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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Carbon Fiber Oxidation in 4D

The oxidation of carbon fibers at high temperatures is the primary degradation process in the thermal protection system of many hypersonic flight vehicles. Predicting the rate and the extent of oxidation is critical to ensure a safe and effective design. An oversized thermal protection system adds unnecessary mass, while an under-designed one risks system failure and mission loss. Resolving high-temperature material degradation due to oxidation has been a long-standing challenge in designing for re-entry flight environments. Using time-resolved in situ X-ray microtomography, the oxidation of carbon fibers at high temperatures is directly imaged, resolving the two limiting degradation regimes: diffusion- and reaction-limited. The ability to resolve material degradation in time at the sub-micron scale sheds light on the ablation phenomenon and enables predictions of material constitutive properties evolving in time, with profound implications on the ability to model the aerothermal response of heat shield materials in hostile environments.

ablation↗
DOE OSTI2024

Embedding Reverse Electron Transfer Between Stably Bare Cu Nanoparticles and Cation‐Vacancy CuWO 4

Cu nanoparticles (NPs) have attracted widespread attention in electronics, energy, and catalysis. However, conventionally synthesized Cu NPs face some challenges such as surface passivation and agglomeration in applications, which impairs their functionalities in the physicochemical properties. Here, the issues above by engineering an embedded interface of stably bare Cu NPs on the cation-vacancy CuWO 4 support is addressed, which induces the strong metal-support interactions and reverse electron transfer. Various atomic-scale analyses directly demonstrate the unique electronic structure of the embedded Cu NPs with negative charge and anion oxygen protective layer, which mitigates the typical degradation pathways such as oxidation in ambient air, high-temperature agglomeration, and CO poisoning adsorption. Kinetics and in situ spectroscopic studies unveil that the embedded electron-enriched Cu NPs follow the typical Eley-Rideal mechanism in CO oxidation, contrasting the Langmuir-Hinshelwood mechanism on the traditional Cu NPs. This mechanistic shift is driven by the Coulombic repulsion in anion oxygen layer, enabling its direct reaction with gaseous CO to form the easily desorbed monodentate carbonate.

Cu nanoparticles↗
DOE OSTI2023

Vapor Phase Infiltration Improves Thermal Stability of Organic Layers in Perovskite Solar Cells

Despite the rapid increase in power conversion efficiency (PCE) of perovskite solar cells (PSCs) over the past decade, stability remains a major roadblock to commercialization. Here, this work shows vapor phase infiltration (VPI) as a tool to create hybrid organic–inorganic layers that improve the stability of organic charge transport layers, such as hole-selective spiro-OMeTAD in PSCs and in other organic electronic devices. Using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and grazing incident wide-angle X-ray scattering (GIWAXS), we identify that infiltration of TiO x via VPI hinders the crystallization of the spiro-OMeTAD layer by likely preventing the π–π stacking of the molecules. Infiltrated PSCs retained more than 80% of their original efficiency after an operando stability test of 200 h at 75 °C, double the efficiency retained by devices without infiltration, in which the efficiency rapidly decreases in the first 50 h. This work provides a blueprint for using VPI to stabilize organic charge transport layers via prevention of π–π stacking leading to deleterious crystallization that shortens device lifetimes.

14 SOLAR ENERGY↗
DOE OSTI2021

Promoting Atomically Dispersed MnN 4 Sites via Sulfur Doping for Oxygen Reduction: Unveiling Intrinsic Activity and Degradation in Fuel Cells

Carbon supported and nitrogen coordinated single Mn site catalysts (Mn-N-C) catalysts are the most desirable platinum group metal (PGM)-free cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their insignificant Fenton reactions (vs. Fe), earth abundances (vs. Co) and encouraging activity and stability. However, current Mn-N-C catalysts suffer from high over-potential due to low intrinsic activity and less dense MnN 4 sites. Herein, we present sulfur-doped Mn-N-C catalyst (Mn-N-C-S) synthesized through an effective adsorption-pyrolysis process. Using electron microscopy and X-ray absorption spectroscopy (XAS) techniques, we verify the uniform dispersion of MnN 4 sites and confirm the effect of S doping on the Mn-N coordination. The Mn-N-C-S catalyst exhibits a favorable oxygen reduction reaction (ORR) activity in acidic media relative to the S-free Mn-N-C catalyst. The corresponding membrane electrode assembly (MEA) generated a remarkable performance with a peak power density of 500 mW cm -2 under a realistic H 2 /air environment. The constant voltage tests of fuel cells confirm the much-enhanced stability of the Mn-N-C-S catalyst compared to the Fe-N-C and Fe-N-C-S catalysts. The electron microscopy and Fourier transform XAS analysis provide insights into catalyst degradation associated with Mn oxidation and agglomeration. The theoretical calculation elucidates that the promoted ORR activity is mainly attributed to the spatial effect stemmed from the repulsive interaction between the ORR intermediates and adjacent S do-pants.

