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Results for “High current density”

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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

PERSISTENT CURRENT EFFECT IN 15-16 T NB3SN ACCELERATOR DIPOLES AND ITS CORRECTION

Nb3Sn magnets with operating fields of 15-16 T are considered for the LHC Energy Doubler and a future Very High Energy pp Collider. Due to large coil volume, high critical current density and large superconducting (SC) filament size the persistent current effect is very large in Nb3Sn dipoles al low fields. This paper presents the results of analysis of the persistent current effect in the 15 T Nb3Sn dipole demonstrator being developed at FNAL, and describes different possibilities of its correction including passive SC wires, iron shims and coil geometry.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Methods and systems for fabricating high quality superconducting tapes

An MOCVD system fabricates high quality superconductor tapes with variable thicknesses. The MOCVD system can include a gas flow chamber between two parallel channels in a housing. A substrate tape is heated and then passed through the MOCVD housing such that the gas flow is perpendicular to the tape's surface. Precursors are injected into the gas flow for deposition on the substrate tape. In this way, superconductor tapes can be fabricated with variable thicknesses, uniform precursor deposition, and high critical current densities.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Energy Systems Integration Partnerships: NREL + GINER ELX

At current levels of renewable generation there are already periods when the supply of electrical power significantly exceeds the level of demand. The wide penetration of renewable energy sources (RES) requires an energy storage solution which can include hydrogen generated via Polymer Electrolyte Membrane (PEM) electrolysis.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2019

Methods and systems for fabricating high quality superconducting tapes

An MOCVD system fabricates high quality superconductor tapes with variable thicknesses. The MOCVD system can include a gas flow chamber between two parallel channels in a housing. A substrate tape is heated and then passed through the MOCVD housing such that the gas flow is perpendicular to the tape's surface. Precursors are injected into the gas flow for deposition on the substrate tape. In this way, superconductor tapes can be fabricated with variable thicknesses, uniform precursor deposition, and high critical current densities.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Methods and systems for fabricating high quality superconducting tapes

An MOCVD system fabricates high quality superconductor tapes with variable thicknesses. The MOCVD system can include a gas flow chamber between two parallel channels in a housing. A substrate tape is heated and then passed through the MOCVD housing such that the gas flow is perpendicular to the tape's surface. Precursors are injected into the gas flow for deposition on the substrate tape. In this way, superconductor tapes can be fabricated with variable thicknesses, uniform precursor deposition, and high critical current densities.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Methods and systems for fabricating high quality superconducting tapes

An MOCVD system fabricates high quality superconductor tapes with variable thicknesses. The MOCVD system can include a gas flow chamber between two parallel channels in a housing. A substrate tape is heated and then passed through the MOCVD housing such that the gas flow is perpendicular to the tape's surface. Precursors are injected into the gas flow for deposition on the substrate tape. In this way, superconductor tapes can be fabricated with variable thicknesses, uniform precursor deposition, and high critical current densities.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Round superconductor wires

A round superconductor wire and method for fabricating same are disclosed. Embodiments are directed to a round superconductor wire including at least two superconductor tapes wound on a wire former. Each superconductor tape includes: bottom stabilizer and silver layers; substrate disposed above the bottom silver layer; buffer film stack disposed above the substrate; superconductor film disposed above the buffer film stack; top silver layer disposed above the superconductor film; and top stabilizer layer disposed above the top silver layer. At least one of the bottom stabilizer layer, bottom silver layer, substrate, buffer film stack, superconductor film, top silver layer, or top stabilizer layer is of a different width, thickness, or material composition in one of the superconductor tapes than in another of the superconductor tapes. These and other embodiments achieve a round superconductor wire having improved current density in high magnetic field applications when made in small diameters.

