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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 OSTI2021

Mass-conserving implicit–explicit methods for coupled compressible Navier–Stokes equations

Earth system models are composed of coupled components that separately model systems such as the global atmosphere, ocean, and land surface. While these components are well developed, coupling them in a single system can be a significant challenge. Computational efficiency, accuracy, and stability are principal concerns. In this study we focus on these issues. In particular, implicit–explicit (IMEX) tight and loose coupling strategies are explored for handling different time scales. For a simplified model for the air–sea interaction problem, we consider coupled compressible Navier–Stokes equations with an interface condition. Under the rigid-lid assumption, horizontal momentum and heat flux are exchanged through the interface. Several numerical experiments are presented to demonstrate the stability of the coupling schemes. Here, we show both numerically and theoretically that our IMEX coupling methods are mass conservative for a coupled compressible Navier–Stokes system with the rigid-lid condition

42 ENGINEERING↗
DOE OSTI2023

Directing High-Efficiency Na Plating with Carbon–Aluminum Junction Interfaces for Anode-Free Na Metal Batteries

Anode-free sodium metal batteries are highly promising for future energy storage but suffer from much faster cycling degradation as they are sensitive to even trace levels of irreversible side reactions. This work focuses on the most practical Al foil current collectors and systematically examined the effect of nano-sized carbon coating on improving the Na plating and stripping stability. We identified that the carbon-Al junction interface generated by carbon coating enabled more uniform Na depositing with lower overpotentials, delivering higher than 99.8% Faradaic efficiencies for a wide range of cycling currents between 0.5 and 3.0 mA cm -2 . This performance is much better than the 96.4% efficiency observed on uncoated Al foils under the same conditions, and was also confirmed under lean electrolyte and freezing electrolyte conditions, and can be attributed to the stronger interfacial binding and enhanced sodiophilic properties of the carbon-aluminum junction sites. Furthermore, these sites not only ensure uniform Na plating but also eliminates side reactions that would otherwise cause electrolyte depletion. As a result, Na-metal free full cells assembled with high capacity Na 3 V 2 (PO 4 ) 3 cathode delivered ~ 85% capacity retention for 100 cycles, higher than the 73% of retention of uncoated Al foil.

25 ENERGY STORAGE↗
DOE OSTI2022

Hydration-driven stabilization and volume collapse of grain boundaries in Mg2SiO4 forsterite predicted by first-principles simulations

Grain boundaries in mantle minerals are of critical importance to geophysical and geochemical processes of the Earth’s interior. One of the fundamental issues is to understand how the water (H 2 O) component influences the properties of grain boundaries in silicate materials. Here, we report the results of the structure and stability of several tilt grain boundaries in Mg 2 SiO 4 forsterite over the pressure range 0 to 15 GPa using density functional theory-based first-principles simulations. Here, the results suggest greater energetic stability and hydration-driven volume collapse (negative excess volume) at zero pressure for the majority of hydrous grain boundaries relative to the anhydrous (dry) ones. All the hydrous grain boundaries become increasingly favorable at elevated pressures as the calculated hydration enthalpy systematically decreases with increasing pressure. The hydrous components at the interfacial regions are predominantly in the hydroxyl form and, to a lesser extent, in the molecular H 2 O form. Their calculated ratio ranges from 1.6 to 8.7 among the different grain boundary configurations. Our structural analysis also reveals that the hydroxyls are bound to either both Mg and Si or to Mg only. In comparison, the molecular species are bound only to Mg sites. Besides direct oxygen-hydrogen bonding, intermolecular hydrogen bonding becomes important with compression. On the basis of our results, we suggest that local atomic rearrangements caused by dissociative adsorption of water facilitate efficient compaction of the boundary interfaces, which, in turn, results in greater relative stability of hydrous grain boundaries. This means that water prefers to be incorporated within the grain boundaries over the bulk of silicate materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Low-cost, Highly Efficient and Fast Thermally Pressed Scalable Carbon-based Planar Perovskite Solar Cells

This Final Technical Report summarizes work completed under Award Number DEEE0009833, titled "Low-cost, Highly Efficient and Fast Thermally Pressed Scalable Carbon-based Planar Perovskite Solar Cells." The project addressed the central technical problem that carbon-electrode perovskite solar cells (C-PSCs) can reduce electrode costs and improve environmental durability, but they have historically lagged noble-metalcontact devices due to poor carbon/perovskite contact, high carbon-electrode resistance, imperfect hole extraction, and insufficient operational stability. The Statement of Project Objectives (SOPO), therefore, required systematic engineering of thermally pressed carbon-based planar perovskite solar cells by improving the carbon/perovskite interface quality, improving carbon-electrode conductivity, and further increasing device stability. The work advanced understanding of carbon-based perovskite photovoltaics by connecting device performance to three coupled mechanisms: interfacial recombination at the perovskite/hole-transport-layer/carbon stack; lateral and vertical transport losses in carbon contacts; and instability driven by moisture, heat, illumination, ion migration, and slow/variable manufacturing steps.

