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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

An Alternative Explanation for the Great Oxygenation Event (GOE): Weathering of Rocks Containing Minerals With Peroxy Bonds

During the Great Oxygenation Event (GOE) 2.42.35 Gyrsago, Earth experienced a notable shift in its oxidation state. This has been widely attributed to cyanobacteria having “invented” oxygenic photosynthesis. We present a very different view based on the fact thatoxygen is released from rocks during weathering. If so, the GOE must have been caused by an influx of abiogenicO2 into Earth’s surface environment. Minerals forming Earth’s crust contain impurity hydroxyls such as O3SiOH. Pairs of those are known to undergo a common redox conversion, ubiquitously forming peroxydefects plus H 2 : O 3 SiOH-HOSiO 3 ⇌O 3 Si/ OO \SiO 3 + H 2 Being diffusively mobile, most H 2 will be lost, leaving behind bound O as peroxy. The peroxy defects release O 2 during weathering: O 3 Si/ OO \SiO 3 + H 2 O → O 3 SiOH-HOSiO 3 + 1 ⁄ 2 O 2 We suggest that this abiogenically generated O 2 was responsible for the progressive oxidation of the early Earth and that this abiotic process drove the Great Oxygenation Event (GOE).

Great Oxygenation Event↗
NASA NTRS2023

The northernmost hyperspectral FLoX sensor dataset for monitoring of high-Arctic tundra vegetation phenology and Sun-Induced Fluorescence (SIF)

A hyperspectral field sensor (FloX) was installed in Adventdalen (Svalbard, Norway) in 2019 as part of the Svalbard Integrated Arctic Earth Observing System (SIOS) for monitoring vegetation phenology and Sun-Induced Chlorophyll Fluorescence (SIF) of high-Arctic tundra. This northernmost hyperspectral sensor is located within the footprint of a tower for long-term eddy covariance flux measurements and is an integral part of an automatic environmental monitoring system on Svalbard (AsMovEn), which is also a part of SIOS. One of the measurements that this hyperspectral instrument can capture is SIF, which serves as a proxy of gross primary production (GPP) and carbon flux rates. This paper presents an overview of the data collection and processing, and the 4-year (2019–2021) datasets in processed format are available at: https://thredds.met.no/thredds/catalog/arcticdata/infranor/NINA-FLOX/raw/catalog.html associated with https://doi.org/10.21343/ZDM7-JD72 under a CC-BY-4.0 license. Results obtained from the first three years in operation showed interannual variation in SIF and other spectral vegetation indices including MERIS Terrestrial Chlorophyll Index (MTCI), EVI and NDVI. Synergistic uses of the measurements from this northernmost hyperspectral FLoX sensor, in conjunction with other monitoring systems, will advance our understanding of how tundra vegetation responds to changing climate and the resulting implications on carbon and energy balance.

hyperspectral field sensor↗
NASA NTRS2025

Thermochemical Stability of Ca2Yb8(SiO4)6O2 Apatite in Presence of Molten Calcium-Magnesium-AluminoSilicate (CMAS)

Thermochemical stability of ytterbium silicon oxyapatite Ca 2 Yb 8 (SiO 4 ) 6 O 2 (CYbS) in the presence of molten calcium-magnesium aluminosilicate (CMAS) has been investigated at elevated temperatures. CYbS apatite powder was synthesized from the constituent oxides via solid state reaction method. Hot pressed apatite substrates were exposed to molten CMAS at 1200, 1300, and 1400 °C for 1, 10, and 50 h. Development of phases in the interaction region of the heat-treated specimens was monitored using scanning electron microscopy, transmission electron microscopy, high angle annular dark field imaging, selected area electron diffraction and energy dispersive X-ray spectroscopy. Monoclinic cyclosilicate Ca 3 Yb 2 (Si 3 O 9 ) 2 formed from interaction of CYbS apatite with CaO in the CMAS melt at the apatite-CMAS reaction front and continued to nucleate and grow within the residual CMAS in diffusion couples annealed for 1-50 h at 1200 °C and those heat treated at 1300 °C for 1 h. Residual CMAS was Ca-depleted when cyclosilicate was present. Dendritic wollastonite CaSiO 3 was observed within the residual CMAS in couples annealed at 1200 and 1300 °C. Ingress of molten CMAS, because of its exponential decrease in viscosity, occurred through open pores and along the grain boundaries of the apatite substrates without any detectable chemical reaction at 1300 and 1400 °C. Results of this study indicate that Ca 2 Yb 8 (SiO 4 ) 6 O 2 apatite has the potential to mitigate the CMAS corrosion up to about 1200 °C but not at higher temperatures.

