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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Deliberately Designed Atomic-Level Silver-Containing Interface Results in Improved Rate Capability and Utilization of Silver Hollandite for Lithium-Ion Storage

α-MnO 2 -structured materials are generally classified as semiconductors, thus we present a strategy to increase electrochemical utilization through design of a conductive material interface. Surface treatment of silver hollandite (Ag x Mn 8 O 16 ) with Ag + (Ag 2 O) provides significant benefit to the resultant electrochemistry, including a decreased charge transfer resistance, and a 2-fold increase in deliverable energy density at high rate. The improved function of this designed interface relative to conventional electrode fabrication strategies is further highlighted.

25 ENERGY STORAGE↗
DOE OSTI2013

Co-Percolating Graphene-Wrapped Silver Nanowire Network for High Performance, Highly Stable, Transparent Conducting Electrodes

Transparent conducting electrodes (TCEs) require high transparency and low sheet resistance for applications in photovoltaics, photodetectors, flat panel displays, touch screen devices and imagers. Indium tin oxide (ITO), or other transparent conductive oxides, have typically been used, and provide a baseline sheet resistance (RS) vs. transparency (T) relationship. However, ITO is relatively expensive (due to limited abundance of Indium), brittle, unstable, and inflexible; moreover, ITO transparency drops rapidly for wavelengths above 1000 nm. Motivated by a need for transparent conductors with comparable (or better) RS at a given T, as well as flexible structures, several alternative material systems have been investigated. Single-layer graphene (SLG) or few-layer graphene provide sufficiently high transparency (≈97% per layer) to be a potential replacement for ITO. However, large-area synthesis approaches, including chemical vapor deposition (CVD), typically yield films with relatively high sheet resistance due to small grain sizes and high-resistance grain boundaries (HGBs). In this paper, we report a hybrid structure employing a CVD SLG film and a network of silver nanowires (AgNWs): RS as low as 22 Ω/ (stabilized to 13 Ω/ after 4 months) have been observed at high transparency (88% at λ = 550 nm) in hybrid structures employing relatively low-cost commercial graphene with a starting RS of 770 Ω/. This sheet resistance is superior to typical reported values for ITO, comparable to the best reported TCEs employing graphene and/or random nanowire networks, and the film properties exhibit impressive stability under mechanical pressure, mechanical bending and over time. The design is inspired by the theory of a co-percolating network where conduction bottlenecks of a 2D film (e.g., SLG, MoS2) are circumvented by a 1D network (e.g., AgNWs, CNTs) and vice versa. The development of these high-performance hybrid structures provides a route towards robust, scalable and low-cost approaches for realizing high-performance TCE.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Long-term Accumulation, Depth Distribution, and Speciation of Silver Nanoparticles in Biosolids-Amended Soils

Biosolids, when applied to soil, can be a source of metals and metal nanoparticles. One of the metals that forms nanoparticles is silver (Ag), which is commonly used in elemental (Ag(0)) form as an engineered nanomaterial in industrial or consumer products. The objective of this study was to quantify and characterize the accumulation and transport of Ag in a natural soil that has received agronomically-recommended rates of biosolids as fertilizer for the past 23 years (1994{2017). Total Ag concentrations were measured in biosolids and soil samples collected from 0 to 10 cm between 1996 and 2017. In addition, the depth distribution of Ag in the soil down to 60-cm depth was measured in 2017. Electron microscopy, in combination with X-ray spectroscopy, and X-ray absorption spectroscopy were used to identify the elemental association and oxidation state of the Ag in the samples. The Ag concentrations in the biosolids-amended soil increased steadily from 1996 until 2007, after which the concentrations leveled off at about 1.25 mg Ag kg-1 soil. This corresponded with a decrease of Ag concentrations in the biosolids over time. The majority of the Ag (82%) was confined to the top 10 cm of the soil, small amounts (14%) were detected in 10 to 20-cm depth, and trace amounts (4%) in 30 to 40-cm depth. The Ag in the biosolids and soil was identified as Ag-containing nanoparticles with a diameter of 10 to 12 nm. Ag was associated with S suggest that these 19 nanoparticles are Ag2S. This could be corroborated in biosolids with X-ray absorption spectroscopy (XANES); however, the Ag concentrations in the soil samples were too low to allow identification with XANES. Biosolids, when applied at agronomic rates in dryland cropping systems, represent an economically viable source of crop nutrients. In our study, long-term application of biosolids did not increase the concentration of total Ag in soil above a maximum of 1.5 mg Ag kg-1, and the Ag is present in the sulfide form. This concentration is below ecotoxicity limits for Ag2S in soil.

