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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE

Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification. Aims. We aim to spatially resolve the photospheric extent as well as the circumstellar environment. Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3–4 μm), M (4.5–5 μm), and N (8–13 μm) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics simulations carried out with CO5BOLD and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes OPTIM3D and RADMC3D to compute the spectral energy distribution for the L, M, and N bands, respectively. Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N-band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration. Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of VX Sgr’s stellar surface and circumstellar environment across a very large spectral domain for the first time.

stars: atmospheres↗
DOE OSTI2025

Unveiling the Mechanism of Mn Dissolution Through a Dynamic Cathode‐Electrolyte Interphase on LiMn2O4

Abstract Understanding the formation and evolution of the cathode‐electrolyte interphase (CEI), which forms at the interface between the cathode and electrolyte, is crucial for revealing degradation mechanisms in cathode materials, especially for developing strategies to stabilize the interphase in the strongly oxidizing conditions that evolve at high operating voltages in next‐generation Li‐ion batteries. However, The present understanding of the CEI is challenged by its complex and dynamic nature. In this work, near‐edge X‐ray absorption fine structure spectroscopy, electrochemical characterization, and reactive molecular dynamics simulations are combined to reveal a mechanism for CEI formation and evolution above model LiMn 2 O 4 (LMO) thin‐film electrodes in contact with conventional carbonate‐based electrolytes. It is found that Mn dissolution from LMO can be understood in terms of repetitive Mn 3 O 4 formation and dissolution behavior during cycling, which is closely connected to electrolyte decomposition and a key aspect of the CEI formation and growth. The behavior of the CEI in this model system offers detailed insight into the dynamic chemistry of the interphase, underscoring the important role of electrolyte composition and cathode surface structure in interphase degradation.

Ou, Wenhan↗
DOE OSTI2017

Layer-by-Layer Molecular Assemblies for Dye-Sensitized Photoelectrosynthesis Cells Prepared by Atomic Layer Deposition

In a Dye Sensitized Photoelectrosynthesis Cell (DSPEC) the relative orientation of catalyst and chromophore play important roles. Here we introduce a new, robust, Atomic Layer Deposition (ALD) procedure for the preparation of assemblies on wide bandgap semiconductors. In the procedure, phosphonated metal complex precursors react with metal ion bridging to an external chromophore or catalyst to give assemblies bridged by Al(III), Sn(IV), Ti(IV), or Zr(IV) metal oxide units as bridges. The procedure has been extended to chromophore-catalyst assemblies for water oxidation catalysis. A SnO2 bridged assembly on SnO2/TiO2 core/shell electrodes undergoes water splitting with an incident photon conversion efficiency (IPCE) of 17.1% at 440 nm. Reduction of water at a Ni(II)-based catalyst on NiO films has been shown to give H2. Compared to conventional solution-based procedures, the ALD approach offers significant advantages in scope and flexibility for the preparation of stable surface structures.

DSPEC, core/shell, Atomic Layer Deposition, self-a↗
DOE OSTI2017

Core–Shell Nanostructured Cobalt–Platinum Electrocatalysts with Enhanced Durability

Pt-bimetallic alloys involving 3d transition metals (Co, Ni, etc.) are promising electrocatalysts for the oxygen reduction reaction (ORR). Despite the enhanced catalytic activity versus Pt, the electrocatalytic performance of Pt-bimetallic catalysts is however limited by the lack of long-term durability, primarily due to the leaching of the non-noble element under harsh electrochemical conditions. In this work, our study shows that the core–shell nanostructure comprising a Pt shell and a cobalt core (denoted as Co@Pt) could overcome this limitation, demonstrating ~10 times improvement in catalytic activity versus commercial Pt catalysts and no more than 13% of loss after 30000 potential cycles. The evolutions of nanoscale and surface structures over the course of extensive potential cycling were followed by combining electron microscopic elemental mapping and electrochemical studies of CO stripping. Atomistic simulations and density functional theory calculations suggest that the core–shell nanostructure could protect the non-noble cobalt from leaching under the “electrochemical annealing” conditions while maintaining the beneficial mechanisms of bimetallic systems for catalytic activity enhancement.

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

CO2 Hydrogenation to Hydrocarbons over Fe/BZY Catalysts

This manuscript reports a CO2 hydrogenation process in a catalytic laboratory-scale packed-bed reactor using an Fe/BZY15 (BaZr0.8Y0.15O3-d) catalyst to form hydrocarbons (e.g., CH4, C2+) at elevated pressure of 30 bar and temperatures in the range 270 = T = 375 degrees C. The effects of temperature, feed composition (i.e., CO2/H2 ratio, and residence time (i.e., Weight Hourly Space Velocity (WHSV) are studied to understand the relationship between CO2 conversion and carbon selectivity. Catalyst characterization elucidates the relationships between the catalyst structure, surface adsorbates, and reaction pathways. Thermodynamic analyses guide the experimental conditions and assist interpreting results. While the feed composition and temperature influence the product distribution, the results suggest that the higher-carbon (C2+) selectivity and yield depend strongly on residence time. The results suggest that the CO2 hydrogenation reaction pathway is similar to Fischer-Tropsch (FT) synthesis. The reaction begins with CO2 activation to form CO, followed by chain-growth reactions similar to the FT process. The CO2 activation depends on the redox activity of the catalyst. However, the carbon chain growth depends primarily on the residence time. as is the case for the FT synthesis, high residence time (on the orders of hours) is required to achieve high C2+ yield. For such high residence times, catalyst-fouling carbon deposition can be problematic. The coke-resistant BZY15 catalyst support contributes to the catalytic activity and enables a coke-free operation for more than 100 h time-on-stream.

