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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Controlled One‐pot Synthesis of Nickel Single Atoms Embedded in Carbon Nanotube and Graphene Supports with High Loading

Abstract Single‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C 3 N 4 , g‐C 3 N 4 −Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C 3 N 4 −Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C 3 N 4 ‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO 2 reduction reaction (CO 2 RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs.

Zhao, Shiyong↗
DOE OSTI2026

Ultranano Titania: Selectively Ridding Water of Persistent Organic Pollutants

Persistent organic pollutants, including the EPA's “dirty dozen”, are difficult to remove from water supplies due to their chemical stability. Here, we report a stable oxide photocatalyst, ultranano titania (d < 2 nm) doped with iron, Fe•TiUNP, that efficiently mineralizes multiple persistent pollutants including aromatic compounds plus common troublesome, difficult-to-oxidize intermediates such as formaldehyde and acetone, netting mineralization of persistent pollutants. Efficiency stems from a direct charge-transfer pathway. The key role of iron doping is to lower the reduction potential of the photogenerated electron so that it is insufficient to reduce water, thus eliminating competition from the hydrogen evolution reaction. The reduction potential of the localized electron is similarly insufficient to reduce quinone, enabling breaking aromaticity. Specific results for degrading acetone, phenol, benzoic acid, and 1,4-benzoquinone are reported.

alcohols↗
DOE OSTI2016

Supramolecular gel-assisted synthesis of double shelled Co@CoO@N-C/C nanoparticles with synergistic electrocatalytic activity for the oxygen reduction reaction

Investigating active, stable, and low-cost materials for the oxygen reduction reaction is one of the key challenges in fuel-cell research. In this work, we describe the formation of N-doped carbon shell coated Co@CoO nanoparticles supported on Vulcan XC-72 carbon materials (Co@CoO@N–C/C) based on a simple supramolecular gel-assisted method. The double-shelled Co@CoO@N–C/C core–shell nanoparticles exhibit superior electrocatalytic activities for the oxygen reduction reaction compared to N-doped carbon and cobalt oxides, demonstrating the synergistic effect of the hybrid nanomaterials. Notably, the Co@CoO@N–C/C nanoparticles give rise to a comparable four-electron selectivity, long-term stability, and high methanol tolerance; all show a multi-fold improvement over the commercial Pt/C catalyst. As a result, the progress is of great importance in exploring advanced non-precious metal-based electrocatalysts for fuel cell applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High capacity lithium ion batteries having oxides, peroxides, or superoxides as cathode active material

Described herein is an electrochemical device including a cathode containing an electroactive material including LO.sub.2 or L.sub.2O.sub.2, wherein each L is independently selected from Li, Na, K, Be, Mg, Ca, and Al; the electroactive material is carbon-coated, metal-coated, metal oxide-coated, nano-sized, or doped; and the electroactive material is substantially free of transition metal catalyst.

Lu, Jun↗
DOE OSTI2019

Electrochemistry of the Arrow Poison, Tubocurarine, Using Boron Doped Diamond Electrode: Experimental and Theoretical Approaches

In present work boron doped diamond (BDD) electrode was applied for studying electrochemical behavior, as well as for quantitative determination of natural alkaloid, tubocurarine (arrow poison/ TUB). Electrochemical behavior was investigated using several organic solvents and aqueous buffers, at different pHs, as supporting electrolytes. After selection of the most appropriate supporting electrolyte and investigation of its electrochemical behavior, analytical procedures for quantitative analysis of TUB were developed in an acetonitrile/methanol (80:20) mixture and in 1 mol L−1 nitric acid, which had linear quantification ranges from 4 × 10−6 to 1 × 10−4 mol L−1 (LOD = 3.07 × 10−6 mol L−1) and 4 × 10−6 to 9 × 10−5 mol L−1 (LOD = 2.45 × 10−6 mol L−1 and 5.28 × 10−7 mol L−1, depending on the selected peak), respectively. The oxidation mechanism of TUB was proposed from the theoretical aspect. Remarkable selectivity and good sensitivity were obtained after the TUB quantification method was optimized, allowing application of the developed method for TUB quantification in biological fluids, with excellent reproducibility, accuracy and precision.

