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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

An inverse vulcanized conductive polymer for Li–S battery cathodes

Polymers with a broad range of properties, structural diversity, and mechanical flexibility have been adopted in all aspects of Li–S batteries. However, currently explored polymers for Li–S cathodes suffer from low conductivity, low S content, and poor cycling performance. In this first-principles study, we theoretically design a new polymer, poly(2-vinyl,1,4-phenylene sulfide), by modifying the conductive poly(1,4-phenylene sulfide) via the vinyl group to enhance its ability to vulcanize with element S. Furthermore, we compare the properties of the experimentally realized sulfur vulcanized polymers via condensation and our designed sulfur vulcanized polymers via crosslinking as Li–S battery cathodes, in terms of gravimetric and specific capacities, as well as structural stability during the lithiation. Overall, we find that our designed polymer possesses better conductivity, higher specific capacity and gravimetric energy density, and better kinetic stability, and restricts the shuttle effect more efficiently than the current experimentally explored one. Also, the cross-linked sulfur compounds can be activated efficiently due to the short transport lengths rather than dissolution in the electrolyte during battery operation. Therefore, we believe our designed polymer cathode is promising for practical applications.

25 ENERGY STORAGE↗
DOE OSTI2021

A stable corridor for toroidal plasma compression

In this study, a toroidal plasma compressed by a collapsing flux conserver is analyzed to reveal stable scenarios of operation to high compression ratios. The resistive and ideal MHD stability is calculated in full toroidal geometry, using the asymptotic matching method in realistic conditions, and comparing with nonlinear simulations. The near edge current profile, controlled by toroidal field ramping during compression, is shown to be critical to stability due to coupling between poloidal components of the least stable mode. The extension of a length of shaft on axis is also found to be critical at high compression, as the resulting good curvature region in magnetic field stabilizes pressure driven modes that would otherwise be unstable. This work extends from previous studies, which initially showed the existence of a stable scenario, to include findings of more extensive stable zones, detailed effects of geometry, and nonlinear simulations of the instabilities. The nonlinear simulations of the compression are consistent with the linear analyses, confirming both the conservation and stability properties.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Electrical and thermal characteristics of LaB6 thermionic hollow cathodes operating in He, D2, Ar, and Xe at 4–200 Pa and 0.25–5 A cm−2

We report characteristics of lanthanum hexaboride (LaB6) cathodes for conditions relevant to a high-voltage, high-current switching device. LaB6 is selected because of its relatively low work function, stability in the presence of many common gas impurities, and a low evaporation rate (long life) at operating temperatures. We have investigated the effect of cathode geometry, gas type, pressure, and current on a LaB6 hollow cathode in a diode configuration with an opposing planar anode. The gas is stagnant at a relatively low pressure of 4–200 Pa (0.03–1.5 Torr) because of device high-voltage standoff requirements. In all cases, the plasma voltage decreases to a plateau value with increasing current where a practical device would operate. The plateau voltage aligns with the fill gas excitation or ionization voltage, depending on conditions. At high current, the cathode temperature exceeds that required for thermionic emission to supply the total current, a behavior that is understood by accounting for back-diffusing bulk electrons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Organic thin-film transistors with a bottom bilayer gate dielectric having a low operating voltage and high operational stability

