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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Tetracene Functionalized Si(111) Achieves Enhanced Solar-to-Chemical Energy Conversion via Molecular Acceptor States

The properties of semiconductor|liquid interfaces play a critical role in determining the efficiency of solar-to-hydrogen (STH) conversion. Here, we investigate how molecular functionalization of Si(111) and Si(111)|TiO 2 surfaces impacts photoelectrochemical (PEC) hydrogen production efficiency. We find that functionalization of ∼3% of the atop sites of Si(111) with either 9-anthracene (Anth) or 5-tetracene (Tet), with the remaining sites passivated by methyl groups, provides substrates with high electronic quality and low surface oxide densities, as determined by X-ray photoelectron spectroscopy (XPS) measurements. Surface photovoltage (SPV) spectroscopy shows that surfaces modified with Anth or Tet exhibit an increased photovoltage, with Tet-functionalized surfaces yielding an additional 192 meV relative to methyl-terminated Si(111), indicating improved charge separation for Si-Tet. Further improvement in onset potential was achieved by replacing a nitrogen-containing TiO 2 atomic layer deposition (ALD) precursor (TDMAT) with a precursor lacking nitrogen (TTIP), which eliminates the parasitic defect band in the TiO 2 overlayer (p-Si(111)-Tet|TTIP-TiO 2 |Pt: V OC = +0.283 ± 0.041 V vs RHE). Density functional theory (DFT) analysis demonstrates that compared with Anth-modified Si(111), the Tet-modified surface exhibits more hybridized Si(111)-Tet states closer to the silicon band edges. Mercury contact current–voltage (I–V, dark) measurements quantified the relative interfacial density of states of Si-Tet, Si-Anth and Si-Me surfaces─revealing that the interfacial state density was highest for Si-Tet. This suggests that such hybridized interfaces serve to capture better photoexcited charge, which enables facile electron transfer to molecular acceptors in solution. Altogether, the data indicate that beneficial hybrid molecular LUMO surface states interacting with the Si conduction band edge results in improved hydrogen evolution (HER) performance for p-Si devices.

Group theory↗
DOE OSTI2021

Renewable fatty acid ester production in Clostridium

Abstract Bioproduction of renewable chemicals is considered as an urgent solution for fossil energy crisis. However, despite tremendous efforts, it is still challenging to generate microbial strains that can produce target biochemical to high levels. Here, we report an example of biosynthesis of high-value and easy-recoverable derivatives built upon natural microbial pathways, leading to improvement in bioproduction efficiency. By leveraging pathways in solventogenic clostridia for co-producing acyl-CoAs, acids and alcohols as precursors, through rational screening for host strains and enzymes, systematic metabolic engineering-including elimination of putative prophages, we develop strains that can produce 20.3 g/L butyl acetate and 1.6 g/L butyl butyrate. Techno-economic analysis results suggest the economic competitiveness of our developed bioprocess. Our principles of selecting the most appropriate host for specific bioproduction and engineering microbial chassis to produce high-value and easy-separable end products may be applicable to other bioprocesses.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Bimetallic Ir x Pb nanowire networks with enhanced electrocatalytic activity for the oxygen evolution reaction

Metallic nanowire networks (MNNs) have attracted increasing attention due to their high surface area and tunable compositions. Although enormous efforts have been devoted to preparing noble metal MNNs with different compositions, the composition optimization and the formation mechanism of Ir-based MNNs have not been thoroughly investigated. Here, this work presents a facile method for synthesizing robust Ir-based bimetallic MNNs by chemical reduction. As unveiled by our characterization, the network structure is constructed by ultrafine nanowires evolved from aggregated nanoparticles. The element analysis confirms the even distribution of Pb and Ir elements. The introduction of Pb is found to be beneficial to the stable formation of Ir x Pb MNNs in the sol–gel process. By tuning the precursor ratio of Ir and Pb, the optimized Ir x Pb catalyst delivers an enhanced oxygen evolution reaction (OER) performance in acid media (307 mV at 10 mA cm −2 ), which is superior to that of the commercial IrO 2 catalyst. Besides, due to the robust structure of the Ir x Pb MNNs, excellent OER durability is observed in the accelerated durability test (ADT) (2000 cycles).