Majkic, Goran↗
DOE OSTI2024

Methods and systems for fabricating high quality superconducting tapes

An MOCVD system fabricates high quality superconductor tapes with variable thicknesses. The MOCVD system can include a gas flow chamber between two parallel channels in a housing. A substrate tape is heated and then passed through the MOCVD housing such that the gas flow is perpendicular to the tape's surface. Precursors are injected into the gas flow for deposition on the substrate tape. In this way, superconductor tapes can be fabricated with variable thicknesses, uniform precursor deposition, and high critical current densities.

Majkic, Goran↗
DOE OSTI2016

High electrochemical performances of hierarchical hydrangea macrophylla like NiCo{sub 2}O{sub 4} and NiCo{sub 2}S{sub 4} as anode materials for Li-ion batteries

Graphical abstract: Mesoporous hydrangea macrophylla like NiCo{sub 2}O{sub 4} and NiCo{sub 2}S{sub 4} have been fabricated, which present excellent electrochemical performances as anode materials for Li-ion batteries. - Highlights: • Hierarchical NiCo{sub 2}O{sub 4} is successfully fabricated. • Hierarchical NiCo{sub 2}S{sub 4} is prepared via sulfide anion exchange. • The hierarchical NiCo{sub 2}O{sub 4} and NiCo{sub 2}S{sub 4} exhibit good electrochemical properties. - Abstract: In this work, hierarchical hydrangea macrophylla like NiCo{sub 2}O{sub 4} has been synthesized by solvothermal method followed by calcination treatment in air. By using Na{sub 2}S as sulfur source, the NiCo{sub 2}O{sub 4} is converted into NiCo{sub 2}S{sub 4}. Such hierarchical NiCo{sub 2}O{sub 4} exhibits a high specific capacity and excellent cycling stability (928 mAh g{sup −1} at a current density of 100 mA g{sup −1} after 100 cycles). Even at high current density of 2000 mA g{sup −1}, the electrode still delivers a specific capacity of 371 mAh g{sup −1} after 50 cycles. When the NiCo{sub 2}S{sub 4} is used as anode materials for lithium-ion batteries, a high discharge capacity of 1204 mAh g{sup −1} can be achieved. Meanwhile, the NiCo{sub 2}S{sub 4} electrode displays good cycling stability and rate capability. The excellent electrochemical performances can be attributed to the unique porous structure, which can effectively reduce the diffusion length for lithium ions and electrons, and alleviate volume expansion during the charge-discharge processes.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Vacuum microelectronics for beam power and rectennas

Vacuum Microelectronic devices can be described as vacuum transistors or micro-miniature vacuum tubes, as one chooses. The fundamental reason behind this new technology is the very large current densities available from field emitters, namely as high as 10(8) A/sq cm. Array current densities as high as 1000 A/sq cm have been measured. Total electron transit times from source to drain for 1 micron feature size devices have been predicted to be about 150fs. This very short transit time implies the possibility of submillimeter wave transmitters and rectennas in devices which can operate with reasonably high voltages and which are small in size and are lightweight. In addition, they are expected to be extremely radiation hard and very temperature insensitive. That is, they are expected to have radiation hardness characteristics similar to vacuum tubes, and both the high temperature and low temperature limits should be determined by the package. That is, there should be no practical intrinsic temperature or carrier freezeout problems for devices based on metals or composites. But the technology is difficult to implement at the present time because it is based on 300 to 500 angstrom radius field emitters which must be relatively uniform. There is also the need to understand the non-equilibrium transport physics in the near-surface regions of the field emitters.