This study reports on p-channel bottom-gate organic thin-film transistors (OTFT) that achieve low-voltage operation with a thin bilayer gate dielectric of CYTOP/HfO 2 that also leads to high operational stability. A bottom-gate geometry allows the thickness of the gate dielectric to be reduced to 17 nm, thereby increasing the gate dielectric capacitance density to a value of up to 258 nF/cm 2 . All OTFTs yielded threshold voltages (V TH ) lower than -1 V, thereby providing minimum operating voltage (gate to source voltage ~ V TH ) of -1 V with field-effect mobility values in the range from 0.3 to 0.8 cm 2 /Vs and subthreshold swing values below 100 mV/dec. Operational stability during DC bias stress was found similar to that measured in devices with a top-gate geometry, with about 1% of drain current change after 6 h. Here, using a double-stretched exponential function, the operational stability characteristics were modeled. It was found that by increasing the metal oxide layer thickness, the threshold voltage can shift toward positive values under DC stress tests. For CYTOP layer thicknesses above 15 nm, a thicker CYTOP layer was found to shift the threshold voltage in the opposite direction toward negative values. Furthermore, these p-channel bottom-gate organic transistor with a bilayer gate dielectric of CYTOP/HfO 2 combine high mobility, high operational stability, and lower voltage operation of -1 V compared to top-gate OTFTs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Solving Recent Challenges for Wrought Ni-Base Superalloys

This paper reviews the status of technology in design and manufacture of new wrought 21 polycrystalline Ni-base superalloys for critical engineering applications. There is a strong 22 motivation to develop new alloys that are capable of operating at higher temperatures to 23 realise improvements in thermal efficiency, which are necessary to achieve environmental 24 targets for reduced emissions of harmful green-house gases. From the aerospace sector, 25 the development of new powder metallurgy and ingot metallurgy alloys are discussed for 26 disk rotor and static applications. New compositions for powder metallurgy contain about 27 50-55% of gamma prime (γ') strengthening precipitates to ensure components operate 28 successfully at temperatures up to 788°C (1450°F). In contrast, new compositions for ingot 29 metallurgy aim to occupy a design space in temperature capability between Alloy 718 and 30 current powder alloys that are in-service, and show levels of γ' of about 30-44%. The focus 31 in developing these alloys was design for manufacturability. To complement the aerospace 32 developments, a review of work to understand the suitability of candidate alloys for multiple 33 applications in Advanced-Ultra Supercritical (AUSC) power plants has been undertaken by 34 Detrois, Jablonski and Hawk from the National Energy Technology Laboratory. In these 35 power plants, steam temperatures are required to reach 700-760°C. The common thread is 36 to develop alloys that demonstrate a combination of high temperature properties, which are 37 reliant on both the alloy composition and microstructure and can be produced readily at the 38 right price. For the AUSC applications, the emphasis is on high temperature strength, long 39 term creep life, phase stability, oxidation resistance and robust welding for fabrications. 40 Whereas for powder disk rotors in aircraft engines, the priority is enhanced resistance to 41 time dependent crack growth, phase stability and resistance to environmental damage, while 42 extending the current strength levels, which are shown by existing alloys, to higher 43 temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High-Throughput Discovery Illuminates Design Principles and Limits for Long-Lived Charged Species in Organic Electrolytes

The chemical stability of charged molecules in all-organic redox flow batteries (RFBs) is required for the prolonged operation of these devices. Molecular engineering and electrolyte optimization are used to mitigate parasitic reactions and extend the lifetimes of the charge carriers. However, how much can structural variation extend the lifetime? To probe this query, we designed a high-throughput kinetic study of the radical cation of N-methylphenothiazinium, guided by statistical sampling and learning algorithms. Using Argonne’s autonomous discovery facility, we conducted over 6,000 kinetic experiments with robotic sample preparation, parallel kinetic measurements, and machine learning inputs, testing 188 solvent molecules selected from a space of over 540 candidates from 11 chemical classes. Algorithmic selections guided us to stable solvent candidates, which were further tested in high concentration with and without supporting electrolyte. Our findings reveal the inherent difficulty of exceeding the current state of the art through solvent variation. The desired stability is statistically rare and poorly predictable. Among the many tested, only three solvents significantly outperformed our baseline, acetonitrile─and none by more than a factor of 3─suggesting a general challenge in achieving the necessary techno-economic targets. Furthermore, we suggest that self-discharge through solvent homolysis is the cause of the observed limitations. Several structural motifs contribute to >1,000 h half-life stability including molecular simplicity, symmetry, oxidation complement, and strategic fluorination. Importantly, this workflow establishes effective assays for diagnosing and predicting oxidative stress for highly stable liquid electrolytes in all batteries.