Bimetallic↗
DOE OSTI2020

High-capacity rotary drum for atomic layer deposition onto powders and small mechanical parts in a hot-walled viscous flow reactor

Atomic layer deposition (ALD) is uniquely capable of providing uniform thin-film coatings on powder substrates, but powder processing has historically required an ALD reactor designed specifically for powders-e.g., a fluidized bed. Tubular hot-walled viscous-flow reactors commonly employed in laboratory-scale ALD research for coating planar substrates such as silicon have been employed previously to coat gram quantities of powder spread out in a thin layer on a tray, but larger quantities of powder introduce long diffusion pathways where reactants are unable to percolate to the bottom of the powder bed to provide uniform coating in reasonable time periods. In this work, we report a rotary drum with a capacity of 100s of grams that is compatible with conventional tubular hot-walled ALD reactors and provides uniform coatings on powders in viscous flow operation. We benchmark this system using Al 2 O 3 ALD with trimethylaluminum and water. We examine the effect of rotation speed and powder quantity on saturation time via in situ quadrupole mass spectroscopy measurements and gravimetric analysis. Finally, the rotary drum we report is able to provide homogenous coating of up to 75g of silica gel powder with a total surface area of similar to 1500m 2 in viscous flow operation with precursor utilization as high as 70%.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Studies on atomic layer deposition of IRMOF-8 thin films

Deposition of IRMOF-8 thin films by atomic layer deposition was studied at 260–320 °C. Zinc acetate and 2,6-naphthalenedicarboxylic acid were used as the precursors. The as-deposited amorphous films were crystallized in 70% relative humidity at room temperature resulting in an unknown phase with a large unit cell. An autoclave with dimethylformamide as the solvent was used to recrystallize the films into IRMOF-8 as confirmed by grazing incidence x-ray diffraction. The films were further characterized by high temperature x-ray diffraction (HTXRD), field emission scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), time-of-flight elastic recoil detection analysis (TOF-ERDA), nanoindentation, and energy-dispersive x-ray spectroscopy. HTXRD measurements revealed similar behavior to bulk IRMOF-8. According to TOF-ERDA and FTIR, composition of the films was similar to IRMOF-8. Through-porosity was confirmed by loading the films with palladium using Pd(thd){sub 2} (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) as the precursor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Effect of annealing temperature on titania nanoparticles

Titania polycrystalline samples are prepared by using sol-gel route hydrolyzing a alkoxide titanium precursor under acidic conditions. The as prepared samples are treated with different calcination temperatures. The anatase phase of titania forms when treated below 600°C, above that temperature the anatase phase tends to transform into the rutile phase of titania. The experimental determination of average grain size, phase formation, lattice parameters and the crystal structures of titania samples at different calcinations is done using X-ray diffraction (XRD). Fourier Transform Infra-red Spectroscopy (FTIR), UV-vis-NIR spectroscopy and Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis X-ray are used to characterize the samples to bring impact on the respective properties.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Incorporation of lead and titanium into a porous alumina membrane during Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3} nanotube synthesis

We report the identification and characteristics of lead aluminate (Pb{sub 2}Al{sub 2}O{sub 5} or PbAl{sub 12}O{sub 19})/aluminum titanate (Al{sub 2}TiO{sub 5}) formed as a result of the interaction between a Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3} (PZT) precursor and a porous alumina membrane (PAM) during PZT nanotube synthesis. The surface morphology and composition of PZT nanotubes were examined as a function of the etching time and annealing temperature, and the diffusion of elements over nanometer length scales during PZT nanotube formation was investigated based on analysis using field emission transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray microscopy. As the annealing temperature increased, the volume of lead aluminate/aluminum titanate increased, suggesting that considerable diffusion of Pb and Ti occurred and, in turn, dramatically affected the nanotube characteristics. The diffusion of Pb and Ti was clearly evident, resulting in the formation of a distinct lead aluminate/aluminum titanate at the PZT nanotube/PAM interface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Effectiveness of CID, HCD, and ETD with FT MS/MS for Degradomic-Peptidomic Analysis: Comparison of Peptide Identification Methods

