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At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Quaternary i-MAX Phases (Mo 2/3 RE 1/3 ) 2 AlC (RE: Dy, Tb, Er): Experimental Characterization and First-Principles Insights into their Fundamental Properties

Rare earth (RE)-based materials have unique electronic, magnetic, and optical properties, leading to the recent discovery of atomically layered solids with the chemical formula (M' 2/3 RE 1/3 ) 2 AlC, which have since garnered significant attention in the scientific community. This study aims to synthesize, characterize, and investigate the structural and thermal stability of the RE i-MAX phases. We prepared i-MAX phases using molybdenum (Mo) as M′ and RE elements as Dy, Tb, and Er, namely (Mo 2/3 Dy 1/3 ) 2 AlC, (Mo 2/3 Tb 1/3 ) 2 AlC, and (Mo 2/3 Er 1/3 ) 2 AlC. Structural characterization through x-ray diffraction (XRD) and Raman spectroscopy confirms the formation of the RE-based i-MAX phase, along with the presence of minor impurity phases in the alloys. Thermogravimetric analysis (TGA) conducted up to 1000°C under ambient conditions reveals that the i-MAX phases remain thermally stable up to approximately 450°C, beyond which oxidation leads to a noticeable weight gain in all samples. Differential scanning calorimetry (DSC) measurements during heating and cooling cycles show endothermic and exothermic peaks for (Mo 2/3 Dy 1/3 ) 2 AlC i-MAX in the 410–420°C range, indicating a temperature-induced minor atomic arrangement. In contrast, these peaks are absent in the Tb- and Er-based i-MAX phases. These findings offer valuable insights into the thermal behavior and stability of these i-MAX phases under thermal stress, contributing to a deeper understanding of their unique properties. Furthermore, first-principles density functional theory (DFT) calculations were performed to investigate the electronic and optical properties of the i-MAX phases. The results reveal their metallic nature, with pronounced contributions from Mo and RE elements near the Fermi level and within the conduction band.

Rare earth↗
DOE OSTI2021

Stress- and Time-Dependent Formation of Self-Lubricating In Situ Carbon (SLIC) Films on Catalytically-Active Noble Alloys

Abstract Low shear strength (30 MPa) organic films were grown in situ on Pt 0.9 Au 0.1 surfaces via cyclic sliding contact in dry N 2 with trace concentrations of ambient hydrocarbons. We present a systematic investigation of the stress- and time-dependent film formation. Steady-state friction coefficients were found to be as low as µ ~ 0.015 and inversely proportional to contact pressure, revealing non-Amontonian behavior. Above a Hertzian contact pressure of ~500 MPa, shear strength dropped, indicating an activated process. Raman spectroscopy identified non-uniformity in areal coverage and relative order with contact pressure. Regions of steady-state low-friction behavior exhibited spectra similar to DLC coatings. Atomic force microscopy was used to study the formation and growth of films at the nanoscale. Stress- and time-dependent measurements suggested a sublinear increase of film volume with time, and a transition from growth to wear at a Hertzian contact pressure of ~1.2 GPa.

Jones, Morgan R.↗
DOE OSTI2021

Wafer-scale quasi-layered tungstate-doped polypyrrole film with high volumetric capacitance

Layered materials are particularly attractive for supercapacitors because of their unique physical, electrical and chemical properties. In this work, we demonstrate a facile and scalable electrochemical deposition method for wafer-scale synthesis of quasi-layered tungstate-doped polypyrrole films (named TALPy) with controllable thickness and size. The as-prepared TALPy film exhibits a high gravimetric density and excellent volumetric capacitance, exceeding many high-performing carbon- and polymer-based film electrodes. Based on combined results of ex-situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS), it is determined that TALPy stores charge through an ion intercalation process accompanied by change in oxidation states of polypyrrole backbone, which is referred as intercalation pseudocapacitance. All these results suggest the great promise of electrochemical deposition as a scalable and controllable bottom-up approach for synthesizing quasi-layered conductive organic-inorganic hybrid films for electrochemical energy storage applications with high volumetric performance.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Paper or Plastic? Multiscale Material Handling Properties of Two Model Municipal Solid Waste Streams