Batteries↗
DOE OSTI2021

CO2 Electrolyzer to Produce Formic Acid at Industry Relevant Current Density

Electrochemical CO2 reduction reaction (CO2RR) to produce formic acid has attracted great interest recently since formic acid can be used as a feedstock for biorefineries. Over the past decade, much effort has been devoted to the prospects of electrochemical CO2 conversion to formic acid. However, issues including low current density, low selectivity, low energy efficiency, poor long-term stability, and production of formate salts instead of formic acid remain as the great challenges for the development and commercialization of this technology. Recently, Dioxide Materials (DM) has developed an electrolyzer technology that can directly convert CO2 to pure formic acid with a three-compartment CO2 electrolyzer. In this work, DM will present our recent effort on improving the electrolyzer performance operating at industry relevant current density (200 mA/cm2). We have demonstrated 200 mA/cm² with 80% Faradaic efficiency for 1000 hours of operation. The effects of CO2 concentration and impurities in the flue gas on the electrolyzer performance will be discussed, as will ongoing efforts to test the device at a coal fired power plant. The long-term (1000 h) performance of the electrolyzer will also be presented.

Yang, Hongzhou↗
DOE OSTI2024

Nano Scale Poly(vinylidene chloride-co-acrylonitrile) Protection for Reversible and Stable Mg Anode Interface

This study investigates the efficacy of a polymer coating, PVdC-co-AN, in enhancing the stability and reversibility of the electrochemical Mg anode interface. Coated electrodes, immersed in a 0.25 M Mg(TFSI) 2 −0.50 M MgCl 2 /dimethoxyethane (DME) electrolyte, exhibit notable improvements. Cyclic voltammetry demonstrates consistent behavior with the coated electrode, while the uncoated electrode changes dramatically. During extended open circuit potential conditions, the coated electrode maintains much higher coulombic efficiency (93%) compared to the uncoated electrode (62%). Galvanostatic cycling test over 200 cycles further show the benefits of the PVdC-co-AN coating, decreasing the overpotential of Mg plating and improving long-term stability. The coated electrodes also demonstrate improved rate capability at higher current densities. Surface analysis reveals differences in the formation of byproducts between the coated and uncoated electrodes, indicating a more stable and uniform interface in the former. Nuclear magnetic resonance (NMR) spectroscopy suggests that the polymer influences ion mobility through tuning the solvation environments which results in better kinetics and fewer byproducts. In summary, the study affirms that the PVdC-co-AN coating significantly improves the stability and performance of Mg electrochemistry, offering a promising advancement for practical battery applications.

25 ENERGY STORAGE↗
DOE OSTI2021

Meron, skyrmion, and vortex crystals in centrosymmetric tetragonal magnets

The recent experimental confirmation of a transformation between meron and skyrmion topological spin textures in the chiral magnet Co 8 Zn 9 Mn 3 confirms that the skyrmion crystals discovered in 2009 are just the tip of the iceberg. Crystals of topological textures, including skyrmions, merons, vortices, and monopoles, can be stabilized by combining simple physical ingredients, such as lattice symmetry, frustration, and spin anisotropy. The current challenge is to find the combinations of these ingredients that produce specific topological spin textures. In this work, we report a simple mechanism for the stabilization of meron, skyrmion, and vortex crystals in centrosymmetric tetragonal magnets. In particular, the meron/skyrmion crystals can form even in absence of magnetic field. The application of magnetic field leads to a rich variety of topological spin textures that survive in the long wavelength limit of the theory. When conduction electrons are coupled to the spins, these topological spin textures twist the electronic wave functions to induce Chern insulators and Weyl semimetals for specific band filling fractions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Comparative Evaluation of the Single-Phase Shift and Extended-Phase Shift Control for Isolated DC-DC Converter

