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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Mitigation of Silver Ion Loss from Solution by Polymer Coating of Metal Surfaces

Spacecraft potable water systems require a biocidal agent that effectively provides both immediate and residual disinfection over long periods of time. Ionic silver (Ag+) is a leading candidate for this application, but suffers from rapid concentration loss due interactions with the metal storage containers and tubing. In order to maintain biocidal efficacy in systems with long periods of dormancy and to reduce the required rate of Ag+ injection, it is necessary to develop alternative materials and coatings for certified metal alloys that significantly reduce the Ag+ loss. In this work, we investigate the performance of two unusual polymers, Teflon AF 2400 and parylene-AF4, as barrier coatings under immersion in 400 ppb Ag+. We show that 25 m-thick parylene-AF4 is a promising coating with Ag+ losses similar to PTFE. Key challenges with this material include maintenance of adhesion under long-term immersion and control of deposition during the internal coating of high-aspect ratio tubing. Solutions to these problems may including surface structuring of substrates for mechanical anchoring or an alternative parylene-C chemistry (with more stable adhesion), and dynamic spatio-temporal control of substrate temperature, respectively.

water↗
NASA NTRSDate not supplied

Mitigation of Silver Ion Loss from Solution by Polymer Coating of Metal Surfaces, Part IV

Ionic silver (Ag+) biocide is a leading candidate to provide residual microbial control in spacecraft potable water systems, but suffers from rapid concentration loss due to interactions with the metallic storage containers and tubing. One approach to resolve this problem is the coating of metal surfaces with an inert barrier film. In previous reports, we have described our investigations addressing Ag+ loss mitigation and adhesion performance of parylene barrier coatings on coupons of several metal alloys and 316Ltubing under static immersion. In such conditions, parylene-C and -AF4 coatings have shown excellent Ag+loss mitigation and mixed long-term adhesion performance, depending on parylene species and substrate surface chemistry/structure. In Part IV of this series, we report on our work to investigate the performance of parylene-C barrier coatings, under more challenging and realistic conditions, in order to evaluate potential suitability for use. The resilience and associated Ag+ loss with Parylene-C coating on½” (12.7 mm)316L tubing and fittings under medium-term immersion and repeated fitting dis/reassembly were investigated. Potential mechanical challenges to barrier coatings in spacecraft potable water systems were investigated, with two main focuses being identified: liquid flow/pressure cycling in tubing and cyclic operation of bellows in positive-expulsion storage tanks. Two corresponding testbeds for experimental characterization of coating performance were developed. In the Flow/Pressure Testbed System, Ag+ solution will be pumped through internally coated 316L tubing, with optional pressure cycling. In the Bellows Tank Testbed System, an internally coated edge-welded 316L bellows containing Ag+ solution will be cyclically extended and compressed, analogous to the operation of bellows tanks used for potable water storage and delivery on the International Space Station. The design and operation of these testbeds are described. Finally, the Ag+ adsorption and saturation behaviors of Kalrez and Viton, for potential use as seal materials in fittings and other connections, were characterized in limited experiments.

mitigation↗
DOE OSTI2024

Ligand‐Mediated Quantum Yield Enhancement in 1‐D Silver Organothiolate Metal–Organic Chalcogenolates

X-ray free electron laser (XFEL) microcrystallography and synchrotron single-crystal crystallography are used to evaluate the role of organic substituent position on the optoelectronic properties of metal–organic chalcogenolates (MOChas). MOChas are crystalline 1D and 2D semiconducting hybrid materials that have varying optoelectronic properties depending on composition, topology, and structure. While MOChas have attracted much interest, small crystal sizes impede routine crystal structure determination. A series of constitutional isomers where the aryl thiol is functionalized by either methoxy or methyl ester are solved by small molecule serial femtosecond X-ray crystallography (smSFX) and single crystal rotational crystallography. While all the methoxy examples have a low quantum yield (0-1%), the methyl ester in the ortho position yields a high quantum yield of 22%. Here, the proximity of the oxygen atoms to the silver inorganic core correlates to a considerable enhancement of quantum yield. Four crystal structures are solved at a resolution range of 0.8–1.0 Å revealing a collapse of the 2D topology for functional groups in the 2- and 3- positions, resulting in needle-like crystals. Further analysis using density functional theory (DFT) and many-body perturbation theory (MBPT) enables the exploration of complex excitonic phenomena within easily prepared material systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Hidden Local Symmetry Breaking in Silver Diamondoid Compounds is Root Cause of Ultralow Thermal Conductivity