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

Sol-gel preparation and characterization of Er3+ doped TiO2 luminescent nanoparticles

Highlights: • Sol-gel derived Er{sup 3+} doped TiO{sub 2} nanoparticles for potential use in solar cells and bio imaging. • Influence of Er{sup 3+} doping into TiO{sub 2} with various Er{sup 3+} concentration on structural, optical, and luminescence properties. • Down-and up-conversion luminescence behaviour of Er{sup 3+} doped titanium dioxide. - Abstract: The present paper reports on down-and up-conversion luminescence behaviour of sol-gel derived erbium doped titanium dioxide with anatase structure. Through combined structural, optical and electron microscope analysis, effective and influence of Er{sup 3+} doping into TiO{sub 2} lattice has been demonstrated using X-Ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and optical reflectance spectra. XRD results showed only anatase diffraction peaks of TiO{sub 2}, indicating the formation of a pure anatase phase even after Er{sup 3+} incorporation into TiO{sub 2} lattice. Selected Area Electron Diffraction (SAED) confirmed that the synthesized TiO{sub 2} nanoparticles are polycrystalline in nature which correlated well with XRD findings. Upon excitation at 320 nm, two down-conversion contributions at 378 nm and 435 nm attributed to indirect band gap and defect-related emissions, respectively were observed from both pure and Er{sup 3+} doped TiO{sub 2} nanoparticles. On the other hand, strong green up-conversion emission centred at 544 nm ascribed to {sup 4}S{sub 3/2 }→ {sup 4}I{sub 15/2} transition of Er{sup 3+} was observed under 980 nm laser excitation for all Er{sup 3+} doped TiO{sub 2} samples. This result analysis brings insight on understanding of structural, optical and luminescence properties of Er{sup 3+} doped TiO{sub 2} nanoparticles for use in solar cells and bio imaging devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Enhanced multi-carbon alcohol electroproduction from CO via modulated hydrogen adsorption

Multi-carbon alcohols such as ethanol are valued as fuels in view of their high energy density and ready transport. Unfortunately, the selectivity toward alcohols in CO 2 /CO electroreduction is diminished by ethylene production, especially when operating at high current densities (>100 mA cm –2 ). Here we report a metal doping approach to tune the adsorption of hydrogen at the copper surface and thereby promote alcohol production. Using density functional theory calculations, we screen a suite of transition metal dopants and find that incorporating Pd in Cu moderates hydrogen adsorption and assists the hydrogenation of C 2 intermediates, providing a means to favour alcohol production and suppress ethylene. We synthesize a Pd-doped Cu catalyst that achieves a Faradaic efficiency of 40% toward alcohols and a partial current density of 277 mA cm –2 from CO electroreduction. The activity exceeds that of prior reports by a factor of 2.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

A high energy density relaxor antiferroelectric pulsed capacitor dielectric

Pulsed capacitors require high energy density and low loss, properties that can be realized through selection of composition. Ceramic (Pb{sub 0.88}La{sub 0.08})(Zr{sub 0.91}Ti{sub 0.09})O{sub 3} was found to be an ideal candidate. La{sup 3+} doping and excess PbO were used to produce relaxor antiferroelectric behavior with slim and slanted hysteresis loops to reduce the dielectric hysteresis loss, to increase the dielectric strength, and to increase the discharge energy density. The discharge energy density of this composition was found to be 3.04 J/cm{sup 3} with applied electric field of 170 kV/cm, and the energy efficiency, defined as the ratio of the discharge energy density to the charging energy density, was 0.920. This high efficiency reduces the heat generated under cyclic loading and improves the reliability. The properties were observed to degrade some with temperature increase above 80 °C. Repeated electric field cycles up to 10 000 cycles were applied to the specimen with no observed performance degradation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2002

A Statistical Analysis of Laser Ablated Ba(Sub 0.50)Sr(Sub 0.50)TiO(Sub 3)/LaAlO(Sub 3) Films for Microwave Applications