X-ray diffraction↗
NASA NTRS2026

Thermochemical Stability of Ca2Yb8(SiO4)6O2 Apatite in Presence of Molten Calcium-Magnesium-Aluminosilicate (CMAS)

Thermochemical stability of ytterbium silicon oxyapatite Ca 2 Yb 8 (SiO 4 ) 6 O 2 (CYbS) in the presence of molten calcium-magnesium aluminosilicate (CMAS) has been investigated at elevated temperatures for consideration as a thermal and environmental barrier coating (T/EBC) material. CYbS apatite powder was synthesized from the constituent oxides via a solid-state reaction method. Hot-pressed apatite substrates were exposed to molten CMAS at 1200, 1300, and 1400 °C for 1, 10, and 50 h. Development of phases in the interaction region of the heat-treated specimens was monitored using scanning electron microscopy, transmission electron microscopy, high-angle annular dark-field imaging, selected area electron diffraction, and energy dispersive x-ray spectroscopy. Monoclinic cyclosilicate Ca 3 Yb 2 (Si 3 O 9 ) 2 formed from interaction of CYbS apatite with CaO in the CMAS melt at the apatite-CMAS reaction front and continued to nucleate and grow within the residual CMAS in diffusion couples annealed for 1 to 50 h at 1200 °C as well as in those heat treated at 1300 °C for 1 h. Residual CMAS was depleted of Ca when cyclosilicate was present. Dendritic wollastonite (CaSiO3) was observed within the residual CMAS in couples annealed at 1200 and 1300 °C. Ingress of molten CMAS, because of its exponential decrease in viscosity, occurred through open pores and along the grain boundaries of the apatite substrates without any detectable chemical reaction at 1300 and 1400 °C. Results of this study indicate that Ca 2 Yb 8 (SiO 4 ) 6 O 2 apatite has the potential to mitigate the CMAS corrosion up to about 1200 °C but not at higher temperatures.

Narottam P Bansal↗
DOE OSTI2023

Additives for high voltage lithium ion batteries

This invention relates to an electrolyte composition for a lithium ion battery comprising a lithium salt in a non-aqueous solvent containing an additive comprising a compound of formula R 3 SiOP(O) n F 2 ; wherein each R independently is a hydrocarbyl group; and n is 0 or 1; and wherein the additive is substantially free from (R 3 SiO) 3 P(O) n and (R 3 SiO) 2 P(O) n F. Electrochemical cells and batteries also are described.

Peebles, Cameron↗
DOE OSTI2020

Influence of Ag metal dispersion on the thermal conversion of ethanol to butadiene over Ag-ZrO 2 /SiO 2 catalysts

Atomistic scale models were developed and coupled with experimental investigation to deliver a functional understanding of catalytic activity and selectivity in the conversion of ethanol to 1,3-butadiene over Ag/ZrO 2 /SiO 2 . A detailed evaluation of the structural and electronic properties of the resultant catalyst models led to the identification of critical active sites of the catalyst. More importantly, the extent of Ag dispersion on the SiO 2 support and relative proximity to ZrO 2 were found to vary with the oxidation state of Ag and local coordination environment (Ag-O SiO2 ) allowing for critical control of ethanol conversion towards butadiene or ethylene. Simulations revealed that less dispersed or clustered Ag contain predominantly Ag 0 charge state and promote conversion of ethanol to ethylene. The well-dispersed Ag/ZrO 2 /SiO 2 catalyst instead contain a larger fraction of cationic Ag δ+ , and predominantly promote ethanol dehydrogenation and subsequent production of butadiene. The theoretical insights drawn were validated and confirmed experimentally using TEM, XRD and reactivity measurements demonstrating the effect of Ag dispersion on the selectivity of ethanol conversion.