Taylor, Stephen E.↗
DOE OSTI2022

Mechanistic calculation of the effective silver diffusion coefficient in polycrystalline silicon carbide: Application to silver release in AGR-1 TRISO particles

The silicon carbide (SiC) layer in tristructural isotropic (TRISO) fuel particles serves as a barrier to prevent the escape of fission products produced and not retained in the fuel kernel. The release of silver (Ag) is a concern due to the long half-life of the 110m Ag isotope. However, accurately determining the fission gas release rate requires knowing the diffusion coefficient through the SiC layer. In this study, we leverage atomistic calculations of Ag diffusivity in SiC bulk and grain boundaries (GBs) to develop a mesoscale effective Ag diffusion coefficient (D eff ) in SiC. Since GBs serve as pathways for Ag diffusion, D eff is defined as a function of temperature and microstructure variables. In particular, the size of SiC grains in the direction perpendicular to diffusion is shown to significantly affect Ag diffusion. The prediction of the mechanistic, mesoscale approach falls within one order of magnitude of empirical values. The temperature and microstructure-dependent effective Ag diffusivity in SiC is implemented in the fuel performance code Bison with a correction factor to predict Ag release from AGR-1 TRISO fuel particles. We hereby quantify the impact of SiC grain size on Ag release and improve Bison’s predictions.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Atomic Scale Account of the Surface Effect on Ionic Transport in Silver Hollandite

Here, nanosized electrodes for Li-ion batteries typically display improved electrochemical properties, which are generally attributed to the reduced dimensionality for lithiation. However, the intriguing roles of surface defects and disorder associated with the nanosized materials are often overlooked. Here, combining atomically resolved structural analysis with density functional theory calculations, we reveal that the formation of intrinsic oxygen vacancies near surface in silver hollandite nanorods modifies the local atomic structure and valence state. These surface reconstructions resulted from oxygen vacancies can significantly affect the diffusion pathways in what are otherwise one-dimensional (1D) tunneled structures. On the basis of energy barrier calculations, we demonstrate that the oxygen vacancies boost ionic transport through the edge sharing MnO 6 polyhedra in the a–b plane. Thus, within a single rod different from the inherent 1D tunnel diffusion in the interior, the ionic transport at oxygen vacancy decorated surfaces likely adopts a three-dimensional diffusion pathway including both tunnel and planar diffusion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Silver Sulfide and Silver Sulfate as Aging Byproducts and Adsorbents for Gaseous Iodine Capture in Spent Nuclear Fuel Reprocessing

While it is considered a promising adsorbent for radioiodine capture in spent nuclear fuel reprocessing off-gas, silver functionalized silica aerogel (Ag 0 -aerogel) experiences a capacity loss when exposed to other off-gas components (O 2 , H 2 O, NO, and NO 2 ) through a process known as aging. Ag 2 S and Ag 2 SO 4 were identified as major byproducts of aging, but their impact on iodine adsorption remains unclear. Thus, to further investigate aging, we loaded Ag 2 S and Ag 2 SO 4 powders with molecular iodine (I 2 ) at 150 °C and characterized their properties. The I 2 adsorption capacity of Ag 2 SO 4 was 0.12 wt % after 72 h, suggesting its formation directly reduces the capacity of the Ag 0 -aerogel. Conversely, Ag 2 S had an iodine capacity of 86.8 wt % and near total Ag utilization after 240 h. Given its high capacity and availability, we evaluated the feasibility of Ag 2 S as an I 2 adsorbent in future applications. Finally, several drawbacks need to be overcome, including the relatively slow uptake rate, potential emission of another hazardous byproduct (SO 2 ), and potential aging effects (e.g., Ag 2 S conversion to Ag 2 SO 4 ) before Ag 2 S can be applied for the radioiodine capture process.