The NASA Glenn Research Center is constructing a 616 element scanning phased array antenna using thin film Ba(sub x)Sr(sub 1-x)TiO(sub 3) based phase shifters. A critical milestone is the production of 616 identical phase shifters at 19 GHz with [asymptotically equal to]4 dB insertion loss and at least 337.5 deg phase shift with 3 percent bandwidth. It is well known that there is a direct relationship between dielectric tuning and loss due to the Kramers-Kronig relationship and that film crystallinity and strain, affected by the substrate template, play an important role. Ba(sub 0.50)Sr(sub 0.50)TiO (sub 3) films, nominally 400 nm thick, were deposited on 48 0.25 mm thick, 5 cm diameter LaAlO(sub 3) wafers. Although previous results suggested that Mn-doped films on MgO were intrinsically superior in terms of phase shift per unit loss, for this application phase shift per unit length was more important. The composition was selected as a compromise between tuning and loss for room temperature operation (e.g. crystallinity progressively degrades for Ba concentrations in excess of 30 percent). As a prelude to fabricating the array, it was necessary to process, screen, and inventory a large number of samples. Variable angle ellipsometry was used to characterize refractive index and film thickness across each wafer. Microstructural properties of the thin films were characterized using high resolution X-ray diffractometry. Finally, prototype phase shifters and resonators were patterned on each wafer and RE probed to measure tuning as a function of dc bias voltage as well as peak (0 field) permittivity and unloaded Q. The relationship among film quality and uniformity and performance is analyzed. This work presents the first statistically relevant study of film quality and microwave performance and represents a milestone towards commercialization of thin ferroelectric films for microwave applications.

Ferroelectric thin films↗
DOE OSTI2019

Passivating contacts for crystalline silicon solar cells

The global photovoltaic (PV) market is dominated by crystalline silicon (c-Si) based technologies with heavily doped, directly metallized contacts. Recombination of photo-generated electrons and holes at the contact regions is increasingly constraining the power conversion efficiencies of these devices as other performance-limiting energy losses are overcome. To move forward, c-Si PV technologies must implement alternative contacting approaches. Passivating contacts, which incorporate thin films within the contact structure that simultaneously supress recombination and promote charge-carrier selectivity, are a promising next step for the mainstream c-Si PV industry. Here, we review the fundamental physical processes governing contact formation in c-Si. In doing so we identify the role passivating contacts play in increasing c-Si solar cell efficiencies beyond the limitations imposed by heavy doping and direct metallization. Strategies towards the implementation of passivating contacts in industrial environments are discussed.

14 SOLAR ENERGY↗
DOE OSTI2014

Facile synthesis, structural characterization, and photoluminescence mechanism of Dy{sup 3+} doped YVO{sub 4} and Ca{sup 2+} co-doped YVO{sub 4}:Dy{sup 3+} nano-lattices

Light plays a vital role in the evolution of life. From sunlight to candle-light and then to other form of lighting devices, human beings are utilizing light since time immemorial. Lighting devices such as conventional incandescent lamp and fluorescent lamp have been replaced by Light Emitting Diodes (LEDs) for the later is cheap, durable, etc. Now-a-days, phosphor converted LEDs have been burning issues in the fabrication of lighting devices. Especially, lanthanide ion(s) doped phosphors are of great interest for the same. However, doped phosphors have a limitation of luminescence quenching, i.e., instead of increasing luminescence on increasing dopant concentration, the luminescence decreases. Therefore, it must be rectified by one or other means so as to get maximum desirable intensity for uses in display or lighting devices. In the present work, YVO{sub 4}:Dy{sup 3+} and YVO{sub 4}:Dy{sup 3+}/Ca{sup 2+} nano-lattices are synthesized by a facile technique. Structural characterizations such as x-ray diffraction, SEM, TEM, HRTEM, and Selected Area Electron Diffraction (SAED) of the samples are reported. Photoluminescence (PL) excitation and emission, enhanced mechanism, and lifetime are thoroughly discussed. PL intensity of the quenched YVO{sub 4}:Dy{sup 3+} is made increased up to 432.63% by Ca{sup 2+} co-doping. Role of the Ca{sup 2+} on the luminescence enhanced mechanism of YVO{sub 4}:Dy{sup 3+}/Ca{sup 2+} is elucidated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Modulation of a solid-state reversible fluorescent photoswitching based on a controllable photochromic pyrazolones