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

Manufacturing of Continuous Core–Shell Hydrated Salt Fibers for Room Temperature Thermal Energy Storage

The encapsulation of salt hydrate phase change materials (PCMs) in uniform microscale bodies has yet been reported in research due in part to the delicate relationship between thermal performance and water-to-salt ratios which are easily altered during manufacturing. Herein, core–shell composite fibers comprised of a salt hydrate PCM core and a poly(acrylonitrile) (PAN) shell are wet spun in a continuous process using a syringe pump and coaxial die. The PCM phase comprises calcium chloride hexahydrate (CaCl 2 ·6H 2 O) with strontium chloride hexahydrate(SrCl 2 ·6H 2 O) (3 wt%) and fumed silica(SiO 2 ) (2 wt%) as additive, a composition that is prepared from homogenous melt at 40 °C. 15 wt% PAN in dimethylsulfoxide solvent is used to prepare the shell-forming polymer gel. PCM and polymer gel injection rates of 10–40 mL h –1 are used to spin coaxial fibers through a coagulation bath, yielding continuous microtubules with diameters in the range of 850–1500 μm. Cyclic testing shows that after 1000 cycles, melting enthalpies incurred only a 3.5% decline from 131.46 to 126.9 J g –1 . In conclusion, success here overcomes several coincidental drawbacks of PCM fiber performance and manufacturing and delivers the first example of scalable roll-to-roll PCM fiber produced by wet spinning for building material applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Impacts of Bond Type and Grafting Density on the Thermal, Structural, and Transport Behaviors of Nanoparticle Organic Hybrid Materials–Based Electrolytes

Nanoscale Organic Hybrid Materials (NOHMs) consist of polymers tethered to a nanoparticle surface, and NOHMs formed with an ionic bond between the polymer and nanoparticle have been proposed for electrochemical applications. NOHMs exhibit negligible vapor pressure, chemical tunability, oxidative thermal stability, and high ionic conductivity making them attractive in reactive and separation systems. In this study, NOHMs are synthesized by tethering Jeffamine M2070 (HPE) to SiO 2 nanocores via ionic (NOHM-I-HPE) and covalent (NOHM-C-HPE) bonding to investigate the effect of the bond type on the thermal, structural and transport properties of the tethered HPE. In the neat state, NOHM-C-HPE displays the highest thermal stability in a nitrogen atmosphere, while NOHM-I-HPE is the most stable under oxidative conditions. Small-angle neutron scattering (SANS) reveals the presence of multiple types of HPE polymers in aqueous solutions of NOHM-I-HPE (i.e., tethered, interacting, and free), whereas only tethered HPE is observed in NOHM-C-HPE systems. Moreover, the SANS profiles identify clustering of NOHM-C-HPE in aqueous solutions, but not in the corresponding NOHM-I-HPE solutions, suggesting that the free HPE chains stabilize the dispersion of NOHM-I-HPE. Furthermore, the results of this study elucidate how the bond type and grafting density can be used to tune the properties of NOHMs.

25 ENERGY STORAGE↗
DOE OSTI2023

Highly Tunable Syngas Product Ratios Enabled by Novel Nanoscale Hybrid Electrolytes Designed for Combined CO 2 Capture and Electrochemical Conversion