14 SOLAR ENERGY↗
DOE OSTI2021

Microwave-Assisted Synthesis of Cu@IrO 2 Core-Shell Nanowires for Low-Temperature Methane Conversion

A facile microwave-assisted synthesis was developed for the tunable fabrication of a novel Cu@IrO 2 core@shell nanowire motif. Experimental parameters, such as (i) reaction time, (ii) the method of addition of the Ir precursor, (iii) capping agent, (iv) reducing agent, as well as (v) the capping agent-to-reducing agent ratio, were subsequently optimized. The viability of other methods based on previously reported literature, such as refluxing, stirring, and physical sonication, was studied and compared with our optimized microwave-assisted protocol in creating our as-prepared materials. It should be noted that the magnitude of the IrO 2 shell could be tailored based on varying the Cu: Ir ratio coupled with judicious variations in the amounts of capping agent and reducing agent. Structural characterization techniques, such as XRD, XPS, and HRTEM (including HRTEM-EDS), were used to analyze our Cu@IrO 2 motifs. Specifically, the shell could be reliably tailored from sizes of 10 nm, 8 nm, 6 nm, and 3.5 nm with corresponding Cu: Ir ratios of 10:1, 15:1, 20:1, and 25:1, respectively. Moreover, the structural integrity of the motifs was probed and found to have been maintained after not only heat treatment but also the post-methane conversion process, indicative of an intrinsically high stability. Both components within the CuO-IrO 2 interface were able to activate methane at temperatures between 400 to 500 K with a reduction of the associated metal cations (Cu 2+ → Cu 1+ ; Ir 4+ → Ir 3+ ) and the deposition of CH x fragments on the surface, as clearly observed in the ambient-pressure XPS results. Thus, on the basis of their stability and chemical activity, these core-shell materials could be very useful for the catalytic conversion of methane into 'higher value" chemicals.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Work Function Tuning of a Weak Adhesion Homojunction for Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have demonstrated a comparable efficiency to Si-based cells. However, the buried interface with weak adhesion remains a critical issue since the ion migration enhanced by the built-in electric field at this interface might lead to instability. We report here that adjusting the energy-level alignment at the weak adhesion homojunction interface can mitigate ion migration and thereby enhance the stability and photovoltaic performance of PSCs. Functional molecules with self-assembled monolayer characteristics were introduced to the surface of the SnO2 layer using silane derivatives, which tuned the work function of the homojunction depending on the functional groups in the molecules and thereby significantly reduced the built-in electric field. The PSC exhibited a power conversion efficiency (PCE) of 25.3%. The maximum power point (MPP) tracking under continuous illumination confirmed that the device retained more than 97% of its initial PCE, even after 1,000 h.

homojunction↗
DOE OSTI2020

Suppressing Cation Migration in Triple-Cation Lead Halide Perovskites

Ion migration represents an intrinsic instability of metal halide perovskite solar cells. In this work, we show that triple-cation FA x MA y Cs 1–x–y PbI 3 [FA + = (NH 2 ) 2 CH + , MA + = CH 3 NH 3 + ] active layers with mixed orthorhombic, post-perovskite (δ ortho -CsPbI 3 ), and cubic perovskite (α) phases (i.e., α/δ-phase FA x MA y Cs 1–x–y PbI 3 ) exhibit improved cation stability against applied bias relative to pure α-phase perovskites (i.e., FA 0.85 Cs 0.15 PbI 3 and FA 0.76 MA 0.15 Cs 0.09 PbI 3 ). Infrared photothermal heterodyne imaging and time-of-flight secondary ion mass spectrometry are used to visualize exclusive α-phase perovskite lateral device A + cation accumulation (depletion) at perovskite negative (positive) electrode interfaces. The resulting compositional heterogeneities lead to degradation. Operational stability testing of solar cells reveals similar degradation behavior; α/δ-phase FA x MA y Cs 1–x–y PbI 3 lateral devices/solar cells, by contrast, show improved stabilities. Enhanced α/δ-FA x MA y Cs 1–x–y PbI 3 stability is rationalized by δortho-phase inclusions, acting as barriers through which A + cations do not easily migrate. This study thus provides new insights into cation migration in FA x MAyCs 1–x–y PbI 3 perovskites and suggests a materials design strategy toward suppressing cation instabilities in hybrid perovskites.