Abstract: This paper presents a comparative evaluation of the Single-Phase Shift (SPS) and Extended-Phase Shift (EPS) controls for the isolated DC-DC Converter. The analysis is based on the power regulation range, flexibility of operation, current stress on power devices, system efficiency while focusing on the issue of backflow power, control complexity, design and implementation overhead, and stability of the entire system. It is also examined how the backflow influences power circulation and increases current stress. Here, the Dual Active Bridge (DAB) Converter is employed to assess the performance of the control methods. Compared to SPS control, EPS offers a wider power regulation range, greater flexibility, lower current stress, and better system efficiency. However, EPS has increased control complexity, design and implementation overhead, and often requires sophisticated feedback control loops. The comparison is made through mathematical modeling of power transfer, backflow, and current stress. Simulation results validate the comparative analysis presented.

Amir, Aamir [The University of Alabama (UA)]↗
DOE OSTI2020

Electrochemical CO 2 Utilization: Scalable System Operation for Formic Acid Production

In recent years, research into the electrochemical reduction of CO 2 has grown exponentially. Formic acid (FA) has become a particular value product from CO 2 due to its versatility [1], optimal atom economy [2], and thermodynamic favorable [3]. FA can be produced electrochemically via a direct two-electron transfer process involving CO 2 with a proton source, requiring less energy input and fewer reaction steps than the conventional Kemira process. However, product selectivity, electrode stability, and low faradic efficiency due to increased resistance under constant current, remain key issues for CO 2 reduction to FA [4]. University of Kentucky’s Center for Applied Energy Research (UK CAER) is currently investigating reactor designs to address the challenges associated with electrochemical CO 2 conversion to FA [5]. The current reactor system employs: (1) an organic-based charge carrier which shuttles charge directly to the catalyst to enable CO 2 reduction to FA; (2) novel electrode materials to mitigate large voltages and improve conductivity; and (3) a flow system which not only allows for the volumetric scale-up of both charge carrier and catalyst, but also decouples the charger carrier re-energized and FA production processes to protect the catalyst’s stability due to overpotential. Through careful adjustment of electrode, charge carrier, and electrolyte selection, cell resistances have decreased by over 15%, facilitating conduction necessary for effective CO 2 reduction to FA. The system uses a highly specific engineered catalyst, which has produced over 100 mM FA at a rate of over 10 mM FA/hour following the aforementioned electrode/charge carrier changes. System design considerations (flow rate, bulk volume) and modeling of the system will also be discussed.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2025

Conformal high-entropy oxide coatings enable fast and durable surface oxygen reactions

Developing active and durable air electrodes for efficient oxygen reactions is challenging for protonic ceramic cells (PCCs), especially at temperatures below 550°C. Here, in this study, we report a rationally designed conformal coating with a high-entropy PrNi 0.2 Mn 0.2 Co 0.2 Fe 0.2 Cu 0.2 O 3−δ (PNMCFC) perovskite structure on the surface of a state-of-the-art PrBaCo 2 O 5+δ (PBC) air electrode. The formed hybrid air electrode (PNMCFC-PBC) shows faster surface oxygen kinetics and a more stable phase structure in high-humidity air than the bare PBC electrode. Further density functional theory calculations suggest that the conformal coating mitigates Ba segregation at the interface and improves oxygen-related reactions, enhancing overall stability and electrocatalytic performance. The cells with the developed hybrid electrodes show encouraging electrochemical performance at 550°C: a polarization resistance of 0.72 Ω cm 2 , a peak power density of 1.30 W cm −2 , an electrolysis current density of −1.36 A cm −2 at 1.3 V, and reasonable operating stabilities (∼200 h at 550°C).