Coupling renewable energy with the electrochemical conversion of CO 2 to chemicals and fuels has been proposed as a strategy to achieve a new circular carbon economy and help mitigate the effects of anthropogenic CO 2 emissions. Liquid-like Nanoparticle Organic Hybrid Materials (NOHMs) are composed of polymers tethered to nanoparticles and are previously explored as CO 2 capture materials and electrolyte additives. Here, in this study, two types of aqueous NOHM-based electrolytes are prepared to explore the effect of CO 2 binding energy (i.e., chemisorption versus physisorption) on CO 2 electroreduction over a silver nanoparticle catalyst for syngas production. Poly(ethylenimine) (PEI) and Jeffamine M2070 (HPE) are ionically tethered to SiO 2 nanoparticles to form the amine-containing NOHM-I-PEI and ether-containing NOHM-I-HPE, respectively. At less negative cathode potentials, PEI and NOHM-I-PEI-based electrolytes produce CO at higher rates than 0.1 molal. KHCO 3 due to favorable catalyst-electrolyte interactions. Whereas at more negative potentials, H 2 production is favored because of the carbamate electrochemical inactivity. Conversely, HPE and NOHM-I-HPE-based electrolytes display poor CO 2 reduction performance at less negative potentials. At more negative potentials, their performance approached that of 0.1 molal. KHCO 3 , highlighting how the polymer functional groups of NOHMs can be strategically selected to produce value-added products from CO 2 with highly tunable compositions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Long–Cycling Sulfide–Based All–Solid–State Batteries Enabled by Electrochemo–Mechanically Stable Electrodes

Anode significantly determines the energy density of all-solid-state Lithium batteries (ASLBs). Silicon (Si) and Lithium (Li) metal are two of the most attractive anodes because of their ultrahigh theoretical capacities. However, most investigations focus on Li metal; the great potential of Si is underrated. This study investigates Si anode's stability, processability, and cost in ASLBs and compares them with Li metal. Moreover, the single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O 2 is stabilized with a lithium silicate (Li 2 SiO x ) through a scalable sol-gel method. ASLBs with a cell-level energy density of 285 Wh kg -1 are obtained through sandwiching Si anode, thin sulfide solid-state electrolyte membrane, and interface stabilized LiNi 0.8 Co 0.1 Mn 0.1 O 2 . The full cell delivered a high capacity of 145 mAh g -1 at C/3 and maintained stability for 1000 cycles. This work inspires commercializing the ASLBs on a large scale with exciting manufacturing lines for large-scale, safe, and economical energy storage.

25 ENERGY STORAGE↗
DOE OSTI2021

Non-Contact Mass Density and Thermal Conductivity Measurements of Organic Thin Films Using Frequency–Domain Thermoreflectance

Thin-film organic materials are broadly used to study amorphous stabilization of active pharmaceuticals, control explosive detonation phenomena, and introduce insulation in novel thermal barriers. Their synthesis, however, introduces defects and thickness variations that warrant careful characterization of local thermophysical properties such as thermal conductivity and mass density. In this study, wide bandwidth (200 Hz to 20 MHz) frequency–domain thermoreflectance (FDTR) is demonstrated to simultaneously extract the thermal conductivity and mass density of 1 μm physical vapor-deposited indomethacin films on Si and SiO 2 substrates, as well as 10 and 100 μm films on Si. By assuming a bulk specific heat capacity, mass densities are determined with FDTR measurements of volumetric heat capacity and are in good agreement with the literature, as well as models based upon a dependence on porosity and the kinetic theory for phonons. Lastly, it is found that for broad-band FDTR measurements, insulating substrates provide improved fidelity for the extraction of thermal conductivity and volumetric heat capacity in organic thin films. Overall, this work demonstrates the potential for FDTR as a non-contact method to determine microscale mass density variations across the surface and thickness of organic thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Measuring the Exciton Binding Energy: Learning from a Decade of Measurements on Halide Perovskites and Transition Metal Dichalcogenides

The exciton binding energy ( E b ) is a key parameter that governs the physics of many optoelectronic devices. At their best, trustworthy and precise measurements of E b challenge theoreticians to refine models, are a driving force in advancing the understanding of a material system, and lead to efficient device design. At their worst, inaccurate E b measurements lead theoreticians astray, sow confusion within the research community, and hinder device improvements by leading to poor designs. Here, this review article seeks to highlight the pros and cons of different measurement techniques used to determine E b , namely, temperature‐dependent photoluminescence, resolving Rydberg states, electroabsorption, magnetoabsorption, scanning tunneling spectroscopy, and fitting the optical absorption. Due to numerous conflicting E b values reported for halide perovskites (HP) and transition metal dichalcogenides (TMDC) monolayers, an emphasis is placed on highlighting these measurements in an attempt to reconcile the variance between different measurement techniques. It is argued that the experiments with the clearest indicators are in agreement on the following values: ≈350–450 meV for TMDC monolayers between SiO 2 and vacuum, ≈150–200 meV for hBN‐encapsulated TMDC monolayers, ≈200–300 meV for common lead‐iodide 2D HPs, and ≈10 meV for methylammonium lead iodide.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Sulfurization Engineering of One–Step Low–Temperature MoS 2 and WS 2 Thin Films for Memristor Device Applications