Gray, Henry F.↗
DOE OSTI2020

Novel platinum group metal-free catalyst ink deposition system for combinatorial polymer electrolyte fuel cell performance evaluation

Here, a new system for rapid and precise fabrication of polymer electrolyte fuel cell (PEFC) membrane-electrode assemblies (MEAs) is introduced to facilitate rapid testing and characterization of platinum group metal-free (PGM-free) catalysts, with minimal waste of materials, using commercial combinatorial hardware and multi-channel potentiostat. The commercial combinatorial system, designed for high-throughput catalyst activity evaluation (i.e., low overpotential and current densities) using gas-diffusion electrodes (GDEs), has been further developed to enable simultaneous evaluation of the high current density performance on air of twenty-five cathodes prepared by coating catalyst-ionomer inks directly onto the membrane using a newly-developed deposition system. A nanopipette or micropipette coupled to a precise peristaltic pump is being used for precise and even catalyst ink deposition onto the membrane in each of twenty-five circular electrodes with areas of <1 cm 2 and in the precise locations required by the commercial combinatorial MEA hardware. The automated ink deposition system is coupled with a custom-designed heated vacuum table mounted on a computer-controlled XY stage to prevent deformation of the membrane and electrode layers during ink deposition onto the membrane. This system was utilized to evaluate the impact of ionomer to catalyst ratio on the hydrogen-air fuel cell performance of the PGM-free catalyst.

25 ENERGY STORAGE↗
DOE OSTI2023

Synthesis of 2H/ fcc -Heterophase AuCu Nanostructures for Highly Efficient Electrochemical CO 2 Reduction at Industrial Current Densities

Structural engineering of nanomaterials offers a promising way for developing high-performance catalysts toward catalysis. However, the delicate modulation of thermodynamically unfavorable nanostructures with unconventional phases still remains a challenge. Here, in this study, the synthesis of hierarchical AuCu nanostructures is reported with hexagonal close-packed (2H-type)/face-centered cubic (fcc) heterophase, high-index facets, planar defects (e.g., stacking faults, twin boundaries, and grain boundaries), and tunable Cu content. The obtained 2H/fcc Au 99 Cu 1 hierarchical nanosheets exhibit excellent performance for the electrocatalytic CO 2 reduction to produce CO, outperforming the 2H/fcc Au 91 Cu 9 and fcc Au 99 Cu 1 . The experimental results, especially those obtained by in-situ differential electrochemical mass spectroscopy and attenuated total reflection Fourier-transform infrared spectroscopy, suggest that the enhanced catalytic performance of 2H/fcc Au 99 Cu 1 arises from the unconventional 2H/fcc heterophase, high-index facets, planar defects, and appropriate alloying of Cu. Impressively, the 2H/fcc Au 99 Cu 1 shows CO Faradaic efficiencies of 96.6% and 92.6% at industrial current densities of 300 and 500 mA cm -2 , respectively, as well as good durability, placing it among the best CO 2 reduction electrocatalysts for CO production. The atomically structural regulation based on phase engineering of nanomaterials (PEN) provides an avenue for the rational design and preparation of high-performance electrocatalysts for various catalytic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Growth of Lithium Dendrites and Globules through a Solid Block Copolymer Electrolyte as a Function of Current Density

The uncontrollable nonplanar electrodeposition of lithium is a significant barrier to the widespread adoption of high energy density rechargeable batteries with a lithium metal anode. A promising approach for preventing the growth of lithium dendrites is the use of solid polymer electrolytes with a high shear modulus. Current density is the key variable in the electrodeposition of lithium. The present study is the first attempt at quantifying the effect of current density on the geometry and density of dendrites and other protrusions during electrodeposition through a solid polymer electrolyte. The geometry and density of defects formed on the lithium electrode were determined by X-ray microtomography. The tomograms revealed protrusions on the electrodeposited lithium electrodes that were either globular or dendritic, or void defects. The range of current densities over which stable, planar deposition was observed is quantified. At higher current densities, globular protrusions were observed. At the highest current density, both globular and dendritic protrusions were observed. The areal density of protrusion defects increased sharply with current density, while the overall defect density is a weak function of current density. Finally, our work enables comparisons between the experimentally determined onset of nonplanar electrodeposition and prevailing theoretical predictions with no adjustable parameters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2007