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

An Aerosol Jet Printed Resistance Temperature Detector‐Micro Hotplate with Temperature Coefficient of Resistance Stabilized by Electrical Sintering

Abstract Aerosol jet printing (AJP) is an emerging direct write tool enabling rapid prototyping and fabrication of electronics components. AJP provides faster and less expensive production of devices with feature sizes of >10 microns compared to traditional MEMS processes. Herein, the fabrication of a resistance temperature detector‐micro hotplate (RTD‐µHP) is reported using AJP printed silver. AJP eliminates sophisticated MEMS processes such as masking, alignment, and etching. The compatibility of the AJP process with a broad range of materials is demonstrated by printing highly resolved lines on rigid and flexible substrates. Optimal thermal sintering conditions of AJP printed silver (Ag) lines are found by in situ resistance measurements. To stabilize the temperature coefficient of resistance (TCR) of the RTD‐µHP at high operating current levels, electrical sintering is performed on the RTD‐µHPs. Electrical sintering improves the conductivity of fully thermally sintered Ag RTD‐µHPs by 32% and provides a burn‐in mechanism for stabilizing the TCR. The TCR of the RTD‐µHPs after electrical sintering is 3.80 × 10 −3 at 22 °C, close to the value for bulk Ag. The performance of the RTD‐µHPs is tested using a reference thermocouple. The RTD‐µHPs show reliable and repeatable heating and temperature sensing up to 70 °C in air.

Sui, Yongkun↗
DOE OSTI2022

Using Lag Compensator in Orbit Feedback

Growing demand on the beam orbit stability requires higher loop gain inside the operational bandwidth. However, increasing the gain leads to the increase of the unity gain frequency and problems with systems stability due to the additional phase shifts caused by the trims (power supplies, eddy currents in vacuum chambers, etc.) and filtering of beam position data. Conventionally employed systems have 20 dB/decade slope near the unity gain providing 90 degrees phase shift which is sufficient for stability. Increase of the slope to 40 dB/decade by adding additional pole into the signal chain increases the phase shift to 180 degrees and makes system unstable. Utilizing one or more lag compensators allows to increase the gain while keeping phase margin acceptable. The paper provides more details on the proposed solution as well as simulations of how the transients will be modified.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Stable compression of a spherical tokamak plasma

In this study, an analysis of toroidal plasma compression by a collapsing flux conserver reveals linearly stable scenarios of operation to high compression ratios. The resistive and ideal MHD stability is calculated in full toroidal geometry using the asymptotic matching method in realistic conditions. A time dependent MHD simulation of the compression is conducted to confirm the conservation principles used to calculate the equilibrium states for the analysis. The near edge current profile, controlled by toroidal field ramping during compression, is shown to be critical to stability due to coupling between poloidal components of the least stable mode. Two cases with slight differences in edge current are examined, one with a stable corridor to high compression and one without.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Interplay of changing irrigation technologies and water reuse: example from the upper Snake River basin, Idaho, USA