2D materials have been of considerable interest as new materials for device applications. Non-volatile resistive switching applications of MoS 2 and WS 2 have been previously demonstrated; however, these applications are dramatically limited by high temperatures and extended times needed for the large-area synthesis of 2D materials on crystalline substrates. The experimental results demonstrate a one-step sulfurization method to synthesize MoS 2 and WS 2 at 550 °C in 15 min on sapphire wafers. Furthermore, a large area transfer of the synthesized thin films to SiO 2 /Si substrates is achieved. Following this, MoS 2 and WS 2 memristors are fabricated that exhibit stable non-volatile switching and a satisfactory large on/off current ratio (10 3 –10 5 ) with good uniformity. Tuning the sulfurization parameters (temperature and metal precursor thickness) is found to be a straightforward and effective strategy to improve the performance of the memristors. Furthermore, the demonstration of large-scale MoS 2 and WS 2 memristors with a one-step low-temperature sulfurization method with simple strategy to tuning can lead to potential applications such as flexible memory and neuromorphic computing.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Lossless Phonon Transition Through GaN‐Diamond and Si‐Diamond Interfaces

Abstract Advancing Silicon (Si) technology beyond Moore's law through 3D architectures requires highly efficient heat management methods compatible with foundry processes. While continued increases in transistor density can be achieved through 3D architectures, self‐heating in the upper tiers degrades the performance. Self‐heating is a critical problem for high‐power, high‐frequency, wide bandgap, and ultra‐wide bandgap devices as well. Diamond, known for its exceptional thermal conductivity, offers a viable solution in both these cases. Since thermal boundary resistance (between the channel/junction and diamond plays a crucial role in overall thermal resistance, this study investigates various dielectrics for interface engineering, such as Silicon dioxide (SiO 2 ), amorphous‐ Silicon Carbide (a‐SiC), and Silicon Nitride (SiN x ), to make a phonon bridge at gallium nitride (GaN)‐diamond and Si‐diamond interfaces. The a‐SiC interlayer reduces diamond/GaN (<5 m 2 K per GW) and diamond/Si (<2 m 2 K per GW) thermal boundary resistances by linking low‐ and high‐frequency phonons, boosting phonon transport through the interface. Engineered interfaces enhance heat spreading from the channel/junction and rule out premature failure.

Malakoutian, Mohamadali↗
DOE OSTI2024

Size Effect of Negative Capacitance State and Subthreshold Swing in Van der Waals Ferrielectric Field–Effect Transistors

Analytical calculations corroborated by the finite element modeling show that thin films of Van der Waals ferrielectrics covered by a 2D-semiconductor are promising candidates for the controllable reduction of the dielectric layer capacitance due to the negative capacitance (NC) effect emerging in the thin films. The NC state is conditioned by energy-degenerated poly-domain states of the ferrielectric polarization induced in the films under incomplete screening conditions in the presence of a dielectric layer. Calculations performed for the FET-type heterostructure “ferrielectric CuInP 2 S 6 film—2D-MoS 2 single-layer—SiO 2 dielectric layer” reveal the pronounced size effect of the multilayer capacitance. Derived analytical expressions for the electric polarization and multilayer capacitance allow to predict the thickness range of the dielectric layer and ferrielectric film for which the NC effect is the most pronounced in various Van der Waals ferrielectrics, and the corresponding subthreshold swing becomes much less than the Boltzmann's limit. Obtained results can be useful for the size and temperature control of the NC effect in the steep-slope ferrielectric FETs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Silicon Anodes with Improved Calendar Life Enabled By Multivalent Additives

