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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Evidence for correlation effects in noncentrosymmetric type-II Weyl semimetals

Topological fermions have mainly been addressed in the limit of weakly correlated systems, while the realization of Kondo-like physics arising from Dirac-Weyl fermions and implying strong correlations is rare. The noncentrosymmetric Weyl fermion R AlGe compounds (with R = La and Ce) provide a promising playground for revealing the impact of electronic correlations driven by f-electron states on Weyl fermions. Here, we tackle their charge dynamics as a function of temperature. Besides spotting typical optical signatures of a type-II Weyl semimetal in both materials, we discover that electronic correlations at low temperatures renormalize the nontrivial bands hosting the Weyl nodes and lead to a reduction of the Fermi velocity as well as an enhancement of the charge carriers effective mass in CeAlGe with respect to LaAlGe, both being a fingerprint of a so-called Weyl-Kondo system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Metal–Nitrogen–Carbon Cluster–Decorated Titanium Carbide is a Durable and Inexpensive Oxygen Reduction Reaction Electrocatalyst

Clusters of nitrogen- and carbon-coordinated transition metals dispersed in a carbon matrix (e. g., Fe-N-C) have emerged as an inexpensive class of electrocatalysts for the oxygen reduction reaction (ORR). In this work, it was shown that optimizing the interaction between the nitrogen-coordinated transition metal clusters embedded in a more stable and corrosion-resistant carbide matrix yielded an ORR electrocatalyst with enhanced activity and stability compared to Fe-N-C catalysts. Utilizing first-principles calculations, an electrostatics-based descriptor of catalytic activity was identified, and nitrogen-coordinated iron (FeN 4 ) clusters embedded in a TiC matrix were predicted to be an efficient platinum-group metal (PGM)-free ORR electrocatalyst. Guided by theory, selected catalyst formulations were synthesized, and it was demonstrated that the experimentally observed trends in activity fell exactly in line with the descriptor-derived theoretical predictions. The Fe-N-TiC catalyst exhibited enhanced activity (20 %) and durability (3.5-fold improvement) compared to a traditional Fe-N-C catalyst. It was posited that the electrostatics-based descriptor provides a powerful platform for the design of active and stable PGM-free electrocatalysts and heterogenous single-atom catalysts for other electrochemical reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Crystallization of polarons through charge and spin ordering transitions in 1T-TaS 2

The interaction of electrons with the lattice in metals can lead to reduction of their kinetic energy to the point where they may form heavy, dressed quasiparticles—polarons. Unfortunately, polaronic lattice distortions are difficult to distinguish from more conventional charge- and spin-ordering phenomena at low temperatures. Here we present a study of local symmetry breaking of the lattice structure on the picosecond timescale in the prototype layered dichalcogenide Mott insulator 1T-TaS 2 using X-ray pair-distribution function measurements. We clearly identify symmetry-breaking polaronic lattice distortions at temperatures well above the ordered phases, and record the evolution of broken symmetry states from 915 K to 15 K. The data imply that charge ordering is driven by polaron crystallization into a Wigner crystal-like state, rather than Fermi surface nesting or conventional electron-phonon coupling. At intermediate temperatures the local lattice distortions are found to be consistent with a quantum spin liquid state.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Planning Optimization for Inductively Charged On-demand Automated Electric Shuttles Project at Greenville, South Carolina

