a simple Boltzmann model to predict average ion concentrations in the electrical double layer and the fraction of interfacial detection volume that is influenced by applied potential. A Gouy–Chapman model was also applied to the data to account for the dependence of the ion population on distance from the electrode surface, which indicates that the net charge on DNA responsible for interactions with the polarized surface is low, on the order of one excess electron. Furthermore, the results are consistent with a small fraction of the DNA plasmid being resident in the double-layer and with counterions screening much of the DNA excess charge.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Oxygen- and Nitrogen-Enriched 3D Porous Carbon for Supercapacitors of High Volumetric Capacity

Efficient utilization and broader commercialization of alternative energies (e.g., solar, wind, and geothermal) hinges on the performance and cost of energy storage and conversion systems. For now and in the foreseeable future, the combination of rechargeable batteries and electrochemical capacitors remains the most promising option for many energy storage applications. Porous carbonaceous materials have been widely used as an electrode for batteries and supercapacitors. To date, however, the highest specific capacitance of an electrochemical double layer capacitor is only ~200 F/g, although a wide variety of synthetic approaches have been explored in creating optimized porous structures. Here, we report our findings in the synthesis of porous carbon through a simple, one-step process: direct carbonization of kelp in an NH 3 atmosphere at 700 °C. The resulting oxygen- and nitrogen-enriched carbon has a three-dimensional structure with specific surface area greater than 1000 m 2 /g. When evaluated as an electrode for electrochemical double layer capacitors, the porous carbon structure demonstrated excellent volumetric capacitance (>360 F/cm 3 ) with excellent cycling stability. In conclusion, this simple approach to low-cost carbonaceous materials with unique architecture and functionality could be a promising alternative to fabrication of porous carbon structures for many practical applications, including batteries and fuel cells.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Energy dependent pitch angle distributions of auroral primary electrons

Double-layer/parallel-electric field accelerations and the subsequent electron-beam plasma interactions involving Cerenkov and anomalous cyclotron resonances are considered. It is found that these phenomena yield pitch angle distributions as noted from rocket and satellite studies. Although the electron acceleration by weak parallel electric fields forming a runaway electron tail is limited to a critical parallel energy determined by the anomalous cyclotron resonance, such a limitation does not occur with acceleration by a localized parallel electric field such as that in a double layer.

Singh, N.↗
DOE OSTI2017

Surface transport processes in charged porous media

Surface transport processes are important in chemistry, colloidal sciences, engineering, biology, and geophysics. Natural or externally produced charges on surfaces create electrical double layers (EDLs) at the solid-liquid interface. The existence of the EDLs produces several complex processes including bulk and surface transport of ions. In this work, a model is presented to simulate bulk and transport processes in homogeneous porous media comprising big pores. It is based on a theory for capacitive charging by ideally polarizable porous electrodes without Faradaic reactions or specific adsorption of ions. A volume averaging technique is used to derive the averaged transport equations in the limit of thin electrical double layers. Description of the EDL between the electrolyte solution and the charged wall is accomplished using the Gouy-Chapman-Stern (GCS) model. The surface transport terms enter into the average equations due to the use of boundary conditions for diffuse interfaces. Two extra surface transports terms appear in the closed average equations. One is a surface diffusion term equivalent to the transport process in non-charged porous media. The second surface transport term is a migration term unique to charged porous media. The effective bulk and transport parameters for isotropic porous media are calculated solving the corresponding closure problems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

A new oxytelluride: Perovskite and CsCl intergrowth in Ba{sub 3}Yb{sub 2}O{sub 5}Te

