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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Atmospheric-pressure glow plasma synthesis of plasmonic and photoluminescent zinc oxide nanocrystals

In this paper, we present a large-volume (non-micro) atmospheric pressure glow plasma capable of rapid, large-scale zinc oxide nanocrystal synthesis and deposition (up to 400 μg/min), whereas in the majority of the literature, nanoparticles are synthesized using micro-scale or filamentary plasmas. The reactor is an RF dielectric barrier discharge with a non-uniform gap spacing. This design encourages pre-ionization during the plasma breakdown, making the discharge uniform over a large volume. The produced zinc oxide nanocrystals typically have diameters ranging from 4 to 15 nm and exhibit photoluminescence at ≈550 nm and localized surface plasmon resonance at ≈1900 cm{sup −1} due to oxygen vacancies. The particle size can be tuned to a degree by varying the gas temperature and the precursor mixing ratio.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Mapping growth windows in quaternary perovskite oxide systems by hybrid molecular beam epitaxy

Requisite to growing stoichiometric perovskite thin films of the solid-solution A ' 1-x A x B O 3 by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'B O 3 and AB O 3 , which can be grown in a self-regulated fashion, but under different conditions. Using the example of La 1-x Sr x VO 3 , the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x , was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found that the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x . This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A ' 1-x A x B O 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2022

Metal Oxide Varistor (MOV) Lifetime Estimation with Impulse-Based Testing in PV Inverter Systems

Surges caused by lightning strikes could damage electrical components in photovoltaic (PV) systems. Metal oxide varistors (MOVs) are commonly used to protect PV systems from lightning strikes. This paper proposes a holistic impulse-based MOV lifetime estimation framework. The impacts of peak current and fault duration induced by lightning events are considered in the MOV lifetime estimation framework. Moreover, the impact of different parameter combinations on MOV lifetime estimation is analyzed. The effectiveness of the proposed work is validated in a PV inverter test system developed in MATLAB/Simulink.

lifetime estimation↗
DOE OSTI2020

Sputtered Aluminum Oxide and p+ Amorphous Silicon Back-Contact for Improved Hole Extraction in Polycrystalline CdSexTe1-x and CdTe Photovoltaics

A thin layer of Al 2 O 3 at the back of CdSe x T e1-x /CdTe devices is shown to passivate the back interface and drastically improve surface recombination lifetimes and photoluminescent response. Despite this, such devices do not show an improvement in open-circuit voltage (VOC.) Adding a p + amorphous silicon layer behind the Al 2 O 3 bends the conduction band upward, reducing the barrier to hole extraction and improving collection. Further optimization of the Al 2 O 3 , amorphous silicon (a-Si), and indium-doped tin oxide (ITO) layers, as well as their interaction with the CdCl 2 passivation process, are necessary to translate these electro-optical improvements into gains in voltage.

14 SOLAR ENERGY↗
DOE OSTI2015

An autotrophic H 2 -oxidizing, nitrate-respiring, Tc(VII)-reducing A cidovorax sp. isolated from a subsurface oxic-anoxic transition zone: H 2 -oxidizing, Tc-reducing Acidovorax spp.

Increasing concentrations of H 2 with depth were observed across a geologic unconformity and associated redox transition zone in the subsurface at the Hanford Site in south-central Washington, USA. An opposing gradient characterized by decreasing O 2 and nitrate concentrations was consistent with microbial-catalyzed biogeochemical processes. Sterile sand was incubated in situ within a multi-level sampler placed across the redox transition zone to evaluate the potential for Tc(VII) reduction and for enrichment of H 2 -oxidizing denitrifiers capable of reducing Tc(VII). H 2 -driven TcO 4- reduction was detected in sand incubated at all depths but was strongest in material from a depth of 17.1 m. Acidovorax spp. were isolated from H 2 -nitrate enrichments from colonized sand from 15.1 m, with one representative, strain JHL-9, subsequently characterized. JHL-9 grew on acetate with either O 2 or nitrate as electron acceptor (data not shown) and on medium with bicarbonate, H 2 and nitrate. JHL-9 also reduced pertechnetate (TcO 4- ) under denitrifying conditions with H 2 as the electron donor. H 2 -oxidizing Acidovorax spp. in the subsurface at Hanford and other locations may contribute to the maintenance of subsurface redox gradients and offer the potential for Tc(VII) reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