Wireless charging technology presents an ideal fit for autonomous electric vehicles for realizing a fully automated system (vehicle and charger). This paper presents a planning optimization analysis for a pilot project of in-route wireless charging infrastructure serving fixed-route on-demand shared automated electric shuttles (SAESs) at Greenville, South Carolina, USA. A single-objective non-linear mixed integer system planning optimization problem is formulated. A comprehensive cost model representing the overall inductively charged SAESs system is developed, considering road construction, power electronics and materials, traction battery, and installation costs. The optimization problem is solved to determine the best combination of the system key design parameters (number and allocations of wireless chargers, charging power level, track length and on-board battery capacity) that show the most cost-effective solution and allow the SAESs to achieve charge-sustaining operation. The planning platform incorporates representative simulated traffic data (driving speed and routes) for four SAESs in the Greenville using the Simulation of Urban Mobility tool. These data are fed to a vehicle powertrain model and a wireless charger power model to predict the battery power, energy and state-of-charge profiles, which are provided to the search algorithm to assess the design objectives under specific constraints. Finally, the results indicate that implementing high-power (100 kW) wireless charger at a few designated stops for fixed-route SAESs with the proper track length allows the vehicles to realize charge-sustaining operation, infinite range, and zero recharge downtime, with a significant reduction in the on-board battery (36%) and road coverage (69%), at minimum cost.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2021

Magnetohydrodynamic Control of Interfacial Degradation in Lithium-Ion Batteries for Fast Charging Applications

Interfacial anodic degradation in graphitic materials under fast charging conditions causes severe performance loss and safety hazard in lithium ion batteries. We present a novel method for minimizing the growth of these aging mechanism by application of an external magnetic field. Under magnetic field, paramagnetic lithium ions experience a magnetohydrodynamic force, which rotates the perpendicularly diffusing species and homogenizes the ionic transport. This phenomenon minimizes the overpotential hotspots at the anode/separator interface, consequently reducing SEI growth, lithium plating, and interfacial fracture. In situ electrochemical measurements indicate an improvement in capacity for lithium cobalt oxide/graphite pouch cell (20 mAh) charged from 1–5 C under an applied field of 1.8 kG, with a maximum capacity gain of 22% at 5C. Post-mortem FE-SEM and EDS mapping shows that samples charged with magnetic field have a reduced lithium deposition at 3C and a complete suppression of interfacial fracture at 5C. At 5C, a 24% reduction in the lithium content is observed by performing XPS on the anodic interfacial film. Finally, fast charging performance under variable magnetic field strengths indicate a saturation behavior in capacity at high fields (>2 kG), thereby limiting the field and consequent energy requirements to obtain maximum capacity gain under extreme conditions.

electromagnetism↗
DOE OSTI2025

Structural Tuning of Self‐Conductive Polymer as Gas Diffusion Layer for Electrocatalytic Reactions at High Current

Electrocatalytic conversions offer a promising route for sustainable chemical production using renewable energy. Gas diffusion layers (GDLs) enable selective product formation at high current densities but suffer from electrolyte flooding, and polytetrafluoroethylene (PTFE)-based GDLs typically require metal conductive layers, which constrain catalyst development. A recently developed GDL configuration, electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT)-coated PTFE, demonstrates notable flooding resistance, but suffers from gas diffusion limitations at elevated currents due to limited gas diffusion through the PEDOT layer. Here, different dopants in PEDOT are exploited to modify the physical properties and enhance gas transport. ClO 4 − -doped PEDOT exhibits superior performance due to optimized physical structure, leading to increased gas permeance and faradaic efficiency (FE) for CO production during electrocatalytic CO 2 reduction. Further optimization of coverage and thickness achieved by adjusting charge density led to an optimal configuration at 33 mC cm −2 . This GDL supports various metal electrocatalysts and demonstrates FE CO of > 90% for over 150 h at −200 mA cm −2 using a commercial silver electrocatalyst. This work highlights the importance of GDL engineering in enhancing performance and durability for long-term electrocatalytic processes.

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

Multi-objective sizing and dispatch for building thermal and battery storage towards economic and environmental synergy

The role of building thermal and battery storage is pivotal in advancing smart cities and achieving sustainability goals through effective energy management. Despite their significance, there are several limitations in the sizing approach and value stream analysis with various objectives for their widespread adoption in buildings. This work proposes a flexible and scalable multi-objective optimization framework for optimal sizing and dispatch of building thermal and battery storage, addressing conflicting objectives simultaneously using mixed-integer linear programming. The weighted-sum method is adapted, combining multiple objectives into a single function. The two-stage procedure iterates over different weights, generating optimal solutions and forming the Pareto front. Case studies are performed to assess the energy, economic, and environmental benefits of building energy storage systems for a large office building in three climate locations. The results demonstrate that the proposed framework efficiently determines optimal sizing and dispatch strategies, addressing the balance between economic viability and emission reduction. The dynamic relationship between time-of-use energy charges and emission factors leads to significantly different strategies based on whether economic or environmental concerns are prioritized. This research enhances our understanding of the benefits of TES and BES systems in buildings, providing valuable guidance to stakeholders.