The new oxytelluride Ba{sub 3}Yb{sub 2}O{sub 5}Te was obtained from an alkaline earth flux. Ba{sub 3}Yb{sub 2}O{sub 5}Te crystallizes in the tetragonal space group P4/mmm (#123), with a=4.3615(3) Å and c=11.7596(11) Å, Z=1. The structure combines two distinct building blocks, a Ba{sub 2}Yb{sub 2}O{sub 5} perovskite-like double layer with square bipyramidal coordination of the ytterbium ions, and a CsCl-type BaTe layer. Short range magnetic order is apparent at below 5 K, with the magnetic behavior above this temperature dominated by crystal field effects. The structure may be considered as an analog to the Ruddlesden–Popper phases, where the NaCl-type layer has been replaced by the CsCl-type layer. The two-dimensional magnetic behavior is expected based on the highly anisotropic nature of the structure. - Graphical abstract: Optical images of Ba{sub 3}Yb{sub 2}O{sub 5}Te in transmission (left) and reflected (right) light, with atomic unit cell overlay. - Highlights: • Single crystal synthesis and characterization of a new phase, Ba{sub 3}Yb{sub 2}O{sub 5}Te. • The structure features the BaTe high pressure polymorph intergrowth. • Magnetic susceptibility measurements show short range 2 dimensional ordering. • Heat capacity measurements show a feature at the magnetic ordering temperature. • Optical reflectivity measurements show a {sup 2}F{sub 7/2}→{sup 2}F{sub 5/2} absorption at 976 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

A coupled mechanical and chemical damage model for concrete affected by alkali–silica reaction

To model the complex degradation phenomena occurring in concrete affected by alkali–silica reaction (ASR), we formulate a poro-mechanical model with two isotropic internal variables: the chemical and the mechanical damage. The chemical damage, related to the evolution of the reaction, is caused by the pressure generated by the expanding ASR gel on the solid concrete skeleton. The mechanical damage describes the strength and stiffness degradation induced by the external loads. As suggested by experimental results, degradation due to ASR is considered to be localized around reactive sites. The effect of the degree of saturation and of the temperature on the reaction development is also modeled. The chemical damage evolution is calibrated using the value of the gel pressure estimated by applying the electrical diffuse double-layer theory to experimental values of the surface charge density in ASR gel specimens reported in the literature. The chemo-damage model is first validated by simulating expansion tests on reactive specimens and beams; the coupled chemo-mechanical damage model is then employed to simulate compression and flexure tests results also taken from the literature. -- Highlights: •Concrete degradation due to ASR in variable environmental conditions is modeled. •Two isotropic internal variables – chemical and mechanical damage – are introduced. •The value of the swelling pressure is estimated by the diffuse double layer theory. •A simplified scheme is proposed to relate macro- and microscopic properties. •The chemo-mechanical damage model is validated by simulating tests in literature.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Selectively catalytic micro- and nanocrystals of metal–organic framework [Co(4-bpdh)(HIA)]{sub ∝}

Metal–organic framework micro-crystals [Co(4-bpdh)(HIA)]{sub ∝} (1Co), crystallized in the monoclinic system (space group P12/n1, a=10.0009(16) Å, b=15.472(3) Å, c=18.563(3) Å, β=91.81(0)°, and Z=4), were controllably synthesized through the adjustment of the solvent system. The Co{sup 2+} ion center located in a six-coordinated environment combined with 5-hydroxyisophthalic acid (HIA) to produce ladder-like structures, which again linked with 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hxadiene (4-bpdh) to yield a double-layer network. Micro-crystals 1Co exhibited selectively oxidation-catalytic properties for the degradation of methyl orange (conversion 90%) owing to ligand to metal charge transfer. Our work determined that the synthesized catalyst is not only highly selective for degradation of organic dyes, but also very efficient. - Graphical abstract: Metal–organic framework micro-crystals [Co(4-bpdh)(HIA)]{sub ∝} (1Co) were controllably synthesized through the adjustment of the solvent system. The Co{sup 2+} ion center located in a six-coordinated environment combined with the ligands to yield a double-layer network. Micro-crystals 1Co exhibited selectively catalytic properties for the degradation of methyl orange (conversion 90%) owing to ligand to metal charge transfer. - Highlights: • Synthesis and structure of metal–organic framework [Co(4-bpdh)(HIA)]{sub ∝}. • Selectively catalytic micro- and nanocrystals. • The degradation and conversion of methyl orange.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Capacitance enhancement via electrode patterning