Silicon is widely recognized as the most promising upgrade for graphite anodes due to its much higher capacity, natural abundance, and ability to be directly applied in the slurry-based, roll-to-roll production lines. However, in addition to the fast capacity decay, silicon anodes also suffer from inferior calendar life in practical applications due to the unstable solid-electrode interface (SEI). Until now, strategies to effectively improve the calendar life by tailored SEIs remain largely unclear, especially in high-Si content, zero-graphite anodes. Here, silicon anodes with superior calendar life are developed by adding small concentrations of multivalent salts into the baseline electrolyte. The Ca additive reacts with the F ions in the electrolyte, forming a layer of nanocrystalline CaF 2 that is closely coated around the silicon particles. The CaF 2 -enabled new SEI is strong and dense, which effectively protects the silicon core from side reactions, leading to lower capacity decay after calendar aging at high voltage. More importantly, the Ca additive is effective universally for all available commercial silicon or SiO sources. This study provides a feasible and low-cost solution for developing silicon anodes with long calendar life, paving the way towards commercially viable silicon anodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Insights into the Crossover Effects in Cells with High‐Nickel Layered Oxide Cathodes and Silicon/Graphite Composite Anodes

Abstract Silicon anodes are regarded as one of the most promising alternatives to graphite (Gr) anodes due to their ultrahigh capacity, abundance, and low cost. Coupling Si‐based anodes with high‐nickel layered oxide cathodes LiNi x Mn y Co 1− x − y O 2 (NMC, x ≥ 0.8) can enhance the driving range for electric vehicles. Transition‐metal (TM) ion dissolution and deposition has been a long‐known failure mode for Gr‐based lithium‐ion batteries. However, the mechanistic insight associated with TM ion deposition on Si‐based anodes has rarely been reported. Herein, the impact of in situ deposited TM ions on SiO x /Gr composite anodes and the individual influences of Ni, Mn, and Co on the structural and electrochemical stability along with the underlying degradation mechanisms are presented. TM ion dissolution causes a greater deleterious impact on Si than on Gr, with different TM ions exhibiting different influences on anode‐electrolyte interphase formation. Specifically, Ni deposit induces more aggressive salt decomposition; Co deposit has negligible effect on salt decomposition, but significantly accelerates solvent decomposition; and Mn deposit aggravates both salt and solvent decompositions, resulting in worse full cell performance. The extent of degradation decreases in the order Mn 2+ > Ni 2+ > Co 2+ . The systematic comparisons presented can guide further development of high energy systems.

Zhang, Xianhui↗
DOE OSTI2021

Effects of surface species and homogeneous reactions on rates and selectivity in ethane oxidation on oxide catalysts

Selective alkane oxidations on metal oxide catalysts involve complex mechanisms with multiple reactions in series and parallel, different types of reduced and oxidized surface species, and potential contributions from gas-phase reactions. We report kinetics and thermodynamics of elementary steps involved in C 2 H 6 -O 2 reactions on SiO 2 -supported small vanadium oxide domains are determined using density functional theory. These surface reactions together with gas-phase mechanisms are incorporated in kinetic simulations to determine how surface and gaseous reactions interact and contribute to rates and selectivity. The results show that gas-phase reactions within pore volumes in contact with the catalyst contribute significantly to C 2 H 6 activation rates, even at conditions where gas-phase reactions in empty volumes without catalyst are negligible. The majority of C 2 H 6 activations occur on the surface, via H abstraction by vanadium oxo species present at terminal lattice oxygens. The gas-phase activations via H-abstraction by OH radicals also exhibit significant contributions. The reduced centers formed by reactions at vanadium oxo species are re-oxidized rapidly and, therefore, are present in very small concentrations at reaction conditions. The re-oxidation steps lead to the formation of HO 2 radicals and surface peroxo species that are also rapidly consumed and are present in small concentrations. The peroxo species preferentially convert C 2 H 4 to its epoxide product and influence selectivity even at low concentrations. The gas-phase reactions decrease the concentrations of peroxo species and improve selectivity slightly. The effects of reaction conditions and catalyst site density provide further insights into how factors beyond conversions at lattice oxygens influence rates and selectivity in alkane oxidation reactions of significant industrial importance.

42 ENGINEERING↗