14 SOLAR ENERGY↗
DOE OSTI2025

Bulky Cation-Modified Interfaces for Thermally Stable Lead Halide Perovskite Solar Cells

Charged conjugated organic molecules offer promising prospects for reducing nonradiative recombination at interfaces in perovskite solar cells, while protecting the active layer from moisture. However, several studies have shown that the heat induced diffusion of these cations leads to irreversible solar cell degradation. Passivation molecules for perovskite can reconstruct the film surface into lower-dimensional phases when exposed to thermal stress, impeding charge extraction and affecting the photoconversion efficiency (PCE) of devices. In this work, we study how molecular interactions between passivation molecules and 3D CsFAPbI 3 perovskite impact stability and charge extraction at the perovskite/hole transport layer interfaces. Two model π- conjugated molecules are studied: 2-([2,2′-bithiophen]-5-yl)ethan-1-aminium iodide (2TI) and 2-(3‴,4′-dimethyl-[2,2′:5′,2″:5″,2‴- quaterthiophen]-5-yl)ethan-1-ammonium iodide (4TmI). We demonstrate that the speed of surface layer reconstruction under thermal stress can be controlled by the cation size and correlate these structural changes with the solar cell performance and stability. Devices treated with 2TI and 4TmI achieve PCEs over 21% and maintain their performance under thermal stress. Our findings demonstrate that thermal stability in PSCs can be achieved via the design engineering of passivation agents, offering a blueprint for developing next-generation passivation molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cooperative Research and Development Agreement between National Energy Technology Laboratory and University of Kentucky (Abstract)

The National Energy Technology Laboratory (NETL) and University of Kentucky (Participant) will collaborate in the development of “Deep Learning Potential-based Molecular Dynamics Simulation Investigation of Chemical Conversion-Absorption Coupling of CO 2 at Air-Reactive Deep Eutectic Solvent Interface.” This project is supported by DOE-Office of Science Graduate Student Research (SCGSR) program and managed by Oak Ridge Institute for Science and Education (ORISE). Deep eutectic solvents (DESs) are promising alternative sorbents for direct air capture (DAC) CO 2 due to their low vapor pressure, low corrosion, non-toxicity, relatively low cost, and biodegradable nature. Understanding the CO 2 reaction-transport mechanisms at the interface can help develop cost-effective DAC by DESs with high capacity and stability. The collaboration will investigate the absorption and chemical conversion of CO 2 at the air-DES interface to facilitate the development of novel DAC technology using reactive DESs. The anticipated results will make DAC more efficient, allow more sustainable use of our Nation’s fossil energy resources, and advance NETL’s ongoing CO 2 capture efforts.

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

Interfacial Water Manipulation with Ionic Liquids for the Oxygen Reduction Reaction

The role that interfacial water plays in both promoting and inhibiting the electrochemical oxygen reduction reaction (ORR) remains somewhat unclear and controversial. Here, we use electroanalytical chemistry, spectroscopy, and microkinetic modeling to probe the impact of hydrophobic ionic liquid (IL) thin films on interfacial water structure and its role in promoting or inhibiting the ORR. Through the use of in situ ATR-SEIRAS, we find that the IL thin films limit the content of water at the interface and prevent the formation of hydrogen bond stabilized water organization. The impact of this exclusion of water on the promotion of the ORR is through the reduced coverage of OH ad spectator species. The decreased solvation of “active” OH ad species weakens its interaction with the catalyst surface, lowering the barrier to the last step in the ORR mechanism. This “destabilized” OH ad impact on ORR kinetics is confirmed through a microkinetic model. Furthermore, the results presented here highlight the mechanistic pathway through which hydrophobic ILs enhance ORR kinetics and point to pathways to both further improve this performance enhancement and the potential for integration of hydrophobic ILs into other technologically relevant elementary electrochemical reactions.