The necessity of increasing the energy density in electric double layer capacitors to meet current demand is fueling fundamental and applied research alike. We report here molecular dynamics simulation results for aqueous electrolytes near model electrodes. Particular focus is on the effect of electrode patterning on the structure of interfacial electrolytes, and on the potential drop between the solid electrodes and the bulk electrolytes. The latter is estimated by numerically integrating the Poisson equation using the charge densities due to water and ions accumulated near the interface as input. We considered uniform and patterned electrodes, both positively and negatively charged. The uniformly charged electrodes are modeled as graphite. The patterned ones are obtained by removing carbon atoms from the top-most graphene layer, yielding nanoscopic squares and stripes patterns. For simplicity, the patterned electrodes are effectively simulated as insulators (the charge remains localized on the top-most layer of carbon atoms). Our simulations show that the patterns alter the structure of water and the accumulation of ions at the liquid-solid interfaces. Using aqueous NaCl solutions, we found that while the capacitance calculated for three positively charged electrodes did not change much, that calculated for the negatively charged electrodes significantly increased upon patterning. We find that both water structure and orientation, as well as ion accumulation affect the capacitance. As electrode patterning affects differently water structure and ion accumulation, it might be possible to observe ion-specific effects. These results could be useful for advancing our understanding of electric double layer capacitors, capacitive desalination processes, as well as of fundamental interfacial electrolytes properties.

36 MATERIALS SCIENCE↗
NASA NTRS1994

UV testing of INTELSAT-7, 7A, and 8 solar cells

A 4000 hour experiment, conducted in late 1992 through mid 1993, confirmed earlier results on the ultraviolet damage effects in covered solar cells of various types being used, or proposed for use, in INTELSAT programs. Two different UV test systems were used to identify systematic errors and to study the effects of UV source-bulb age on degradation rate. After correction for contamination and UV source-bulb aging, the extrapolated degradation rates for irradiated and unirradiated INTELSAT-5, -6 single AR(SAR) coated cells and INTELSAT-7, -7A, -8 double layer AR(DAR) coated cells in both the 1993 tests confirm the following hypotheses resulting from the 1992 experiment. (a) Irradiated cells display significantly more UV degradation than do the unirradiated cells for tests exceeding 2000 hours. The new data indicates that degradation effects from electron irradiation are proportional to t(exp 2) (the square of the UV hours), at least for times less than or equal to 3000 hours. (b) This difference does not depend upon entire reflective coating, cell resistivity, or manufacturer within the sensitivity and reproducibility of the experiment. (c) There is a clear difference in degradation rate between single AR coated cells (TiO(x)) and double layer AR coated cells (SiO(x) and Al2O3?). At 100,000 hours (11.4 years) the DAR coated cells display more degradation than do the SAR coated cells, even though at 1,000 hours the DAR cells display less degradation. (d) UV degradation rates, to modern covered silicon solar cells, at the beginning of bulb life drop from approximately 2 times the average rate to near zero after 2000 hours (average end-of-life for the xenon short-arc lamps used in the tests). The effects of 1 MeV electron irradiation (10(exp 15) e(-)/sq cm) prior to UV exposure are clearly indicated in the plot of percent change in cell open circuit voltage (Voc) versus percent change in short circuit current (Isc) during the UV test and post-test cleanup of the cells. Clearly, extended UV testing produces a permanent photo-induced redegradation of previously irradiated cells. However, this photo-induced redegradation may be caused by the long-wavelength light, not the UV light.

Meulenberg, A.↗
DOE OSTI2012

Effect of target composition on proton acceleration in ultraintense laser-thin foil interaction