25 ENERGY STORAGE↗
DOE OSTI2020

Fluorination effect for stabilizing cationic and anionic redox activities in cation-disordered cathode materials

We see that cation-disordered Li-excess cathodes with oxygen redox reactions are promising candidates for high-energy-density Li ion batteries. Nevertheless, the oxygen redox process that is required for the high capacity often comes with the oxygen loss, which leads to severe capacity degradation and voltage decay. In this work, we have successfully synthesized a series of Li-excess cation-disordered cathodes (Li 1.2 Mn 0.4+x Ti 0.4-x O 2-x Fx) (0 ≤ x ≤ 0.2) with different fluorine (F) contents. The electrochemical performance results show that the Li 1.2 Mn 0.55 Ti 0.25 O 1.85 F 0.15 (LMTOF0.15) exhibits the highest reversible capacity (275 mAh g -1 , under 30 mA g -1 ), cyclability, and voltage retentions. The mapping of resonant inelastic X-ray scattering (mRIXS) and differential electrochemical mass spectroscopy (DEMS) results reveal that the fluorination enhances the reversible lattice oxygen redox reaction while suppressing irreversible gas release and surface reactions. The X-ray Absorption Spectroscopy (XAS) during the initial two cycles shows that F-substitution alleviates the reduction of the Mn valence state during the whole (dis)charge processes in the bulk and at the surface of the material, results in higher average discharge voltage. In addition, the introduction of F improves the structural stability and suppresses local lattice distortion of the material. Therefore, LMTOF 0.15 is able to cycle with smaller polarization, less interfacial side reaction and Mn dissolution, and therefore results in enhanced cyclability. This work provides a comprehensive understanding of the fluorination effect on the cationic and anionic redox activities in cation-disordered Li-excess cathodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Electrochemical Structure of the Plasma–Liquid Interface

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

Absorption↗
DOE OSTI2020

Probing Depth-Dependent Transition-Metal Redox of Lithium Nickel, Manganese, and Cobalt Oxides in Li-Ion Batteries

Layered lithium nickel, manganese, and cobalt oxides (NMC) are among the most promising commercial positive electrodes in the past decades. Understanding the detailed surface and bulk redox processes of Ni-rich NMC can provide useful insights into material design options to boost reversible capacity and cycle life. Both hard X-ray absorption (XAS) of metal K-edges and soft XAS of metal L-edges collected from charged LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) showed that the charge capacity up to removing ~0.7 Li/f.u. was accompanied with Ni oxidation in bulk and near the surface (up to 100 nm). Of significance to note is that nickel oxidation is primarily responsible for the charge capacity of NMC622 and 811 up to similar lithium removal (~0.7 Li/f.u.) albeit charged to different potentials, beyond which was followed by Ni reduction near the surface (up to 100 nm) due to oxygen release and electrolyte parasitic reactions. Overall, this observation points toward several new strategies to enhance reversible redox capacities of Ni-rich and/or Co-free electrodes for high-energy Li-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Probing compactified extra dimensions with gravitational waves