25 ENERGY STORAGE↗
DOE OSTI2022

Alkaline-Earth Chalcogenide Nanocrystals: Solution-Phase Synthesis, Surface Chemistry, and Stability

Increasing demand for effective energy conversion materials and devices has renewed interest in semiconductors comprised of earth-abundant and biocompatible elements. Alkaline-earth sulfides doped with rare earth ions are versatile optical materials. However, relatively little is known about controlling the dimensionality, surface chemistry, and inherent optical properties of the undoped versions of alkaline-earth monoand polychalcogenides. Here, we describe the colloidal synthesis of alkaline-earth chalcogenide nanocrystals through the reaction of metal carboxylates with carbon disulfide or selenourea. Systematic exploration of the synthetic phase space allows us to tune particle sizes over a wide range using a mixture of commercially available carboxylate precursors. Solid-state NMR spectroscopy confirms the phase purity of the selenide compositions. Surface characterization reveals that bridging carboxylates and amines preferentially terminate the surface of the nanocrystals. While these materials are colloidally stable in the mother solution, the selenides are susceptible to oxidation over time, eventually degrading to selenium metal through polyselenide intermediates. As part of these investigations, we have developed the colloidal syntheses of barium di- and triselenides, two among few reported nanocrystalline alkaline-earth polychalcogenides. Electronic structure calculations reveal that both materials are indirect band gap semiconductors. The colloidal chemistry presented here may enable the synthesis of more complex, multinary chalcogenide materials containing alkaline-earth elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A multi-technique approach to understanding delithiation damage in LiCoO2 thin films

Abstract We report on the delithiation of LiCoO 2 thin films using oxalic acid (C 2 H 2 O 4 ) with the goal of understanding the structural degradation of an insertion oxide associated with Li chemical extraction. Using a multi-technique approach that includes synchrotron radiation X-ray diffraction, scanning electron microscopy, micro Raman spectroscopy, photoelectron spectroscopy and conductive atomic force microscopy we reveal the balance between selective Li extraction and structural damage. We identify three different delithiation regimes, related to surface processes, bulk delithiation and damage generation. We find that only a fraction of the grains is affected by the delithiation process, which may create local inhomogeneities. However, the bulk delithiation regime is effective to delithiate the LCO film. All experimental evidence collected indicates that the delithiation process in this regime mimics the behavior of LCO upon electrochemical delithiation. We discard the formation of Co oxalate during the chemical extraction process. In conclusion, the chemical route to Li extraction provides additional opportunities to investigate delithiation while avoiding the complications associated with electrolyte breakdown and simplifying in-situ measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Drying of Spent Nuclear Fuel: Considerations and Examples

A recently revised American Society for Testing and Materials consensus standard guide for drying of spent nuclear fuel (SNF) provides considerations and guidance for preparing SNF for its safe storage in a sealed dry storage system. The standard discusses (1) needs for drying, (2) techniques to dry, and (3) demonstration of adequate dryness. No specific approach is prescribed since the effective techniques and needs for drying depend on the specifics of the fuel and dry storage system. Here, this paper discusses these topics using examples for both Zr-alloy-clad commercial SNF and for aluminum-alloy-clad research reactor SNF. Residual water can include free water (liquid and/or vapor), physisorbed water bound to internal surfaces, and chemisorbed water incorporated into surface films, such as (oxy)hydroxides. The potential impacts of these residual waters are corrosion/oxidation, radiolytic breakdown into gaseous and/or reactive species, and canister pressurization. For commercial SNF, inadvertent free water, even up to large amounts (e.g., 10+ mol), is not predicted to cause adverse corrosion degradation, except possible fuel oxidation for breached SNF. For aluminum-clad SNF, the production of radiolytic hydrogen with contribution from the chemisorbed water in its hydrated oxides is a primary consideration. For both SNF systems, canister pressurization is predicted to be well within the canister design, and flammability would not pose a safety concern using an oxygen limit of 5 vol % criterion. (Flammability control can be achieved by limiting either hydrogen or oxygen, and an oxygen limit is expected to be easier to meet in the presence of radiolytic H 2 generation.) The two primary technologies for SNF drying, vacuum drying and forced-gas dehydration, are described herein, and drying tests and campaigns using these methods are cited. Dryness criteria and the methods used to detect and measure residual (free) water are also discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Formation of Ba 3 Nb 0.75 Mn 2.25 O 9 -6H during thermochemical reduction of Ba 4 NbMn 3 O 12 -12R