We report on use of an Orbitrap Velos mass spectrometer for comparison of fragmentation methods namely CID-, HCD-, and ETD for FT MS/MS analysis of human blood plasma peptidomic peptides. The peptidomic peptides were able to be identified from CID, HCD, and ETD spectra on specific confidence levels (e.g., 1% false discovery rate) with use of conventional SEQUEST database search software, and the number of identified peptides was increased by ~50% using accurate fragments (e.g., with mass tolerance of 0.05Da) in comparison with traditional moderate accuracy fragments (e.g., with 1 Da mass tolerance) for database search. However, the peptide datasets identified with such decoy search strategy were found to be varied by ~25% in the dataset size and ~20% in the dataset content with type of decoy database and precursor mass tolerances used for database search. CID was evaluated as the largest contributor to the identified peptide datasets, and HCD, and ETD provided ~20% and ~22% respectively additional peptides with accurate fragments for peptide identification, in contrast to ~25% and ~13% respectively with use of moderate accuracy fragments. When long (typically ≥7 amino acids) sequences were used for identification of peptides from the previously published UStags and de novo sequencing methods, HCD was evaluated as the largest contributor, and CID and ETD provided ~26% and ~8% respectively additional peptides from the UStags method and ~26% and ~6% respectively additional peptides from the de novo sequencing method. The peptide datasets identified with the UStags method were little influenced by the decoy database and mass tolerance and 98-99% peptide overlaps could be achieved between these datasets. CID, HCD, and ETD contributed their identifications of various charge state peptides in the m/z range highly overlapped and complementary implementation of CID, HCD, and ETD should be applied to maximize the number of peptides identified. Finally, the investigation presented in this work suggests that selection of fragmentation methods benefits significantly from a careful match with data analysis method applied for identification of peptides and the analysis throughput desired for various purposes of peptidomic-degradomic analysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Identification and Mitigation of Generated Solid By-Products during Advanced Electrode Materials Processing

A scalable, solid-state elevated temperature process was developed to produce high capacity carbonaceous electrode materials for energy storage devices via decomposition of starch-based precursor in an inert atmosphere. The fabricated carbon-based architectures are useful as an excellent electrode material for lithium-ion, sodium-ion and lithium-sulfur batteries. This article focuses on the study and analysis of the formed nanometer-sized byproducts during the lab-scale production of carbonaceous electrode materials in the process design phase. The complete material production process was studied by operation, namely during heating, holding the reaction at elevated temperature, followed by cooling. The unknown downstream particles in the process exhaust were collected and characterized via aerosol and liquid suspensions, and they were quantified using direct-reading instruments for number and mass concentrations. The airborne emissions were collected on polycarbonate filters and TEM grids using the Tsai diffusion sampler (TDS) for characterization and further analysis. Released byproduct aerosols collected in a deionized (DI) water trap were analyzed using a Nanosight real time nanoparticle characterization system and the aerosols emitted post water suspension were collected and characterized. Individual particles in the nanometer size range were found in exhaust aerosols, however, crystal structured aggregates were formed on the sampling substrate after a long-term sampling of emitted exhaust. After characterizing the released aerosol byproducts, methods were also identified to mitigate possible human and environmental exposures upon the industrial implementation of such a process.