The interactions of ultraintense circularly polarized laser pulses with a mixed solid target and a double-layer target are studied by two-dimensional particle-in-cell simulations. Different carbon and proton compositions in the targets are used in the simulations. It is shown that the proton acceleration mechanisms in both targets are very sensitive to the ion density ratios between protons and carbon ions. For a mixed solid target, a relatively low proton density gives rise to monoenergetic peaks in the proton energy spectrum while a high proton density leads to a large cut-off energy and wide energy spread. With the increase of the ratio, the so-called directed-Coulomb-explosion becomes dominated over the radiation pressure. Surprisingly, for a double-layer target with a front proton layer and an ultrathin rear carbon layer, a highly monoenergetic proton beam with a peak energy of 1.7 GeV/u, an energy spread of {approx}4%, and a divergency angle of 2 Degree-Sign can be obtained, which might have diverse applications in medical therepy and proton imaging in future.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Toward Engineering of Solution Microenvironments for the CO 2 Reduction Reaction: Unraveling pH and Voltage Effects from a Combined Density-Functional–Continuum Theory

Engineering the electrolyte microenvironment represents an attractive route to tuning the selectivity of electrocatalytic reactions beyond catalyst composition and morphology. However, harnessing the full potential of this approach requires understanding the interplay between voltage, electrolyte composition, and adsorbate binding within the electrical double layer, which is absent from the usual theoretical approaches. In this study, we apply a recently developed density functional theory (DFT)–continuum approach based on the effective screening medium method and reference interaction site model (ESM–RISM) to explore electrolyte effects with an enhanced description of the electrochemical interface. Furthermore, applying this method to the binding of CO adsorbates in potassium-containing electrolytes on copper, a problem of direct relevance to CO 2 electroreduction to value-added products, we show that the interdependence of voltage and pH leads to an unexpected change in adsorption site preference on Cu(001) terraces. Our findings highlight the often-overlooked importance of the electrical double-layer structure for predicting catalyst operation.

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

Single-step hydrothermal synthesis of wrinkled graphene wrapped TiO2 nanotubes for photocatalytic hydrogen production and supercapacitor applications

Highlights: • Wrinkle rGO wrapped TiO{sub 2} nanotubes were prepared by alkanine hydrothermal method. • Improved visible absorption and reduced recombination was witnessed in rGO-TiO{sub 2}. • H{sub 2} production of 24,880 μmole/g/h was achieved by rGO-TiO{sub 2}, 12.9 folds to P25 TiO{sub 2}. • Double layer and pseudo capacitance of rGO-TiO{sub 2} showed specific capacitance 160 F/g. - Abstract: Herein, we discuss the synthesis of reduced graphene oxide and TiO{sub 2} (rGO-TiO{sub 2}) nanocomposites with varying ratios of rGO to TiO{sub 2} by hydrothermal method. Photocatalytic ability of the nanocomposites was assessed for H{sub 2} production under natural sunlight. At 5 wt% GO loading, the rGO-TiO{sub 2} exhibited 24,880 μmol/g/h H{sub 2}, 12.9 times to commercial P25-TiO{sub 2} (1920 μmol/g/h). The symmetric supercapacitor device fabricated using rGO-TiO{sub 2} demonstrated 160 F/g specific capacitance with 99% retention. The efficient charge carrier separation and transportation between TiO{sub 2} nanotubes and rGO resulted high photocatalytic activity. The synergistic double layer pseudo capacitor behavior of rGO-TiO{sub 2} is the reason for improved specific capacitance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Intercalation studies of zinc hydroxide chloride: Ammonia and amino acids

Zinc hydroxide chloride (ZHC) is a layered hydroxide salt with formula Zn{sub 5}(OH){sub 8}Cl{sub 2}{center_dot}2H{sub 2}O. It was tested as intercalation matrix for the first time and results were compared with intercalation products of the well-known zinc hydroxide nitrate and a Zn/Al layered double hydroxide. Ammonia was intercalated into ZHC, while no significant intercalation occurred in ZHN. Aspartic acid intercalation was only achieved by co-precipitation at pH=10 with ZHC and pH=8 with zinc hydroxide nitrate. Higher pH resistance in ZHC favored total deprotonation of both carboxylic groups of the Asp molecule. ZHC conferred more thermal protection against Asp combustion presenting exothermic peaks even at 452 Degree-Sign C while the exothermic event in ZHN was 366 Degree-Sign C and in the LDH at 276 Degree-Sign C. - Graphical abstract: The zinc hydroxide chloride (ZHC) with formula Zn{sub 5}(OH){sub 8}Cl{sub 2}{center_dot}2H{sub 2}O was tested as intercalation matrix. In comparison with the well-known zinc hydroxide nitrate (ZHN) and layered double hydroxides (LDH), ZHC was the best matrix for thermal protection of Asp combustion, presenting exothermic peaks even at 452 Degree-Sign C, while the highest exothermic event in ZHN was at 366 Degree-Sign C, and in the LDH it was at 276 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Zinc hydroxide chloride (ZHC) was tested as intercalation matrix for the first time. Black-Right-Pointing-Pointer ZHC has higher chemical and thermal stability than zinc hydroxide nitrate and LDH. Black-Right-Pointing-Pointer NH{sub 3} molecules can be intercalated into ZHC. Black-Right-Pointing-Pointer The amino group of amino acids limits the intercalation by ion-exchange.