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

Validation of Methods for Computational Catalyst Design: Geometries, Structures, and Energies of Neutral and Charged Silver Clusters

We report a systematic study of small silver clusters, Agn, Agn+, and Agn–, n = 1–7. We studied all possible isomers of clusters with n = 5–7. We tested 42 exchange–correlation functionals, and we assess these functionals for their accuracy in three respects: geometries (quantitative prediction of internuclear distances), structures (the nature of the lowest-energy structure, for example, whether it is planar or nonplanar), and energies. We find that the ingredients of exchange–correlation functionals are indicators of their success in predicting geometries and structures: local exchange–correlation functionals are generally better than hybrid functionals for geometries; functionals depending on kinetic energy density are the best for predicting the lowest-energy isomer correctly, especially for predicting two-dimensional to three-dimenstional transitions correctly. The accuracy for energies is less sensitive to the ingredient list. Our findings could be useful for guiding the selection of methods for computational catalyst design.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Space- and time-resolved small angle X-ray scattering to probe assembly of silver nanocrystal superlattices

Abstract The structure of nanocrystal superlattices has been extensively studied and well documented, however, their assembly process is poorly understood. In this work, we demonstrate an in situ space- and time-resolved small angle X-ray scattering measurement that we use to probe the assembly of silver nanocrystal superlattices driven by electric fields. The electric field creates a nanocrystal flux to the surface, providing a systematic means to vary the nanocrystal concentration near the electrode and thereby to initiate nucleation and growth of superlattices in several minutes. Using this approach, we measure the space- and time-resolved concentration and polydispersity gradients during deposition and show how they affect the superlattice constant and degree of order. We find that the field induces a size-selection effect that can reduce the polydispersity near the substrate by 21% leading to better quality crystals and resulting in field strength-dependent superlattice lattice constants.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Weak competing interactions control assembly of strongly bonded TCNQ ionic acceptor molecules on silver surfaces

The energy scales of interactions that control molecular adsorption and assembly on surfaces can vary by several orders of magnitude, yet the importance of each contributing interaction is not apparent a priori. Tetracyanoquinodimethane (TCNQ) is an archetypal electron acceptor molecule and it is a key component of organic metals. On metal surfaces, this molecule also acts as an electron acceptor, producing negatively charged adsorbates. It is therefore rather intriguing to observe attractive molecular interactions in this system that were reported previously for copper and silver surfaces. In this paper, our experiments compared TCNQ adsorption on noble metal surfaces of Ag(100) and Ag(111). In both cases we found net attractive interactions down to the lowest coverage. However, the morphology of the assemblies was strikingly different, with two-dimensional islands on Ag(100) and one-dimensional chains on Ag(111) surfaces. This observation suggests that the registry effect governed by the molecular interaction with the underlying lattice potential is critical in determining the dimensionality of the molecular assembly. Using first-principles density functional calculations with a van der Waals correction scheme, we revealed that the strengths of major interactions (i.e., lattice potential corrugation, intermolecular attraction, and charge-transfer-induced repulsion) are all similar in energy. The van der Waals interactions, in particular, almost double the strength of attractive interactions, making the intermolecular potential comparable in strength to the diffusion potential and promoting self-assembly. However, it is the anisotropy of local intermolecular interactions that is primarily responsible for the difference in the topology of the molecular islands on Ag(100) and Ag(111) surfaces. Finally, we anticipate that the intermolecular potential will become more attractive and dominant over the diffusion potential with increasing molecular size, providing new design strategies for the structure and charge transfer within molecular layers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Epitaxial Electrodeposition of Wide Bandgap Cuprous Bromide on Silver via a Silver Bromide Buffer Layer

Cuprous halides are an important class of wide bandgap p-type semiconductors used in opto-electronics. Cuprous bromide (CuBr) shows potential for short-wavelength devices due to a large exciton binding energy (108 meV) and near-ultraviolet bandgap (3.1 eV). However, the growth of high-quality epitaxial CuBr films by electrodeposition has remained a challenge. Here, we introduce a low-cost electrochemical procedure for producing epitaxial CuBr(111) on a Ag(111) substrate by a [111]-oriented silver bromide (AgBr) buffer layer. The AgBr buffer layer forms during the electrodeposition of the CuBr. The mismatch between CuBr(111) and AgBr(111) is –1.3%. A plausible mechanism for nucleation and growth of the epitaxial CuBr is proposed. X-ray techniques including high resolution X-ray diffraction and X-ray pole figures are used to determine the epitaxial relationship. CuBr(100) is also produced on a Ag(100) surface by a AgBr(100) buffer layer that is rotated in-plane 45° relative to the Ag(100) surface. In conclusion, this in-plane rotation reduces the lattice mismatch from +39.5% for an unrotated film to –1.4% for a 45° rotated film.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