We study the effect of compact extra dimensions on the gravitational wave luminosity and waveform. We consider a toy model, with a compactified fifth dimension, and matter confined on a brane. We work in the context of five-dimensional (5D) general relativity, though we do make connections with the corresponding Kaluza-Klein effective 4D theory. We show that the luminosity of gravitational waves emitted in 5D gravity by a binary with the same characteristics (same masses and separation distance) as a 4D binary is 20.8% less relative to the 4D case, to leading post-Newtonian order. The phase of the gravitational waveform differs by 26% relative to the 4D case, to leading post-Newtonian order. Such a correction arises mainly due to the coupling between matter and dilaton field in the effective 4D picture and agrees with previous calculations when we set black holes’ scalar charges to be those computed from the Kaluza-Klein reduction. The above corrections to the waveform and the luminosity are inconsistent with the gravitational-wave and binary pulsar observations, and they thus effectively rule out the possibility of such a simple compactified higher dimensions scenario. We also comment on how our results change if there are several compactified extra dimensions and show that the discrepancy with 4D general relativity only increases.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Lattice QED in an external magnetic field: Evidence for dynamical chiral symmetry breaking

We simulate quantum electrodynamics (QED) in a strong constant homogeneous external magnetic field on a Euclidean space-time lattice using the rational hybrid Monte Carlo method, developed for simulating lattice quantum chromodynamics (QCD). Our primary goal is to measure the chiral condensate in the limit when the input electron mass m is zero. We observe a nonzero value, indicating that the external magnetic field catalyzes chiral symmetry breaking as predicted by approximate truncated Schwinger-Dyson methods. Such behavior is associated with dominance by the lowest Landau level which causes the effective dimensional reduction from 3 + 1 dimensions to 1 + 1 dimensions for charged particles (electrons and positrons) where the attractive forces of QED can produce chiral symmetry breaking with a dynamical electron mass and associated chiral condensate. Since our lattice simulations use bare (lattice) parameters, while the Schwinger-Dyson analyses work with renormalized quantities, direct numerical comparison will require renormalization of our lattice results. Published by the American Physical Society 2024

Kogut, J. B. (ORCID:000000030151548X)↗
DOE OSTI2023

CO 2 Hydrogenation: Na Doping Promotes CO and Hydrocarbon Formation over Ru/m-ZrO 2 at Elevated Pressures in Gas Phase Media

Sodium-promoted monoclinic zirconia supported ruthenium catalysts were tested for CO 2 hydrogenation at 20 bar and a H 2 :CO 2 ratio of 3:1. Although increasing sodium promotion, from 2.5% to 5% by weight, slightly decreased CO 2 conversion (14% to 10%), it doubled the selectivity to both CO (~36% to ~71%) and chain growth products (~4% to ~8%) remarkably and reduced the methane selectivity by two-thirds (~60% to ~21%). For CO 2 hydrogenation during in situ DRIFTS under atmospheric pressure, it was revealed that Na increases the catalyst basicity and suppresses the reactivity of Ru sites. Higher basicity facilitates CO 2 adsorption, weakens the C–H bond of the formate intermediate promoting CO formation, and inhibits methanation occurring on ruthenium nanoparticle surfaces. The suppression of excessive hydrogenation increases the chain growth probability. Decelerated reduction during H 2 -TPR/TPR-MS and H 2 -TPR-EXAFS/XANES at the K-edge of ruthenium indicates that sodium is in contact with ruthenium. A comparison of the XANES spectra of unpromoted and Na-promoted catalysts after H 2 reduction showed no evidence of a promoting effect involving electron charge transfer.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Ferroelectric capacitors and field-effect transistors as in-memory computing elements for machine learning workloads

Abstract This study discusses the feasibility of Ferroelectric Capacitors (FeCaps) and Ferroelectric Field-Effect Transistors (FeFETs) as In-Memory Computing (IMC) elements to accelerate machine learning (ML) workloads. We conducted an exploration of device fabrication and proposed system-algorithm co-design to boost performance. A novel FeCap device, incorporating an interfacial layer (IL) and$$\text {Hf}_{0.5}\text {Zr}_{0.5}\text {O}_2$$ Hf 0.5 Zr 0.5 O 2 (HZO), ensures a reduction in operating voltage and enhances HZO scaling while being compatible with CMOS circuits. The IL also enriches ferroelectricity and retention properties. When integrated into crossbar arrays, FeCaps and FeFETs demonstrate their effectiveness as IMC components, eliminating sneak paths and enabling selector-less operation, leading to notable improvements in energy efficiency and area utilization. However, it is worth noting that limited capacitance ratios in FeCaps introduced errors in multiply-and-accumulate (MAC) computations. The proposed co-design approach helps in mitigating these errors and achieves high accuracy in classifying the CIFAR-10 dataset, elevating it from a baseline of 10% to 81.7%. FeFETs in crossbars, with a higher on-off ratio, outperform FeCaps, and our proposed charge-based sensing scheme achieved at least an order of magnitude reduction in power consumption, compared to prevalent current-based methods.