MIS High Purity Plutonium Oxide Metal Oxidation Product MT1490 (SSR125): Final Report

A high purity plutonium dioxide material from the Material Identification and Surveillance (MIS) Program inventory has been studied with regard to gas generation and corrosion in a storage environment. Sample MT1490 represents process plutonium oxides from several metal oxidation operations that are currently stored in 3013 containers. This study followed over time, the gas pressure of a sample with nominally 0.5 weight percent water in a sealed container with an internal volume scaled to 1/500 th of the volume of a 3013 container. The sample was a mixture of as-received material, material calcined at 800°C and material calcined at 950°C. This material contained 87% plutonium with no major impurities. Gas compositions were measured periodically over a nine year period. The maximum observed gas pressure of 118 kPa was reached during the ninth year. The increase over the initial pressure of 95 kPa was primarily due to generation of nitrogen and hydrogen gas. Oxygen was a minor component of the headspace gas. At the completion of the study, the inner bucket showed signs of corrosion, including pitting, in the container material contact region.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Multi-Constituent Airborne Contaminants Capture with Low Cost Oxide Getters and Mitigation of Cathode Poisoning in Solid Oxide Fuel Cell

The technical effort and scientific findings, discussed in this report, documents operational barriers and associated long term performance stability challenges posed by the presence of trace airborne multi-constituent contaminants present in high-temperature electrochemical systems, including Solid Oxide Fuel Cells (SOFCs), Solid Oxide Electrolysis Cells (SOECs), Ion Transport Membranes, and Gas Separation systems. Above systems, offering promises for cleanliness and energy efficiency, face challenges with electrode poisoning stemming from the presence of trace contaminants including gaseous Cr/B/Si vapors in the presence of intrinsic contaminants SO 2 /CO 2 /H 2 O gases. The study indicates that the long-term electrical performance degradation in SOFC systems can be traced to electrochemical, structural, and mechanical changes across cell, stack, and balance of plant components resulting from interactions with trace contaminants leading to increase in both ohmic and non-ohmic polarizations. The degradation primarily results from solid-state and gas-phase materials migration, electrode poisoning, and interactions at the cell and stack levels. Cathode degradation emerges as a significant factor impacting overall SOFC performance, especially related to the presence of intrinsic and extrinsic airborne impurities such as SOx, CrOx(OH)y, SOx, Si(OH)x, and HBOx. Although at trace levels, prolong systems operation at higher airflow (3-10X stoichiometric) allow the accumulation of contaminants within the cell components leading to electrical performance degradation through poisoning and electrode deactivation.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2014

Band offsets of n-type electron-selective contacts on cuprous oxide (Cu{sub 2}O) for photovoltaics

The development of cuprous oxide (Cu{sub 2}O) photovoltaics (PVs) is limited by low device open-circuit voltages. A strong contributing factor to this underperformance is the conduction-band offset between Cu{sub 2}O and its n-type heterojunction partner or electron-selective contact. In the present work, a broad range of possible n-type materials is surveyed, including ZnO, ZnS, Zn(O,S), (Mg,Zn)O, TiO{sub 2}, CdS, and Ga{sub 2}O{sub 3}. Band offsets are determined through X-ray photoelectron spectroscopy and optical bandgap measurements. A majority of these materials is identified as having a negative conduction-band offset with respect to Cu{sub 2}O; the detrimental impact of this on open-circuit voltage (V{sub OC}) is evaluated through 1-D device simulation. These results suggest that doping density of the n-type material is important as well, and that a poorly optimized heterojunction can easily mask changes in bulk minority carrier lifetime. Promising heterojunction candidates identified here include Zn(O,S) with [S]/[Zn] ratios >70%, and Ga{sub 2}O{sub 3}, which both demonstrate slightly positive conduction-band offsets and high V{sub OC} potential. This experimental protocol and modeling may be generalized to evaluate the efficiency potential of candidate heterojunction partners for other PV absorbers, and the materials identified herein may be promising for other absorbers with low electron affinities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Hydrogen reduction and metal-support interaction in a metastable metal-oxide system: Pd on rhombohedral In{sub 2}O{sub 3}