Purpose: Municipal Solid Waste (MSW) is a potentially valuable sustainable feedstock for fuel and chemical production due to its carbon-rich content and low cost. This study aims to assess the material handling properties of paperand plastic-rich MSW feedstocks to mitigate equipment failure and processing downtime. Methods: The material handling properties of crumbled MSW feedstocks were measured using apowder rheometer with mass flow hopper calculations to assess handling performance. Inverse gas chromatography was use to measure the surface energy differences between feedstocks. Electron microscopy and Raman spectroscopy was used to evaluate microscale features that may contribute to material handling differences. Results: Plastic and paper rich feedstocks crumbled to a nominal 2 mm particle size were observed to have similar flow and handling characteristics with reasonable hopper outlets. 2 mm plastic rich crumbles, with their higher bulk density, exhibited superior flow performance. By contrast, 4 mm material required significantly larger hopper outlets, indicating poor flowability. Paper rich and 4 mm plastic rich samples displayed broad particle size distributions, which contributed to particle interlocking, jamming, and other flow issues. Electron microscopy revealed that plastic rich samples were significantly smoother, enhancing their flowability compared to the rougher, paper rich materials. Conclusions: This study establishes critical material handling baselines for processing MSW as a viable feedstock for fuel and chemical production. The findings highlight the importance of optimizing particle size and feedstock composition to improve flowability and handling performance.

09 BIOMASS FUELS↗
DOE OSTI2022

Direct Fabrication of Vertically Stacked Double Barrier Tunnel Junctions Based on Graphene and h-BN

Direct manufacturing of two-dimensional material-based double barrier (DB) tunnel junctions, based on a lithography-free approach was developed. Graphene/h-BN/Graphene/h-BN/Graphene devices were deposited on Si/SiO2 substrates by employing a plasma enhanced chemical vapor deposition technique in a sequential manner. DB tunneling junctions with varying barrier widths (by varying the thickness of the second graphene layer) were studied. Samples were characterized using Raman, Atomic Force Microscopy and X-ray photoemission spectroscopy. The I–V characteristics of tunneling current showed resonant tunneling behavior at room temperature with a negative differential conductance. The behavior could be explained with quantum mechanical double barrier tunneling model in which analytic solutions to Schrödinger’s equation were obtained in each region of the system. Resonances in transmission probability coefficient for varying barrier widths were evaluated and compared with the experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tunable phase structure in NaNbO 3 ceramics by grain-size effect, electric field and heat treatment

Large polarization and strain change during antiferroelectric - ferroelectric phase transition under electric field is the foundation for realizing excellent electrical properties in antiferroelectric ceramics, therefore, the adjustment of antiferroelectricity and clarification of the corresponding mechanism is the foundation for controlling electrical properties. NaNbO3 is the most complex perovskite system showing multiple antiferroelectric phases in a wide temperature range, in which the antiferroelectricity shows obvious instability with changing external and internal conditions, namely the antiferroelectric phase can be adjusted by grain-size effect, electric field and heat treatment. According to the systematical study in terms of the Rietveld refinement of synchrotron XRD and Raman, NaNbO3 exhibits a ferrielectric P21ma structure at room temperature, the ferroelectric component of which increases with decreasing grain size. Two antiferroelectric tetragonal phases exist around Curie temperature TC before the entrance of antiferroelectric R phase zone, while an antiferroelectric monoclinic phase, which can be maintained to room temperature by annealing treatment, acts as the bridge for the depolarization of the poled NaNbO3 with ferroelectric Q phase. A detailed phase diagram mainly focused on the antiferroelectric phase zones of NaNbO3 is plotted, which gives a clear understanding about the polymorphic phase transitions under different conditions. Finally, the results concluded in this work would give a clear guidance for designing high-performance NaNbO3-based lead-free ceramics from the point of structure.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Comprehensive characterization of the irradiation effects of glassy carbon

Carbon materials have become increasingly diverse, finding applications in high-temperature and high-radiation environments. Glassy carbon, an allotrope known for its exceptional chemical inertness and desirable mechanical properties. However, understanding neutron irradiation effects in glassy carbon has proven challenging, primarily because of its unique nanopore structure. Here, this study presents a highly detailed microstructural characterization investigation of neutron-induced changes in glassy carbon, revealing how changes in nanopore structure and crystallinity impact the irradiation-induced shrinkage. Aberration-corrected scanning transmission electron microscopy (STEM) reveals pore closure that leads to material densification in the irradiated samples. Dimensional analysis combined with comparison to historical data suggest significant length shrinkage to occur. Neutron and in situ electron irradiation experiments suggest that glassy carbon transforms into so-called carbon onions, supporting the concept of shrinkage saturation. Investigating irradiation temperature effects using STEM, electron energy loss spectroscopy, x-ray diffraction, and Raman spectroscopy revealed partial amorphization at 210 °C–230 °C and preserved order in glassy carbon at 860 °C, coinciding with pore closure. Thermal property measurements were also conducted to assess the effects of densification and other changes in the atomic structure of glassy carbon. The results of this study have broad implications in the deployment of glassy carbon to nuclear environments, based around the observed changes in the thermal properties, and demonstrates the operational window for the onset of densification.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Hierarchical domain structures in buckled ferroelectric free sheets