A novel solid-state reversible fluorescence photoswitching system (FPS) based on photochromism of photochromic pyrazolones has been developed by employing phosphor Sr{sub 2}P{sub 2}O{sub 7} co-doped with europium ion and chlorine ion (Sr{sub 2}P{sub 2}O{sub 7}–EC) and 1,3-diphenyl-4-(3-chlorobenzal)-5-hydroxypyrazole-4-phenylsemicarbazone (1a) as the fluorescence dye and the photochromic compound, respectively. With carefully selected components, the absorption band of the keto-form photochromic pyrazolones well overlaps with the emission peak of Sr{sub 2}P{sub 2}O{sub 7}–EC. The fluorescence emission intensity of Sr{sub 2}P{sub 2}O{sub 7}–EC is efficiently modulated by the photoisomerization of 1a with controlling the exposure time in the solid state. The fluorescence photoswitching system displayed high fluorescence quenching efficiency and remarkable fatigue resistance. It can be repeated 7 cycles without observable the changes of emission intensity. A fluorescence quenching efficiency can be achieved with a reversible colour change from white to yellow. - Graphical abstract: A novel fluorescence photoswitching system based on doping inorganic fluorescence dye into photochromic pyrazolones was constructed successfully. Its fluorescence emission could be efficiently modulated by the photoisomerization of pyrazolones. - Highlights: • A solid-state fluorescence photoswitching material was prepared. • Photoswitching is due to energy transfer between pyrazolone and fluorescence dye. • It exhibits excellent fluorescence contrast and fatigue resistance in the solid state.

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

A broadband-sensitive upconverter La(Ga{sub 0.5}Sc{sub 0.5})O{sub 3}:Er,Ni,Nb for crystalline silicon solar cells

We have developed an upconverter that significantly broadens the sensitive range, to overcome the shortcoming that conventional Er{sup 3+}-doped upconverters used for crystalline silicon solar cells can utilize only a small portion of the solar spectrum at around 1.55 μm. We have designed the combination of the sensitizers and host material to utilize photons not absorbed by silicon or Er{sup 3+} ions. Ni{sup 2+} ions have been selected as the sensitizers that absorb photons in the wavelength range between the silicon absorption edge (1.1 μm) and the Er{sup 3+} absorption band and transfer the energies to the Er{sup 3+} emitters, with La(Ga,Sc)O{sub 3} as the host material. The Ga to Sc ratio has been optimized to tune the location of the Ni{sup 2+} absorption band for sufficient energy transfer. Co-doping with Nb{sup 5+} ions is needed for charge balance to introduce divalent Ni{sup 2+} ions into the trivalent Ga{sup 3+} and Sc{sup 3+} sites. In addition to 1.45–1.58 μm photons directly absorbed by the Er{sup 3+} ions, we have demonstrated upconversion of 1.1–1.35 μm photons in the Ni{sup 2+} absorption band to 0.98 μm photons, using 10% Er, 0.5% Ni, and 0.5% Nb-doped La(Ga{sub 0.5}Sc{sub 0.5})O{sub 3}. The broadband-sensitive upconverter developed here can improve conversion efficiency of crystalline silicon solar cells more notably than conventional ones.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Intertwined charge, spin, and pairing orders in doped iron ladders

Motivated by recent experimental progress on iron-based ladder compounds, we study the doped two-orbital Hubbard model for the two-leg ladder BaFe2S3. The model is constructed by using ab initio hopping parameters and the ground state properties are investigated using the density matrix renormalization group method. We show that the (π,0) magnetic ordering at half filling, with ferromagnetic rungs and antiferromagnetic legs, becomes incommensurate upon hole doping. Moreover, depending on the strength of the Hubbard U coupling, other magnetic patterns, such as (0,π), are also stabilized. We found that the binding energy for two holes becomes negative for intermediate Hubbard interaction strength, indicating hole pairing. Due to the crystal-field split among orbitals, the holes primarily reside in one orbital, with the other one remaining half filled. This resembles orbital selective Mott states. The formation of tight hole pairs continues with increasing hole density, as long as the magnetic order remains antiferromagnetic in one direction. The study of pair-pair correlations indicates the dominance of the intraorbital spin-singlet channel, as opposed to other pairing channels. Although in a range of hole doping pairing correlations decay slowly, our results can also be interpreted as corresponding to a charge density wave made of pairs, a precursor of eventual superconductivity after interladder couplings are included. Such a scenario of intertwined orders has been extensively discussed before in the cuprates, and our results suggest a similar physics could exist in ladder iron-based superconductors. Finally, we also show that a robust Hund's coupling is needed for pairing to occur.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Low cost fabrication of highly sensitive ethanol sensor based on Pd-doped α-Fe2O3 porous nanotubes