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

Homo- and hetero-dimeric subunit interactions set affinity and efficacy in metabotropic glutamate receptors

Metabotropic glutamate receptors (mGluRs) are dimeric class C G-protein–coupled receptors that operate in glia and neurons. Glutamate affinity and efficacy vary greatly between the eight mGluRs. The molecular basis of this diversity is not understood. We used single-molecule fluorescence energy transfer to monitor the structural rearrangements of activation in the mGluR ligand binding domain (LBD). In saturating glutamate, group II homodimers fully occupy the activated LBD conformation (full efficacy) but homodimers of group III mGluRs do not. Strikingly, the reduced efficacy of Group III homodimers does not arise from differences in the glutamate binding pocket but, instead, from interactions within the extracellular dimerization interface that impede active state occupancy. By contrast, the functionally boosted mGluR II/III heterodimers lack these interface ‘brakes’ to activation and heterodimer asymmetry in the flexibility of a disulfide loop connecting LBDs greatly favors occupancy of the activated conformation. Our results suggest that dimerization interface interactions generate substantial functional diversity by differentially stabilizing the activated conformation. This diversity may optimize mGluR responsiveness for the distinct spatio-temporal profiles of synaptic versus extrasynaptic glutamate.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Low resistance p-type contacts to monolayer WSe2 through chlorinated solvent doping

Tungsten diselenide (WSe 2 ) is a promising p-type semiconductor limited by high contact resistance (R C ) and the lack of a reliable doping strategy. Here, we demonstrate that exposing WSe 2 to chloroform provides simple and stable p-type doping. In monolayer WSe 2 transistors with Pd contacts, chloroform increases the maximum hole current by over 100× (>200 µA/µm), reduces R C to ~ 2.5 kΩ·μm, and retains an on/off ratio of 10 10 at room temperature. These improvements persist for over 8 months, survive a 150 °C thermal anneal, and remain effective down to 10 K, enabling a cryogenic R C of ~ 1 kΩ·μm. Density functional theory indicates that chloroform strongly physisorbs to WSe 2 , inducing hole doping with minimal impact on the electronic states between the valence band and conduction band edges. Auger electron spectroscopy and atomic force microscopy suggest that chloroform intercalates at the WSe 2 interface with the gate oxide, contributing to doping stability and mitigating interfacial dielectric disorder, though further studies are needed to conclusively confirm this mechanism. This robust, scalable approach enables high-yield WSe 2 transistors with good p-type performance.

42 ENGINEERING↗
DOE OSTI2024

Kainate receptor channel opening and gating mechanism

Kainate receptors, a subclass of ionotropic glutamate receptors, are tetrameric ligand-gated ion channels that mediate excitatory neurotransmission. Kainate receptors modulate neuronal circuits and synaptic plasticity during the development and function of the central nervous system and are implicated in various neurological and psychiatric diseases, including epilepsy, depression, schizophrenia, anxiety and autism. Although structures of kainate receptor domains and subunit assemblies are available, the mechanism of kainate receptor gating remains poorly understood. Here we present cryo-electron microscopy structures of the kainate receptor GluK2 in the presence of the agonist glutamate and the positive allosteric modulators lectin concanavalin A and BPAM344. Concanavalin A and BPAM344 inhibit kainate receptor desensitization and prolong activation by acting as a spacer between the amino-terminal and ligand-binding domains and a stabilizer of the ligand-binding domain dimer interface, respectively. Channel opening involves the kinking of all four pore-forming M3 helices. Our structures reveal the molecular basis of kainate receptor gating, which could guide the development of drugs for treatment of neurological disorders.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Phase segregation reversibility in mixed-metal hydroxide water oxidation catalysts

Achieving stable, low-cost electrocatalysts represents a daunting challenge towards practical water oxidation reactions. Here, we report that a degraded electrocatalyst can be revivified under catalytic operating conditions by manipulating reversible phase segregation. Under the oxygen evolution reaction conditions, Fe segregation develops in the Ni–Fe hydroxide host lat- tice, with the formation of FeOOH, resulting in an interface between the FeOOH and the host lattice. A dynamic metal dissolu- tion–redeposition process accelerates the Fe segregation and formation of the FeOOH secondary phase, resulting in catalyst deactivation. Operando synchrotron spectroscopic and microscopic analyses suggest that the phase segregation is revers- ible between the water oxidation potential and the catalyst reduction potential. Therefore, we have developed an intermittent reduction methodology to revivify the catalytic activity under the operating conditions, enhancing catalyst durability. The pres- ent study highlights that tailoring phase segregation at the catalyst/electrolyte interface constitutes an important strategy for revivifying and stabilizing catalytic activity.