25 ENERGY STORAGE↗
DOE OSTI2024

Facile electrocatalytic proton reduction by a [Fe–Fe]-hydrogenase bio-inspired synthetic model bearing a terminal CN — ligand

An azadithiolate bridged CN — bound pentacarbonyl bis-iron complex, mimicking the active site of [Fe–Fe] H 2 ase is synthesized. The geometric and electronic structure of this complex is elucidated using a combination of EXAFS analysis, infrared and Mössbauer spectroscopy and DFT calculations. The electrochemical investigations show that complex 1 effectively reduces H + to H 2 between pH 0–3 at diffusion-controlled rates (10 11 M —1 s —1 ) i.e. 10 8 s —1 at pH 3 with an overpotential of 140 mV. Electrochemical analysis and DFT calculations suggests that a CN— ligand increases the p K a of the cluster enabling hydrogen production from its Fe(I)–Fe(0) state at pHs much higher and overpotential much lower than its precursor bis-iron hexacarbonyl model which is active in its Fe(0)–Fe(0) state. The formation of a terminal Fe–H species, evidenced by spectroelectrochemistry in organic solvent, via a rate determining proton coupled electron transfer step and protonation of the adjacent azadithiolate, lowers the kinetic barrier leading to diffusion controlled rates of H 2 evolution. The stereo-electronic factors enhance its catalytic rate by 3 order of magnitude relative to a bis-iron hexacarbonyl precursor at the same pH and potential.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Analysis of fluid fuel flow to the neutron kinetics on molten salt reactor FUJI-12

Molten Salt Reactor is a reactor are operating with molten salt fuel flowing. This condition interpret that the neutron kinetics of this reactor is affected by the flow rate of the fuel. This research analyze effect by the alteration velocity of the fuel by MSR type Fuji-12, with fuel composition LiF-BeF{sub 2}-ThF{sub 4}-{sup 233}UF{sub 4} respectively 71.78%-16%-11.86%-0.36%. Calculation process in this study is performed numerically by SOR and finite difference method use C programming language. Data of reactivity, neutron flux, and the macroscopic fission cross section for calculation process obtain from SRAC-CITATION (Standard thermal Reactor Analysis Code) and JENDL-4.0 data library. SRAC system designed and developed by JAEA (Japan Atomic Energy Agency). This study aims to observe the effect of the velocity of fuel salt to the power generated from neutron precursors at fourth year of reactor operate (last critical condition) with number of multiplication effective; 1.0155.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

Growth and properties of crystalline CuInSe{sub 2} thin films by SPD technique

CuInSe{sub 2} thin films were grown on glass substrates using the chemical spray pyrolysis technique. The CuInSe{sub 2} films were co-deposited from aqueous solutions containing CuCl{sub 2}, InCl{sub 3}, and SeO{sub 2} used as Cu, In and Se precursors respectively. EDC was used as a complexing agent and films were grown at the constant temperature of 270°C. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy dispersive analysis of X-rays (EDAX) and the results indicate that the films are single phase, p-type in conductivity and have the chalcopyrite structure. Optical study shows that the optical band gap value is 1.03 eV. From the XRD study it is clear that the average crystallite size of the films is in the range 50 to 70 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Local orbital degeneracy lifting as a precursor to an orbital-selective Peierls transition

Fundamental electronic principles underlying all transition metal compounds are the symmetry and filling of the d-electron orbitals and the influence of this filling on structural configurations and responses. Here we use a sensitive local structural technique, x-ray atomic pair distribution function analysis, to reveal the presence of fluctuating local-structural distortions at high temperature in one such compound, CuIr 2 S 4 . We show that this hitherto overlooked fluctuating symmetry-lowering is electronic in origin and will modify the energy-level spectrum and electronic and magnetic properties. The explanation is a local, fluctuating, orbital-degeneracy-lifted state. The natural extension of our result would be that this phenomenon is likely to be widespread amongst diverse classes of partially filled nominally degenerate d-electron systems, with potentially broad implications for our understanding of their properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Modified Point-Kinetics Model for Neutron Precursors and Fission Product Behavior for Fluid-Fueled Molten Salt Reactors