The resurgence of interest in hydrogen-related technologies has stimulated new studies aimed at advancing lesser-developed water-splitting processes, such as solar thermochemical hydrogen production (STCH). Progress in STCH has been largely hindered by a lack of new materials able to efficiently split water at a rate comparable to ceria under identical experimental conditions. BaCe 0.25 Mn 0.75 O 3 (BCM) recently demonstrated enhanced hydrogen production over ceria and has the potential to further our understanding of two-step thermochemical cycles. A significant feature of the 12R hexagonal perovskite structure of BCM is the tendency to, in part, form a 6H polytype at high temperatures and reducing environments ( i.e. , during the first step of the thermochemical cycle), which may serve to mitigate degradation of the complex oxide. An analogous compound, namely BaNb 0.25 Mn 0.75 O 3 (BNM) with a 12R structure was synthesized and displays nearly complete conversion to the 6H structure under identical reaction conditions as BCM. The structure of the BNM-6H polytype was determined from Rietveld refinement of synchrotron powder X-ray diffraction data and is presented within the context of the previously established BCM-6H structure.

08 HYDROGEN↗
DOE OSTI2020

Polymer Retention Evaluation in a Heavy Oil Sand for a Polymer Flooding Application on Alaska’s North Slope

For a polymer flooding field trial in a heavy oil reservoir on Alaska’s North Slope, polymer retention is a key parameter. Because of the economic impact of retention, this parameter was extensively studied using field core material and conditions. Several important findings were noted. Polymer retention based on effluent viscosity measurements can be overestimated unless the correct (non-linear) relation between polymer concentration and viscosity is used. Polymer degradation (either mechanical or oxidative) can also lead viscosity-based measurements to overestimate retention. Inaccessible pore volume (IAPV) can be overestimated if insufficient brine is flushed through the sand between polymer banks. Around 100 pore volumes (PV) of brine may be needed to displace mobile polymer to approach a true residual resistance factor and properly measure IAPV. Even for a sand pack with kwsor = 20 mD, IAPV was zero for HPAM with molecular weight (Mw) of 18 million g/mol. Fine-grain particles (<20 μm) strongly impacted polymer retention values. Native NB#1 sand with a significant component of particles <20 μm exhibited 290 μg/g, while the same sand exhibited 28 μg/g after these small particles were removed. Polymer retention did not necessarily correlate with mineral composition. The NB#1, NB#3, and OA sands had similar elemental and clay compositions, but the NB#1 sand exhibited ~10 times higher retention than the NB#3 sand. Polymer retention did not necessarily correlate with permeability. NB#1 sand exhibited much higher retention than OA sand, even though NB#1 sand was twice as permeable as OA sand. No evidence of chromatographic separation of HPAM molecular weights was found in our experiments. Although retention tended to be greater without a residual oil saturation (than at Sor), the effect was not strong. Aging a core (with high oil saturation) at 60°C reduced HPAM retention by a factor of two. As expected, under similar conditions, polymer retention was greater for a higher Mw HPAM (18 million g/mol) than for a lower Mw HPAM (10-12 million g/mol). In many cases with high polymer retention values (e.g., 240 μg/g), polymer arrival at the end of the core was relatively quick, but achieving the injected concentration occurred gradually over many pore volumes. This effect was not due chromatographic separation of polymer molecular weights. Results from modeling of this behavior was consistent with concentrationdependent polymer retention. The form assumed for the retention function in a simulator can have an important impact on the timing and magnitude of the oil response from a polymer flood. Field-based observations can underestimate polymer retention, depending on when the tracer and polymer concentrations were measured and the assumptions made about reservoir heterogeneity.