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

Cardiac troponin T N-domain variant destabilizes the actin interface resulting in disturbed myofilament function

Missense variant Ile79Asn in human cardiac troponin T (cTnT-I79N) has been associated with hypertrophic cardiomyopathy and sudden cardiac arrest in juveniles. cTnT-I79N is located in the cTnT N-terminal (TnT1) loop region and is known for its pathological and prognostic relevance. A recent structural study revealed that I79 is part of a hydrophobic interface between the TnT1 loop and actin, which stabilizes the relaxed (OFF) state of the cardiac thin filament. Given the importance of understanding the role of TnT1 loop region in Ca 2+ regulation of the cardiac thin filament along with the underlying mechanisms of cTnT-I79N-linked pathogenesis, we investigated the effects of cTnT-I79N on cardiac myofilament function. Transgenic I79N (Tg-I79N) muscle bundles displayed increased myofilament Ca 2+ sensitivity, smaller myofilament lattice spacing, and slower crossbridge kinetics. These findings can be attributed to destabilization of the cardiac thin filament’s relaxed state resulting in an increased number of crossbridges during Ca 2+ activation. Additionally, in the low Ca 2+ -relaxed state (pCa8), we showed that more myosin heads are in the disordered-relaxed state (DRX) that are more likely to interact with actin in cTnT-I79N muscle bundles. Dysregulation of the myosin super-relaxed state (SRX) and the SRX/DRX equilibrium in cTnT-I79N muscle bundles likely result in increased mobility of myosin heads at pCa8, enhanced actomyosin interactions as evidenced by increased active force at low Ca 2+ , and increased sinusoidal stiffness. These findings point to a mechanism whereby cTnT-I79N weakens the interaction of the TnT1 loop with the actin filament, which in turn destabilizes the relaxed state of the cardiac thin filament.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Structural inversion asymmetry in epitaxial ultrathin films of Bi(111)/InSb(111)B

Bismuth (Bi) films hold potential for spintronic devices due to strong spin-orbit coupling. Understanding the growth, surface states, and interactions with the substrate is key to their functionalization. Large-area high-quality (111) Bi ultrathin films were grown on InSb (111)B substrates by molecular beam epitaxy (MBE). Strong film-substrate interactions epitaxially stabilize the (111) orientation and lead to nonequivalent interface potentials. Analysis of angle-resolved photoemission spectroscopy (ARPES) measurements, employed to characterize the evolution of the surface states with film thickness, indicate a crossing at the $\overline{M}$ point, suggesting a topologically trivial phase in the thin film. In conclusion, the results show the presence of interfacial bonds to the substrate breaks inversion symmetry, preventing the semimetal-to-semiconductor transition predicted for freestanding bismuth layers, highlighting the importance of controlled functionalization and surface passivation of two-dimensional materials.

Inbar, Hadass S. [Univ. of California, Santa Barba↗
DOE OSTI2021

Two-Phase Turbulence Statistics from High Fidelity Dispersed Droplet Flow Simulations in a Pressurized Water Reactor (PWR) Sub-Channel with Mixing Vanes

In the dispersed flow film boiling regime (DFFB), which exists under post-LOCA (loss-of-coolant accident) conditions in pressurized water reactors (PWRs), there is a complex interplay between droplet dynamics and turbulence in the surrounding steam. Experiments have accredited particular significance to droplet collision with the spacer-grids and mixing vane structures and their consequent positive feedback to the heat transfer recorded in the immediate downstream vicinity. Enabled by high-performance computing (HPC) systems and a massively parallel finite element-based flow solver—PHASTA (Parallel Hierarchic Adaptive Stabilized Transient Analysis)—this work presents high fidelity interface capturing, two-phase, adiabatic simulations in a PWR sub-channel with spacer grids and mixing vanes. Selected flow conditions for the simulations are informed by the experimental data found in the literature, including the steam Reynolds number and collision Weber number (Wec={40,80}), and are characteristic of the DFFB regime. Data were collected from the simulations at an unprecedented resolution, which provides detailed insights into the continuous phase turbulence statistics, highlighting the effects of the presence of droplets and the comparative effect of different Weber numbers on turbulence in the surrounding steam. Further, axial evolution of droplet dynamics was analyzed through cross-sectionally averaged quantities, including droplet volume, surface area and Sauter mean diameter (SMD). The downstream SMD values agree well with the existing empirical correlations for the selected range of Wec. The high-resolution data repository from the simulations herein is expected to be of significance to guide model development for system-level thermal hydraulic codes.

Saini, Nadish↗