Large-Area Permanent-Magnet ECR Plasma Source

A 40-cm-diameter plasma device has been developed as a source of ions for material-processing and ion-thruster applications. Like the device described in the immediately preceding article, this device utilizes electron cyclotron resonance (ECR) excited by microwave power in a magnetic field to generate a plasma in an electrodeless (noncontact) manner and without need for an electrically insulating, microwave-transmissive window at the source. Hence, this device offers the same advantages of electrodeless, windowless design - low contamination and long operational life. The device generates a uniform, high-density plasma capable of sustaining uniform ion-current densities at its exit plane while operating at low pressure [<10(exp -4) torr (less than about 1.3 10(exp -2) Pa)] and input power <200 W at a frequency of 2.45 GHz. Though the prototype model operates at 2.45 GHz, operation at higher frequencies can be achieved by straightforward modification to the input microwave waveguide. Higher frequency operation may be desirable in those applications that require even higher background plasma densities. In the design of this ECR plasma source, there are no cumbersome, power-hungry electromagnets. The magnetic field in this device is generated by a permanent-magnet circuit that is optimized to generate resonance surfaces. The microwave power is injected on the centerline of the device. The resulting discharge plasma jumps into a "high mode" when the input power rises above 150 W. This mode is associated with elevated plasma density and high uniformity. The large area and uniformity of the plasma and the low operating pressure are well suited for such material-processing applications as etching and deposition on large silicon wafers. The high exit-plane ion-current density makes it possible to attain a high rate of etching or deposition. The plasma potential is <3 V low enough that there is little likelihood of sputtering, which, in plasma processing, is undesired because it is associated with erosion and contamination. The electron temperature is low and does not vary appreciably with power.

Foster, John E.↗
DOE OSTI2021

Effects of Wire Diameter and Filament Size on the Processing Window of Bi-2212 Round Wire

High engineering critical current density (J E of 1300 A/mm 2 at 4.2 K and 15 T) in Bi-2212 round wire has been achieved through a partial melt, overpressure heat treatment process. J E varies strongly with processing conditions, particularly the maximum heat treatment temperature (T max ). Increasing T max results in longer time in the melt (defined as the time between when Bi-2212 melts on heating and when Bi-2212 begins to form on cooling), more bridging between the filaments, lower J E , and higher ac losses. A wide processing window with a large range of T max that has a nearly constant J E is desired for processing large coils with large thermal mass and significant thermal time constants that may make precise control over the desired temperature – time profiles uncertain. Accordingly, we wanted to explore broadening the T max window by controlling the Bi-2212 powder melting or wire architecture design. In this work, we report on studies of the performance variation with T max for two production wires with a filling factor of about 20% and 85 × 18 filaments where filament size was varied by changing the wire diameter, a process which also shortens the distance between filaments. We found that wires with smaller filament diameter (9 to 11 μm) showed a peak J E at the low end of T max and also a J E that was more sensitive to T max . A J E – T max plot showed a plateau J E (4.2 K, 5 T) of ~1100 A/mm 2 between T max of 886 and 894 °C for 1.0 and 1.2 mm wires, where J E is less sensitive to the wire diameter and T max . This J E plateau range is a preferred processing window for achieving high J E in coils.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Sn-MOF derived bimodal-distributed SnO2 nanosphere as a high performance anode of sodium ion batteries with high gravimetric and volumetric capacities