Highlights: • Novel porous tubular nanostructures of α-Fe{sub 2}O{sub 3} are proposed. • The sensor based on 3.0 wt% Pd-doped α-Fe{sub 2}O{sub 3} porous nanotubes exhibited superior gas-sensing properties to ethanol. • The detection limit of the sensor for ethanol gas is as low as 0.1 ppm at 240 °C. • The sensor possesses an excellent reproducibility and good linearity (0.1–400 ppm) in ethanol detection. - Abstract: Pure and Pd-doped α-Fe{sub 2}O{sub 3} porous nanotubes (PNTs) are synthesized by a facile electrospinning approach. Different Pd dopant concentrations are introduced to investigate the dopant’s role in sensing performance. The structures and chemical compositions of the as-prepared products are examined using a series of characterization methods including XRD, EDS, SEM, TEM, XPS and BET. The gas-sensing properties of the sensor based on above PNTs are studied. And the results reveal that, compared with pure α-Fe{sub 2}O{sub 3}, the 3.0 wt% Pd-doped α-Fe{sub 2}O{sub 3} PNTs sensors exhibit superior performance in ethanol detection (at 240 °C). The highest sensitivity reaches 65.4 for 50 ppm ethanol and the detection limit is as low as 0.1 ppm. In addition, the sensors also show excellent selectivity, good long-term stability and as well as rapid response/recovery time (8 s/30 s, respectively) to ethanol. The improvement of sensing performance is mainly attributed to the dramatic sensitization of the additional Pd components.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Ni 3 Fe-N Doped Carbon Sheets as a Bifunctional Electrocatalyst for Air Cathodes

A promising bifunctional electrocatalyst is reported for air cathodes consisting of Ni 3 Fe nanoparticles embedded in porous nitrogen–doped carbon sheets (Ni 3 Fe/N–C sheets) by a facile and effective pyrolysis–based route with sodium chloride (NaCl) crystals as a template. Here, the Ni 3 Fe/N–C sheets show excellent catalytic activity, selectivity, and durability toward both the oxygen–reduction and oxygen–evolution reactions (ORR and OER). They are shown to provide a superior, low–cost cathode for a rechargeable Zn–air battery. At a discharge–charge current density of 10 mA cm –2 , the Ni 3 Fe/N–C sheets enable a Zn–air battery to cycle steadily up to 420 h with only a small increase in the round–trip overpotential, outperforming the more costly Pt/C + IrO 2 mixture catalyst (160 h). With the simplicity and scalability of the synthetic approach and its remarkable bifunctional electrocatalytic performance, the Ni 3 Fe/N–C sheets offer a promising rechargeable air cathode operating at room temperature in an alkaline electrolyte.

36 MATERIALS SCIENCE↗
DOE OSTI2024

2D Nitrogen‐Doped Graphene Materials for Noble Gas Separation

Abstract Noble gases, notably xenon, play a pivotal role in diverse high‐tech applications. However, manufacturing xenon is an inherently challenging task, due to its unique properties and trace abundance in the Earth's atmosphere. Consequently, there is a pressing need for the development of efficient methods for the separation of noble gases. Using mild fluorographene chemistry, nitrogen‐doped graphene (GNs) materials are synthesized with abundant aromatic regions and extensive nitrogen doping within the vacancies and holes of the aromatic lattice. Due to the organized interlayer “nanochannels”, nitrogen functional groups, and defects within the two‐dimensional (2D) structures, GNs exhibits effective selectivity for Xe over Kr at low pressure. This enhanced selectivity is attributed to the stronger binding affinity of Xe to GN compared to Kr. The adsorption is governed by London dispersion forces, as revealed by theoretical calculations using symmetry‐adapted perturbation theory (SAPT). Investigation of other GNs differing in nitrogen content, surface area, and pore sizes underscores the significance of nitrogen functional groups, defects, and interlayer nanochannels over the surface area in achieving superior selectivity. This work offers a new perspective on the design and fabrication of functionalized graphene derivatives, exhibiting superior noble gas storage and separation activity exploitable in gas production technologies.

Šedajová, Veronika↗