Science & Technology - Other Topics↗
DOE OSTI2026

Polariton Control of Molecular Charge Transfer in Perylene Diimide Semiconductors

We report the modulation of molecular charge transfer in a bay-substituted perylene diimide derivative embedded in a planar distributed Bragg reflector microcavity. Angle-resolved reflectance spectra confirm the formation of upper and lower polaritons with clear Rabi splitting, indicating strong coupling between the cavity mode and molecular excitons. Using broadband transient absorption spectroscopy, we compare the ultrafast dynamics of cavity and non-cavity films. While excited-state absorption and stimulated emission pathways remain largely unchanged, kinetic modeling reveals a moderate increase in the charge transfer rate and yield under strong coupling. This enhancement is attributed to a reduction in the effective driving force via the formation of the lower polariton, placing the system deeper into the Marcus inverted regime. Our results demonstrate a promising non-chemical method leveraging cavity quantum electrodynamics to modulate charge separation processes in molecular semiconductors.

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

Pseudocapacitive Charge Storage in Electrochromic Transition-Metal Oxide Thin Films

Electrochromic pseudocapacitive transition-metal oxide materials, such as tungsten oxide, which combine fast response, high energy density, and optical effects, can play a significant role as energy storage materials. Here we investigate the electrochemical kinetics of thin films of tungsten oxide, which turn transparent to sky-blue color in the lithiated state due to the reduction of W 6+ to W 5+ . In this study, we investigated the charge density, charge transfer, ion diffusion, and interfacial behavior upon Li + insertion/de-insertion in WO 3 . The electrochromic thin film's pseudocapacitive and electrical double layer mechanism was differentiated based on the power-law. Faradaic diffusion-controlled process dominates over the surface capacitive behavior at scan rates below 40 mV s –1 . These films exhibit an areal charge density of around 100 mC cm –2 and a capacitance of 80 mF cm –2 , superior to most comparable electrochromic materials and supercapacitors. This work combines electrochromics and energy storage properties and provides a fundamental understanding of pseudocapacitive and electrochromic mechanisms in WO 3 .

25 ENERGY STORAGE↗
DOE OSTI2021

Design, synthesis and characterization of fused bithiazole- and dithiophene-based low bandgap thienylenevinylene copolymers

The structural rigidity of fused units in the polymer backbone, in addition to the resulting stabilizing effect of the quinoidal structure, and tunable electronic properties have played a key role in promoting highly-ordered π-stacking moieties, exhibiting promising charge carrier mobilities. The electron-deficient thiazole moiety shows high planarity and effective π–π stacking, which leads to the reduction in the energy levels of the highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO), and ideally enhances the electron charge mobility. Four heterocycle-based monomers BTzS, BTzSe, DTS, and DTG based on fused bithiazole and dithiophene units incorporated with sulfur, selenium, silicon, and germanium as the bridging atoms were synthesized and characterized. Here, the monomers were copolymerized with the electron-rich alkylated thienylenevinylene (TV) unit to afford copolymers P1–P4. The thermal, optical, and electrochemical properties and crystallinity of the copolymers were thoroughly investigated. Extensive OFET device optimization using different solvents and annealing temperatures resulted in the best charge mobility of 0.09 cm2 V –1 s –1 for the electron-deficient bithiazole BTzS copolymer P1 and 0.36 cm2 V –1 s –1 for the DTS copolymer P3.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