Flat elastic sheets tend to display wrinkles and folds. From pieces of clothing down to two-dimensional crystals, these corrugations appear in response to strain generated by sheet compression or stretching, thermal or mechanical mismatch with other elastic layers, or surface tension. Extensively studied in metals, polymers and, — more recently — in van der Waals exfoliated layers, with the advent of thin single crystal freestanding films of complex oxides, researchers are now paying attention to novel microstructural effects induced by bending ferroelectric-ferroelastics, where polarization is strongly coupled to lattice deformation. Here we show that wrinkle undulations in BaTiO3 sheets bonded to a viscoelastic substrate transform into a buckle delamination geometry when transferred onto a rigid substrate. Using spatially resolved techniques at different scales (Raman, scanning probe and electron microscopy), we show how these delaminations in the free BaTiO3 sheets display a self-organization of ferroelastic domains along the buckle profile that strongly differs from the more studied sinusoidal wrinkle geometry. Moreover, we disclose the hierarchical distribution of a secondary set of domains induced by the misalignment of these folding structures from the preferred in-plane crystallographic orientations. Our results disclose the relevance of the morphology and orientation of buckling instabilities in ferroelectric free sheets, for the stabilization of different domain structures, pointing to new routes for domain engineering of ferroelectrics in flexible oxide sheets.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of thermal treatment on structure and catalytic performance of ceria-zirconia supported copper oxide (CuO x /Ce y Zr 1-y O 2 ) catalysts for CO oxidation

Copper oxide (CuO x ) supported on ceria-zirconia (Ce y Zr 1-y O 2 , y = 1.0, 0.5, 0.0) catalysts were investigated to elucidate the effects of thermal treatment on their physicochemical properties and catalytic performance in carbon monoxide (CO) oxidation. Here, the catalysts were synthesized via a one-pot chemical vapor deposition (OP-CVD) method at 700˚C and 900˚C with controlled Cu loading. Characterization techniques, including synchrotron X-ray diffraction (S-XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma spectroscopy (ICP), and N 2 adsorption-desorption, were implemented to probe the crystalline structure, molecular and electronic structure, oxygen vacancies, specific surface area (SSA) and metal loading. CO oxidation was chosen as a model reaction to explore the structure-catalytic performance relationship. A ∼100% CO conversion was achieved at < 150˚C, particularly with the CuO x /CeO 2 catalyst calcined at 700˚C. In contrast, calcination at 900˚C caused a ∼90% decrease in SSA and a ∼24% increase in T 50 . Activity tests revealed that increasing ZrO 2 content lowered CO oxidation activity despite generating more defect sites. In-situ measurement of the 700 °C calcined samples revealed the presence of stable and unstable defects in CuO x /Ce 0.5 Zr 0.5 O 2 and CeO 2 respectively, which play a key role in the activity of the catalysts. The results highlight that catalytic performance is closely related to the SSA. Furthermore, an optimum calcination temperature favor significant oxygen vacancy formation with required CuO x -support interactions, enhancing redox properties and catalytic performance.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Probing the surface of promoted CuO-Cr 2 O 3 -Fe 2 O 3 catalysts during CO 2 activation

The influence of basic oxide promoters on copper-chromium-iron oxide catalysts was investigated to determine the nature of surface oxygen species and structure-activity relationship for the reverse water-gas shift reaction. The catalysts were characterized with in situ XRD, in situ Raman, in situ XPS, in situ HS-LEIS and H 2 -TPR. Two surface oxygen sites with different reduction characteristics were found to be present. The overall CO 2 activation rate was found to correlate with both the number and reducibility of the more active oxygen species that were likely associated with the Cu-FeO x interfacial regions for enhanced hydrogen spillover. While addition of K 2 O somewhat preserved the interfacial regions and facilitated the reduction kinetics of surface oxygen, both Na 2 O and CaO significantly suppressed the availability of metallic Cu as well as the Cu-FeO x interfaces, leading to decreased reactivity. These findings provide a direction to promote the copper-iron catalysts by creating more metal-metal oxide interfacial sites.