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

All Roads Lead to TiO 2 : TiO 2 -Rich Surfaces of Barium and Strontium Titanate Prepared by Hydrothermal Synthesis

Through high-resolution electron microscopy, the surface structure of barium titanate and strontium titanate nanoparticles are found to be terminated by a TiO 2 double layer. These results confirm prior observations of TiO 2 -rich surface reconstructions on strontium titanate nanoparticles made hydrothermally at high pH and single crystals prepared with wet chemical etching. Of all the reconstructions observed on single crystals for these two materials, we report for first time the √13 × √13R33.7° structure on the {001} facets of hydrothermally prepared barium titanate and strontium titanate nanocrystals. The aqueous environment common to the two preparation methods preferentially leaves strontium and barium depleted from the A-sites near the surface and leads to TiO 2 -terminated surfaces for both materials. Analysis indicates that the observed structures are the thermodynamic lowest energy structures in aqueous conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Correlated interlayer exciton insulator in heterostructures of monolayer WSe 2 and moiré WS 2 /WSe 2

Moiré superlattices in van der Waals heterostructures have emerged as a powerful tool for engineering quantum phenomena. Here, in this work, we report the observation of a correlated interlayer exciton insulator in a double-layer heterostructure composed of a WSe 2 monolayer and a WS 2 /WSe 2 moiré bilayer that are separated by ultrathin hexagonal boron nitride. The moiré WS 2 /WSe 2 bilayer features a Mott insulator state when the density of holes is one per moiré lattice site. When electrons are added to the Mott insulator in the WS 2 /WSe 2 moiré bilayer and an equal number of holes are injected into the WSe 2 monolayer, a new interlayer exciton insulator emerges with the holes in the WSe 2 monolayer and the electrons in the doped Mott insulator bound together through interlayer Coulomb interactions. The interlayer exciton insulator is stable up to a critical hole density in the WSe 2 monolayer, beyond which the interlayer exciton dissociates. Our study highlights the opportunities for realizing quantum phases in double-layer moiré systems due to the interplay between the moiré flat band and strong interlayer electron interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Molecular-Scale Structure of Electrode–Electrolyte Interfaces: The Case of Platinum in Aqueous Sulfuric Acid

Knowledge of the molecular composition and electronic structure of electrified solid-liquid interfaces is key to understanding elemental processes in heterogeneous reactions. Using X-ray absorption spectroscopy in the interface-sensitive electron yield mode (EY-XAS), first-principles electronic structure calculations, and multiscale simulations, we determined the chemical composition of the interfacial region of a polycrystalline platinum electrode in contact with aqueous sulfuric acid solution at potentials between the hydrogen and oxygen evolution reactions. We found that between 0.7 and 1.3 V vs Ag/AgCl the electrical double layer (EDL) region comprises adsorbed sulfate ions with hydrated hydronium ions in the next layer. No evidence was found for bisulfate or Pt-O/Pt-OH species, which have very distinctive spectral signatures. In addition to resolving the long-standing issue of the EDL structure, our work establishes interface- and element-sensitive EY-XAS as a powerful spectroscopic tool for studying condensed phase, buried solid-liquid interfaces relevant to various electrochemical processes and devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