Wang, Dongmei↗
DOE OSTI2024

Reliability of Materials and Components for Solid Oxide Fuel Cells

Planar stack solid-oxide fuel cells (SOFCs) require seals that must operate reliably under demanding conditions for lifetimes of 40000 hours. This includes temperature fluctuations between 800°C and RT during on and off cycles, thermal stresses, oxidizing environments and chemical degradation to name a few. This comprehensive report provides results from long term testing of two commercially available multicomponent barium alkali silicate glasses: SCN and G6, chosen as sealing candidates. In this scope, the glass seals were deposited on YSZ and Al 2 O 3 substrates simulating electrolytes (Zrbased) and coatings (both zirconia and Al 2 O 3 ). The seal-substrate couples were subjected to 800°C under air and steam+H 2 +N 2 environments up to 40000 hours to test their integrity under real operating conditions. Extensive studies on the effects of exposure have been conducted over the span of testing at various time intervals. Within the context of characterization, mechanical properties such as density, roughness, thermal expansion and glass transition, viscosity and wettability behavior; and microstructural properties such as glass chemistries, defect formation (cracks and pores), phase transformations (devitrification) and glass-interface reactions are investigated. Results and discussions are provided with a focus on the degradation of the properties over long term interrupted testing.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Designing SOC electrodes for better lifetime performance

Presentation for talk at the 2024 Pacific Rim Meeting of the Electrochemical Society October 6-11, 2024. The talk covers a review of NETL's solid oxide cell (SOC) performance degradation modeling framework and present case studies on how simulations are used to design better SOC electrodes.

Abernathy, Harry↗
DOE OSTI2024

Multi-Period Optimization of Multi-Timescale Energy Systems: Application to Solid-Oxide Electrolysis Cells

A presentation detailing the recent progress in the optimization of Solid-Oxide Cells under Chemical Degradation. The existing methods typically involve a quasi-steady state assumption to make this large-scale problem tractable. Here, we introduce an extension to this method that allows for adaptive coupling of degradation with the fast-timescale process based on a variety of error thresholds. This reduces the error accumulated during long-term optimization of the SOC under degradation and allows for decision making at multiple timescales. The results presented include long-term operating profiles of the SOC under degradation with both steady-state and fluctuating day to day operation.

Giridhar, Nishant↗
NASA NTRS1975

Combustion problems of nitramine propellants

This study has, as its distinctive feature, a detailed examination of the condensed-phase processes in the combustion of nitramine propellants. As a consequence of a recently developed model for the combustion of ammonium perchlorate (AP)/composite propellants, it is hypothesized that the condensed-phase degradation of the nitramine oxidizer particles to a vaporizable state is the overall rate-limiting step. It is also assumed that the gas-phase details are secondary in importance and need be studied only to the extent of supplying the correct boundary conditions on the condensed-phase/vapor-phase heat transfer. Because of imprecise understanding of the gas-phase processes in the presence of combustion, several plausible models are considered for the gas phase. It is found that all of the gas-phase models considered lead to predictions sufficiently close to experimental trends to conclude that the precise details of gas-phase processes are not of critical importance in determining propellant combustion behavior.

Kumar, R. N.↗
NASA NTRS1988

Chemical durability of high-temperature superconductor YBa2Cu3O(7-x) in aqueous environments

The stability of YBa2Cu3O(7-x) in water and 100-percent humidity has been investigated at three temperatures, using pH measurements, X-ray diffraction, and scanning electron microscopy. The oxide-ceramic superconductor is highly unstable; it reacts rapidly with water and degrades in moisture. Dissolution of the oxide perovskite in water is highly incongruent. The corrosion products are found to be BaCO3, CuO, O2, etc. Barium hydroxide is first formed and further reacts with atmospheric CO2 to form needle-shaped crystals of BaCO3. For any practical applications, devices made from these materials would have to be protected with an impermeable coating to prevent deterioration from atmosphere.

Bansal, Narottam P.↗
NASA NTRS1990

Optical surface refurbishment in space environment

The potential use of the vacuum environment of space to clean contaminated mirror surfaces or generate Al mirror surfaces with high reflectance in the 80-200-nm region is discussed and illustrated with diagrams and graphs, reviewing previous studies and current experiment proposals. Consideration is given to (1) applying the atomic oxygen plasma environment of LEO to clean coated mirrors and (2) depositing freshly evaporated Al onto a mirror surface in vacuum, providing relatively long periods of high EUV reflectance before oxidation of the surface degrades performance: such a procedure could be performed as a maintenance measure or even incorporated into the design of a space observatory. A free-flying experiment is described which would produce and maintain an Al surface with controlled exposure to OH, H2O, and O2; demonstrate directed-beam Al deposition onto a simulated telescope/spectrometer surface; monitor instrument reflectance/sensitivity over time; and demonstrate in situ refurbishment of the degraded surface.

Heaney, James B.↗