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

Partial oxidation of isobutylene using Ni TiO x

In this work, we report an aerobic partical oxidation of isobutylene into isoprene, acetone, and p-xylene using a mesoporous Ni TiO x catalytic material. In this work, two catalysts were found to synthesize two of these three valuable products with high selectivity, with p-xylene being synthesized with a selectivity of 46.0% and isoprene being synthesized with a selectivity of 64.7%, with overall conversions of isobutylene being 34.0% and 11.9% respectively. These reactions were done at relatively low temperatures. (300°C or below) and are conducted at flow rates of 10 sccm oxygen and isobutylene. The nickel titania catalysts were studied extensively using various characterization methodologies such as TEM, Raman, XRD, and XRF.

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

Precisely doping the surface of tin-based electrocatalysts for improved CO 2 conversion to liquid chemicals

Doping tin catalysts with sulfur can improve the electrochemical CO 2 conversion into formate/formic acid, but the lack of composition-dependent activity trends hinders further catalyst development. Here, we precisely controlled the composition of sulfur-doped Sn catalysts to show that sulfur doping only improves CO 2 conversion over a very narrow composition range, achieving maximum activity at 1.4 at% S. In situ Raman spectroscopy indicted working catalysts were in a primarily metallic state (e.g. S-Sn), and we achieved some of the highest reported partial current densities in both H-cell and full-cell electrolyzer configurations. Density Functional Theory calculations predicted S atoms preferentially occupied the catalyst surface and improved CO 2 reduction by localizing charge density at the catalyst/intermediate interface, which stabilized the *OCOH intermediate and lowered the CO 2 conversion thermodynamic barrier. Our work quantifies the composition-dependent influence of S dopants on Sn-based CO 2 reduction catalysts and provides a pathway for maximizing their CO 2 conversion activity.

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

A highly oxygen reduction reaction active and CO 2 durable high-entropy cathode for solid oxide fuel cells

One big obstacle for the oxygen reduction reaction (ORR) electrode in solid oxide fuel cells (SOFCs) is the poor reaction activity and fast degradations caused by CO 2 poisoning. Here, in this study, we report our design of an active A-site Ca-rich high-entropy Pr 0.1875 Ba 0.1875 Sr 0.1875 La 0.1875 Ca 0.25 CoO 3-δ (PBSLC 25 C) electrode, guided by the O p-band theory. Here, when applied as a cathode in solid oxide fuel cells (SOFCs), it demonstrates high ORR activity and excellent CO 2 tolerance under realistic operating conditions. Ni-YSZ-based anode-supported cells with PBSLC 25 C cathodes demonstrate excellent peak power densities of 1.14 W cm -2 , 1.04 W cm -2 , and 0.77 W cm -2 in the air with 1%, 5%, and 10% CO 2 , respectively, at 750 °C. The engineered high-entropy PBSLC 25 C effectively diminishes the CO 2 poisoning effect and maintains active surfaces for fast oxygen exchange, as confirmed by the cell durability test in air containing CO 2 (5 and 10 vol%), Raman spectroscopy, and density functional theory calculations.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Understanding the Origin of Negative Temperature Dependence and Activity of N-Coordinated Cobalt Sites During Ethylene Dimerization

The on-demand production of short-chain linear alpha olefins (LAOs; C4-C8) via C2H4 dimerization and oligomerization is industrially attractive, prompting extensive research on designing active, selective, and stable catalysts for industrial use. Cobalt supported on ammoniated carbon (Co(NH3)x/C) catalysts have shown remarkable activity and selectivity in this process. However, critical aspects such as the active phase, active site structure, the role of the catalyst support, cobalt loading effects, and the inverse correlation of the reaction rate with temperature remain inadequately understood. This study systematically explores these factors using a combination of steady-state differential catalytic tests, in situ molecular characterization including diffuse reflectance UV-Vis (DR-UV-Vis), Infrared, and Raman spectroscopies, and ex situ X-ray diffraction (XRD) and high annular aberration-corrected dark field transmission electron microscopy (HAADF-STEM). Various supports (SiO2, Al2O3, NH4-ZSM-5, g-C3N4, and C) and cobalt loadings (1.0-3.0 Co nm-2) were studied to determine the optimal catalyst composition and identify the active phase and sites. Carbon-supported catalysts uniquely produce C4-8 LAOs during C2H4 dimerization, with site-time-yield remaining constant (~10-3 s-1) for 1.0-4.0 Co nm-2 at prolonged reaction times (24-48?h time-on-stream). At higher loadings of 6.0 Co nm-2, the formation of crystalline CoO and Co3O4 phases reduces catalytic activity and LAO selectivity. Our findings show that active catalysts lack crystalline cobalt oxides and instead feature dispersed Co2+ sites, tetra-coordinated to a mix of N/NH3 and O/H2O ligands, which catalyze C2H4 dimerization via the Cossee-Arlman mechanism, exhibiting 1st order dependence on C2H4 concentration. The observed inverse rate-temperature correlation is attributed to compensation effects (i.e., presence of Cremer-Constable relationship) linked to changes in adsorption enthalpic and entropic factors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Heterostructured nano-catalysts with efficient metal-oxide interfaces unlock high-performance direct methanol protonic ceramic fuel cells