Fluid-fueled nuclear reactors, such as molten salt reactors (MSRs), have recently gained significant interest. These advanced reactors represent a potential revolutionary shift in the implementation of nuclear power, and as a broad class of reactors, they have the potential to directly address many U.S. energy policy objectives. Fuel that is dissolved in the coolant requires methods to account for the birth, decay, and transport of fission products not only in the core but also throughout the loop and any auxiliary systems, such as off-gas, to which liquid fuel flows, gaseous products are carried, or solid particulates plate out. System models are particularly well suited to explore the wide range of phenomena that are associated with fluid-fueled systems, especially for safeguards analysis. However, before system dynamics can be explored, the compositions of fission products of the salt throughout the loop must be determined as they drive the dynamic behavior of a reactor.This paper describes the derivation of a modified point-kinetics model for obtaining a first-order approximation of the behavior of a salt-fueled system in which neutron precursors and fission products are born in the fuel-salt and transported outside the core. This paper also provides verification of the model using a steady-state analytic solution and provides additional cases exploring the response under transient cases. This model establishes a baseline model that can be used to explore the dynamic response of fluid-fueled reactors and to investigate important safeguards issues such as mass accountability of source terms. Here, the model is implemented in the Oak Ridge National Laboratory–developed, Modelica-based TRANSFORM library that was developed to investigate various aspects of advanced energy systems.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

13 C Metabolic Flux Analysis for Systematic Metabolic Engineering of S. cerevisiae for Overproduction of Fatty Acids

Efficient redirection of microbial metabolism into the abundant production of desired bioproducts remains non-trivial. Here, we used flux-based modeling approaches to improve yields of fatty acids in Saccharomyces cerevisiae. We combined 13 C labeling data with comprehensive genome-scale models to shed light onto microbial metabolism and improve metabolic engineering efforts. We concentrated on studying the balance of acetyl-CoA, a precursor metabolite for the biosynthesis of fatty acids. A genome-wide acetyl-CoA balance study showed ATP citrate lyase from Yarrowia lipolytica as a robust source of cytoplasmic acetyl-CoA and malate synthase as a desirable target for downregulation in terms of acetyl-CoA consumption. These genetic modifications were applied to S. cerevisiae WRY2, a strain that is capable of producing 460 mg/L of free fatty acids. With the addition of ATP citrate lyase and downregulation of malate synthase, the engineered strain produced 26% more free fatty acids. Further increases in free fatty acid production of 33% were obtained by knocking out the cytoplasmic glycerol-3-phosphate dehydrogenase, which flux analysis had shown was competing for carbon flux upstream with the carbon flux through the acetyl-CoA production pathway in the cytoplasm. In total, the genetic interventions applied in this work increased fatty acid production by ~70%.

-omics data↗
DOE OSTI2015

Structural evolution in the crystallization of rapid cooling silver melt

The structural evolution in a rapid cooling process of silver melt has been investigated at different scales by adopting several analysis methods. The results testify Ostwald’s rule of stages and Frank conjecture upon icosahedron with many specific details. In particular, the cluster-scale analysis by a recent developed method called LSCA (the Largest Standard Cluster Analysis) clarified the complex structural evolution occurred in crystallization: different kinds of local clusters (such as ico-like (ico is the abbreviation of icosahedron), ico-bcc like (bcc, body-centred cubic), bcc, bcc-like structures) in turn have their maximal numbers as temperature decreases. And in a rather wide temperature range the icosahedral short-range order (ISRO) demonstrates a saturated stage (where the amount of ico-like structures keeps stable) that breeds metastable bcc clusters. As the precursor of crystallization, after reaching the maximal number bcc clusters finally decrease, resulting in the final solid being a mixture mainly composed of fcc/hcp (face-centred cubic and hexagonal-closed packed) clusters and to a less degree, bcc clusters. This detailed geometric picture for crystallization of liquid metal is believed to be useful to improve the fundamental understanding of liquid–solid phase transition. - Highlights: • A comprehensive structural analysis is conducted focusing on crystallization. • The involved atoms in our analysis are more than 90% for all samples concerned. • A series of distinct intermediate states are found in crystallization of silver melt. • A novelty icosahedron-saturated state breeds the metastable bcc state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