Highlights: • Metal-Support interaction in a metastable Pd/rh-In{sub 2}O{sub 3} material. • No influence of metal-support interaction on phase transformation rh-In{sub 2}O{sub 3}→c-In{sub 2}O{sub 3}. • Sequence of hydride, intermetallic compound formation and phase transformation. • High structural stability of reduced rh-In{sub 2}O{sub 3} and associated oxygen vacancies. • Metastable rh-In{sub 2}O{sub 3} more effective in initial intermetallic formation than c-In{sub 2}O{sub 3}. - Abstract: Structural and chemical consequences of reactive metal-support interaction (RMSI) effects occurring under hydrogen reduction in a metastable metal-oxide system have been exemplified for small PdO particles loaded onto rhombohedral In{sub 2}O{sub 3} (PdO/rh-In{sub 2}O{sub 3}) using synchrotron-based in situ X-ray diffraction experiments at temperatures up to 500 °C. rh-In{sub 2}O{sub 3} is a meta-stable In{sub 2}O{sub 3} polymorph that is prone to gas-phase dependent phase transformation to cubic In{sub 2}O{sub 3} (c-In{sub 2}O{sub 3}). Cross-influence of metal-support interaction and phase transformation can therefore be expected in similar temperature regimes. To separate both effects, comparable experiments have also been conducted on pure rh-In{sub 2}O{sub 3}. Phase transformation of pure rh-In{sub 2}O{sub 3} to cubic In{sub 2}O{sub 3} in hydrogen occurs between 415 °C and 450 °C. On Pd/rh-In{sub 2}O{sub 3}, a sequence of PdO reduction to Pd metal, followed by PdH{sub 0.706} hydride formation and subsequently, InPd and In{sub 3}Pd{sub 2} intermetallic compound formation have been observed between 30 °C and 500 °C. After the intermetallic compound formation is finished at around 400 °C, the phase transformation to c-In{sub 2}O{sub 3} sets in at exactly the same temperature as on pure rh-In{sub 2}O{sub 3} and extends over the same temperature range. This proves that the phase transformation of rh-In{sub 2}O{sub 3} to c-In{sub 2}O{sub 3} is not influenced by the reduction and the intermetallic compound formation. In contrast to Pd on c-In{sub 2}O{sub 3}, In-Pd compound formation from rh-In{sub 2}O{sub 3} occurs at much lower temperatures (230 °C vs. 300 °C), despite finally approaching the same compound stoichiometries (InPd and In{sub 3}Pd{sub 2}). This points to a high structural stability of reduced rh-In{sub 2}O{sub 3}/stability of oxygen vacancies (compared to c-In{sub 2}O{sub 3}) as well as to facilitated diffusion of reduced In(-O) species at low temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Metal–Oxide Interface Sites Created Using Atomic Layer Deposition and Tested for CO Oxidation

The performance of catalysts made out of Pt supported on TiO 2 thin films grown on SBA-15 (a silica mesoporous material) by atomic layer deposition (ALD) was characterized systematically by combining in situ infrared absorption spectroscopy (IR) with other techniques including electron microscopy and adsorption−desorption isothermal measurements. The titania films in the resulting high-surface-area catalysts were evenly distributed throughout the inner surface of the SBA-15 mesopores, and their thickness could be controlled at a submonolayer level, with 3 to 4 TiO 2 ALD cycles needed for the complete coverage of the silica sites. The titania films could be deposited either before or after adding the metal (Pt), which was dispersed in the form of small nanoparticles (NPs) approximately 4−6 nm in diameter, in order to exert some control on the density and nature of the Pt/TiO 2 interface sites. One important lesson deriving from this work is that such an order of deposition leads to significantly different catalysts in spite of the fact that most of their structural properties are similar. If the Pt is deposited on the titania films, the resulting metal NPs are slightly smaller than those grown on silica and display CO adsorption sites with lower surface Pt coordination numbers. On the other hand, when TiO 2 is deposited on the Pt/SBA-15 starting material, some titania grows on the metal and partially blocks its surface while also creating new interface sites where CO binds more weakly and displays lower C−O stretching frequencies. In terms of catalytic performance, the results from in situ IR CO site titration and kinetic measurements combined suggest a mechanism where CO first adsorbs on Pt atop sites and then migrates to Pt/TiO 2 interface sites, where oxidation takes place. Both types of sites appear to be similar in all the catalysts tested, but catalytic performance could be optimized by tuning their surface densities. Maximum catalytic activity was obtained when the TiO2 films were deposited first and with TiO 2 coverages of at least half a monolayer, that is, after at least 2 ALD cycles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