Direct methanol protonic ceramic fuel cells (PCFCs) are attractive due to their low cost, convenient storage, and high volumetric energy density, as well as their suitability for transportation. However, the poor coking tolerance of conventional nickel-based anodes leads to their susceptibility to severe carbon deposition and significant deactivation after long-term exposure to hydrocarbons. Herein, we report a nano-catalyst of Ce 0.6 Ni 0.2 Cu 0.2 O 2 with a heterogeneous structure that is spontaneously reduced into a Ce 0.6 Ni 0.2-x Cu 0.2-x O 2-δ (CeNCO) oxide framework interfaced with a nano NiCu alloy (denoted as NC/CeNCO) under operating conditions, as confirmed by analyses of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. A Ni-BaCe 0.7 Y 0.06 Yb 0.06 Zr 0.06 Hf 0.06 Gd 0.06 O 3-δ anode-supported PCFC employing the NC/CeNCO metal-oxide catalyst achieved a peak power density of 1.11 W cm −2 and operational stability of about 100 h at 700 °C when fueled by 35 % CH 3 OH-15 % H 2 O-50 % N 2 . In conclusion, the enhanced performance and coking resistance are attributed to the efficient interfaces of Ni, Cu, and ceria-based oxide in NC/CeNCO for CH 3 OH reforming, as confirmed by analyses of electrochemical performance and Raman spectroscopy with density functional theory calculations, revealing that these interfaces can enhance CH 3 OH activation and promote efficient OH-mediated carbon removal via COH intermediates.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Systematic investigations on iron cycling in phosphorus/siderophore systems: Synergism or antagonism?

Synergisms between microbial exudates on Fe (hydr)oxide dissolution as an effective Fe acquisition pathway have been recently addressed and vigorously debated. However, Fe liberation mechanisms and where siderophores and phosphorus (P) coexist received little attentions. Current study systematically investigated ferrihydrite dissolution in the presence of desferrioxamine B (DFOB) (a kind of fungally-derived siderophores) and inorganic/organic phosphorus (orthophosphate, Pi; myo-inositol hexaphosphate, IHP), as a function of solute pH, reaction time and reagent content. Reacted solids were characterized by N 2 -BET adsorption, zeta (ζ) potential analysis, sequential extraction analysis (SEDEX), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), micro Raman spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Our results indicate that upon reaction with P-only or (DFOB + P) systems, interfacial complexation partially switched from monolayer bidentate-binuclear surface complexes to ternary complexes, or laterally transformed into amorphous Fe–P precipitates. The Fe-Pi complex precipitated more readily under acidic conditions, and Fe-IHP complex preferentially nucleated in neutral-alkaline environments. Phosphorus slightly promoted Fe release from minerals and fixation to the leached layer or interfacial liquid zone initially, but subsequently prevented further attacks from protons and DFOB. The co-effects of P and DFOB likely correspond to two successive scenarios: 1) DFOB is preferentially attracted toward ferrihydrite surfaces by negative electrical fields induced by adsorbed phosphorus and can act synergistically with labile P–Fe complexes, resulting in intensive temporal dissolution of Fh; 2) subsequent Fe shuttling to DFOB can be prohibited by stabilized, passive P/Fe–P layers. Finally, our results emphasize the antagonism between P compounds and siderophores (i.e., DFOB here) on ferrihydrite dissolution to improve understanding of the biologically-mediated Fe cycling in natural systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Generalized synthesis of high surface area mesoporous metal titanates as efficient heterogeneous catalysts

A novel metal dissolution coupled with reverse micelle formation approach is used as a generalized synthesis method for a series of high surface area metal titanates where the metals used are Bi, Mg, V, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, and Ce. This study reports the highest surface areas published so far. The homogeneous distributions of the metals and titanium are observed in SEM-EDX and TEM mapping. The synthesized materials were comprehensively characterized using PXRD, Raman, nitrogen adsorption isotherms, SEM; EDX, TEM, TEM mapping, TGA, and XPS. The green catalytic oxidation of aniline to nitrosobenzene occurs within 30 min at room temperature when mesoporous W/Ti binary metal oxide is used as the catalyst. The radical mediated catalytic reaction gives excellent yields and the catalyst is reusable up to 4 reaction cycles without losing significant activity.

36 MATERIALS SCIENCE↗