Abstract. Careful allotment of water resources for irrigation is critical for ensuring the resiliency of agriculture in semiarid regions, and modernizing irrigation technology to minimize inefficient water losses is an important tool for farmers and agricultural economies. While modernizing irrigation technology can achieve reductions in the nonbeneficial use of water, such as bare soil evaporation and nonconsumptive losses, water returned to the landscape is also reduced, often eliminating flow paths that other users rely on. In basins using a combination of surface and groundwater, replenishing aquifer storage by the managed aquifer recharge (MAR) of seasonally available water can mitigate the aquifer drawdown that results from reduced recharge when irrigation efficiency is improved. We examine the effects of MAR on the system-scale efficiency of modernizing irrigation technology and the resulting changes in the reuse of nonconsumptive losses, using a macroscale hydrologic model applied to the semiarid upper Snake River basin (USRB) of western Wyoming and southern Idaho, USA. Irrigation technologies were represented explicitly in the model, and available data informed baseline parameterizations of the irrigation technology. A suite of parameterizations were simulated that updated the existing technologies to be more efficient, both with and without sufficient MAR to cause a stabilization of the aquifer at the present-day head. As expected, simulated changes in irrigation technology resulted in greater downstream export of pristine water and a higher rate of aquifer drawdown when MAR was not simulated. Under current water use and cropping patterns, we were not able to simulate aquifer stabilization and maintain discharge downstream at any level of irrigation efficiency. We found support for the hypothesis that, as efficiency improves, less MAR is required to maintain a stable aquifer than when return flows are reduced due to increased efficiency. To evaluate the hypothesis, we defined the management benefit as a metric that compared the difference between the change in irrigation's net recharge and the change in MAR required as irrigation technology became more efficient. The metric generally indicated that less MAR was needed than net recharge was lost, but only for the most efficient case did the management benefit exceed the MAR needed at the baseline to stabilize the aquifer. Increasing efficiency of irrigation technology reduced the reuse of the gross irrigation derived from prior nonconsumptive losses, but simulating MAR increased reuse for a given parameterization, leading to higher effective irrigation efficiency. We find that local groundwater storage that users depend on is generally more sensitive to management decisions than downstream flows, and the drawdown of the aquifer without MAR always exceeded any decrease in discharge induced by MAR. Improving resource sufficiency in semiarid systems like the USRB will require an array of solutions that will need to balance benefits to local and downstream users.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Physics basis for the reference flat-top plasma scenario in the ST–E1 fusion power plant

As part of the U.S. Department of Energy’s Milestone-Based Fusion Energy Development Program, Tokamak Energy has completed the pre-concept design of the ST–E1 fusion power plant. ST–E1 is envisaged to operate in two phases: a pilot plant phase, targeting sustained net power production of 300 - 500 MWe for a duration >1 hr, followed by a commercial power plant phase targeting steady-state operations and a normalised overnight capital cost of ⩽12 000 $\$$/kWe. The design process adopted was highly iterative, integrating all major plant systems and progressing in a phased fidelity approach. At the pre-conceptual stage, the emphasis has been on exploring the design space, identifying the main system-level trade-offs, and making the key decisions that define the overall plant concept, rather than optimising a single operating point. This paper, part of a focused collection detailing the ST–E1 pre-concept design, addresses the development of a series of reference flat-top plasma operating points for the pilot plant phase. A modelling workflow was established to develop and assess candidate plasma design points and explore key dependencies. The workflow includes integrated core plasma modelling, magnetohydrodynamic (MHD) stability assessment, equilibrium generation, scrape-off-layer and exhaust modelling, heating & current drive design and optimisation, and turbulent transport modelling. Using this framework, the impact of several key parameters on the flat-top operating space was investigated, including the density limit, core radiation fraction and divertor power loading, level of external heating and curent drive power and assumed pedestal characteristics. The MHD stability, controllability and micro-stability characteristics of these plasmas were also analysed. These investigations informed the definition of a set of fully non-inductive, flat-top reference operating points that satisfy the high-level ST–E1 mission, including a low and high density case, a case that is stable to resistive wall modes and a case with reduced divertor power loading.

ST–E1↗
DOE OSTI2022

Study of carbon nanotube embedded honey as a resistive switching material

In this paper, natural organic honey embedded with carbon nanotubes (CNTs) was studied as a resistive switching material for biodegradable nonvolatile memory in emerging neuromorphic systems. CNTs were dispersed in a honey-water solution with the concentration of 0.2 wt% CNT and 30 wt% honey. The final honey-CNT-water mixture was spin-coated and dried into a thin film sandwiched in between Cu bottom electrode and Al top electrode to form a honey-CNT based resistive switching memory (RSM). Surface morphology, electrical characteristics and current conduction mechanism were investigated. The results show that although CNTs formed agglomerations in the dried honey-CNT film, both switching speed and the stability in SET and RESET process of honey-CNT RSM were improved. The mechanism of current conduction in CNT is governed by Ohm’s law in low-resistance state and the low-voltage range in high-resistance state, but transits to the space charge limited conduction at high voltages approaching the SET voltage.

36 MATERIALS SCIENCE↗