Highlights: • Sn-MOF is used to prepare a bimodal-distributed SnO{sub 2} nanosphere. • The SnO{sub 2} nanosphere reveals a high tap density of 2.42 g cm{sup −3}. • The SnO{sub 2} nanosphere exhibits both of high gravimetric and volumetric capacity. • Excellent performances relate to structural stability and high Na{sup +} diffusion rates. - Abstract: This paper reported a high tap density SnO{sub 2} nanosphere with bimodal sizes distribution, which derived from Sn-based metal-organic frameworks (Sn-MOF) precursors. When used as anodes for Na-ion batteries, the SnO{sub 2} nanosphere was demonstrated with a high reversible sodium storage capacity of 417 mAh g{sup −1} at a current density of 50 mA g{sup −1} after 100 cycles. Even at a high current density of 1200 mA g{sup −1}, a reversible capacity of 105 mAh g{sup −1} can be obtained. Additionally, regarding to the packed volumetric capacity, the SnO{sub 2} nanosphere electrode demonstrated a high value of around 970 mAh cm{sup −3}, can be considered as a high volumetric capacity anode material. The excellent electrochemical performance could be ascribed to aspects of structural stability, high packing density and high Na{sup +} diffusion rates of the SnO{sub 2} nanosphere electrode. This work provides a new pathway to prepared nanostructured SnO{sub 2} materials, and demonstrated a high performance anode material for Na-ion battery with great specific capacity and cycling performance.

25 ENERGY STORAGE↗
DOE OSTI2022

Integration of a high oxygen permeability ionomer into polymer electrolyte membrane fuel cell cathodes for high efficiency and power density

In this work, we present a study on the integration of a high oxygen permeability ionomer (HOPI) with high durability carbon supported platinum (Pt/C) catalysts to prepare cathode catalyst layers (CCLs) for polymer electrolyte membrane fuel cells (PEMFCs). A key motivation is the production of PEMFCs with high efficiency and durability for heavy-duty fuel cell vehicles. Our results from integrating a pre-commercial HOPI with robust, state-of-the-art catalysts with medium and low surface area carbon supports show significant increases in specific activities (67% increase over the standard commercial ionomer) at low current densities and reduced oxygen (O 2 ) transport resistances (R O2 ’s) at high current densities, enabling both higher efficiency and peak power density. The reduction in the R O2 with the HOPI is most significant at low relative humidity (RH), due to its more rigid backbone structure resisting compaction at lower water contents. In our ink optimization analysis, we show that the HOPI in this study achieves its peak performance with an ionomer to carbon ratio (I/C) of 0.6 and a moderately alcohol-rich ink solvent when fabricating catalyst layers by the decal method with an automatic wet film coater.

08 HYDROGEN↗
DOE OSTI2023

Molten Sodium Penetration in NaSICON Electrolytes at 0.1 A cm –2

High-conductivity solid electrolytes, such as the Na superionic conductor, NaSICON, are poised to play an increasingly important role in safe, reliable battery-based energy storage, enabling advanced sodium-based batteries. Coupled demands of increased current density (≥0.1 A cm –2 ) and low-temperature (<200 °C) operation, combined with increased discharge times for long-duration storage (>12 h), challenge the limitations of solid electrolytes. Here, we explore the penetration of molten sodium into NaSICON at high current densities. Previous studies of β"-alumina proposed that Poiseuille pressure-driven cracking (mode I) and recombination of ions and electrons within the solid electrolyte (mode II) are the two main mechanisms for Na penetration, but a comprehensive study of Na penetration in NaSICON is necessary, particularly at high current density. To further understand these modes, this work employs unidirectional galvanostatic testing of Na|NaSICON|Na symmetric cells at 0.1 A cm –2 over 23 h at 110 °C. Further, while galvanostatic testing shows a relatively constant yet increasingly noisy voltage profile, electrochemical impedance spectroscopy (EIS) reveals a significant decrease in cell impedance correlated with significant sodium penetration, as observed in scanning electron microscopy (SEM). Further SEM analysis of sodium accumulation within NaSICON suggests that mode II failure may be far more prevalent than previously considered. Further, these findings suggest that total (dis)charge density (mAh cm –2 ), as opposed to current density (mA cm –2 ), may be a more critical parameter when examining solid electrolyte failure, highlighting the challenge of achieving long discharge times in batteries using solid electrolytes. Together, these results provide a better understanding of the limitations of NaSICON solid electrolytes under high current and emphasize the need for improved electrode–electrolyte interfaces.

25 ENERGY STORAGE↗