bi-functional catalyst↗
DOE OSTI2019

Evolution of photoresist layer structure and surface morphology under fluorocarbon‐based plasma exposure

Abstract Ion bombardment of photoresist materials during plasma etching results in the formation of a surface dense amorphous carbon (DAC) layer that contributes to both etch resistance and the development of surface roughness. Real‐time ellipsometric measurements/analysis reveals that a C 4 F 8 ‐containing plasma interacts with an Ar‐plasma‐formed DAC layer to produce a modified DAC/fluorocarbon (FC) layer by FC deposition/diffusion of fluorine into the surface. The depletion of the DAC layer via modification and ion bombardment causes the etch rate of the bulk layer to increase. As the modified surface layer is formed, a noticeable decrease in surface roughness decrease is observed. These findings provide an understanding of the mechanisms of atomic layer etching processes in photoresist materials.

Pranda, Adam↗
DOE OSTI2018

Synthesis, Crystal Structure, Hirshfeld Surface Analysis, and Physicochemical Study of an Anhydrous Organic Acidic Cyclohexaphosphate

The new organic–inorganic hybrid [5-Cl-2-(CH{sub 3})C{sub 6}H{sub 3}NH{sub 3}]{sub 4}H{sub 2}P{sub 6}O{sub 18} has been synthesized by the slow evaporation method. X-ray diffraction on a single crystal shows that this acidic cyclohexaphosphate crystallized in the monoclinic space group C{sub 2/c} with a = 33.89(11) Å, b = 9.16(16) Å, c = 13.68(3) Å, β = 91.35(2)°, V = 4244.9(19) Å{sup 3} and Z = 4. {sup 31}P MAS-NMR and {sup 13}C CP/MAS-NMR results are in accordance with X-ray findings. Fluorescent study shows the blue photoluminescence. Furthermore, FT-IR analysis was studied and the complete vibrational assignments were done. Intermolecular interactions were analyzed using Hirshfeld surface analysis and the associated 2D fingerprint plots.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effect of ball milling conditions on microstructure and lithium storage properties of LiNi0.5Mn1.5O4 as cathode for lithium-ion batteries

Highlights: • Precursors of LNM respectively synthesized by dry and wet ball-milling. • Under wet ball-milling raw materials form slurry and mix well in microscale. • LNM-w12 sample presents proper stoichiometric composition and the highest D{sub Li}{sup +}. • At 0.1 C rate LNM-w12 delivers 133 mAh g{sup −1} at 100 cycle close to theoretical value. • LNM-w12 delivers 97 mAh g{sup −1} at 10 C rate and remains 78% after 1000 cycles. - Abstract: In this work, the precursors of LiMn{sub 1.5}Ni{sub 0.5}O{sub 4} (LNM) are respectively synthesized by dry and wet ball-milling. Under wet ball-milling, the problem of sticky residue in dry ball-milling is effectively resolved, the three raw materials form homogeneous slurry and mix well in micrometers level. LNM-w12 sample synthesized by using precursor added 12 mL milling medium gains the atomic composition closed to the theoretical value, ordered crystal structure and the highest lithium diffusion coefficient. At 0.1 C rate, LNM-w12 delivers the capacity of 136 mAh g{sup −1} at the first cycle, and 133 mAh g{sup −1} at the 100th cycle. Moreover, LNM-w12 delivers the initial capacity of 97 mAh g{sup −1} at 10 C rate, and remains 78% after 1000 cycles. The great rate capability of LNM-w12 can be attributed to the well-formed crystal structure, ordered and stable surface structure, which is conducive to the diffusion of lithium ions and prevents the dissolution of the material at high voltage.

25 ENERGY STORAGE↗
DOE OSTI2020

Raman Spectroscopy Analysis of the Structure and Surface Chemistry of Ti3C2Tx MXene

Raman spectroscopy is one of the most useful tools for the analysis of two-dimensional (2D) materials. While MXenes are a very large family of 2D transition metal carbides and nitrides, there have been just a few Raman studies of materials from this family. Here, we report on a systematic study of the most widely used and most important MXene to date: Ti 3 C 2 T x . By synthesizing material using different methods, we show that Raman spectra of Ti 3 C 2 T x are affected not only by the composition and surface groups but also by intercalated species and stacking. Due to a plasmonic peak of Ti 3 C 2 T x around 785 nm, resonant conditions are achieved, enabling us to observe an extra peak at ~120 cm –1 , when excited with a red diode laser. We report differences in Raman spectra collected from single flakes of Ti 3 C 2 T x , colloidal solutions, and multilayer films. Lastly, we show how an undesirable photoluminescent background could serve as evidence of material degradation, which leads to the formation of defective titania and amorphous carbon. Overall, this study shows how Raman spectroscopy can be used for the characterization of important emerging 2D materials: MXenes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