Typically, conventional structure transitions occur from a low symmetry state to a higher symmetry state upon warming. In this work, an unexpected local symmetry breaking in the tetragonal diamondoid compound AgGaTe 2 is reported, which, upon warming, evolves continuously from an undistorted ground state to a locally distorted state while retaining average crystallographic symmetry. This is a rare phenomenon previously referred to as emphanisis. This distorted state, caused by the weak sd 3 orbital hybridization of tetrahedral Ag atoms, causes their displacement off the tetrahedron center and promotes a global distortion of the crystal structure resulting in strong acoustic–optical phonon scattering and an ultralow lattice thermal conductivity of 0.26 W m –1 K –1 at 850 K in AgGaTe 2 . Here, the findings explain the underlying reason for the unexpectedly low thermal conductivities of silver-based compounds compared to copper-based analogs and provide a guideline to suppressing heat transport in diamondoid and other materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Excitonic Anisotropy in Single‐Crystalline 2D Silver Phenylchalcogenides

2D materials exhibiting in‐plane anisotropy enable new applications in directional energy transport and polarized optical response. Silver phenylchalcogenides (AgEPh) – including mithrene (AgSePh), tethrene (AgTePh), and thiorene (AgSPh) – represent an exciting new addition to this family, with optical response spanning the visible to near‐UV. Here, excitonic anisotropy is predicted and characterized in this family of materials using a combination of ab initio theory and optical micro‐spectroscopy of single‐crystalline flakes. Using density functional theory and GW with the Bethe–Salpeter equation calculations, it is revealed that all AgEPh compounds exhibit anisotropic electronic band structure and host multiple delocalized excitons with in‐plane anisotropy. Room‐temperature polarization‐resolved optical micro‐spectroscopy shows that orthogonally polarized excitons with similar energy lead to nearly isotropic absorption in AgSPh, whereas energy separation between excitonic resonances in AgSePh and AgTePh leads to strong absorption and emission anisotropy. Cryogenic reflectance micro‐spectroscopy further reveals exciton fine structure in AgSePh, reconciling the discrepancies between room‐temperature experiments and theoretical predictions. Finally, it is demonstrated that the optical response of thicker AgEPh crystals is influenced by photonic effects arising from finite crystal size. Overall, this work advances the understanding of the relationship between anisotropic structure, composition, and excitonic properties in AgEPh, providing a foundation for technological integration.

2D↗
DOE OSTI2023

Atomically Dispersed Silver Atoms Embedded in NiCo Layer Double Hydroxide Boost Oxygen Evolution Reaction

Abstract Bimetallic layered double hydroxides (LDHs) are promising catalysts for anodic oxygen evolution reaction (OER) in alkaline media. Despite good stability, NiCo LDH displays an unsatisfactory OER activity relative to the most robust NiFe LDH and CoFe LDH. Herein, a novel NiCo LDH electrocatalyst modified with single‐atom silver grown on carbon cloth (Ag SA ‐NiCo LDH/CC) that exhibits exceptional OER activity and stability in 1.0 m KOH is reported. The Ag SA ‐NiCo LDH/CC catalyst only requires a low overpotential of 192 mV to reach a current density of 10 mA cm −2 , obviously boosting the OER activity of NiCo LDH/CC (410 mV@10 mA cm −2 ). Inspiringly, Ag SA ‐NiCo LDH/CC can maintain its high activity for up to 500 h at a large current density of 100 mA cm −2 , exceeding most single‐atom OER catalysts. In situ Raman spectroscopy studies uncover that the in situ formed NiCoOOH during OER is the real active species. Hard X‐ray absorption spectrum (XAS) and density functional theory (DFT) calculations validate that single‐atom Ag occupying Ni site increases the chemical valence of Ni elements, and then weakens the adsorption of oxygen‐contained intermediates on Ni sites, fundamentally accounting for the enhanced OER performance.

Chemistry↗
DOE OSTI2024

Nanocompression of 20 nm Silver Nanoparticles: In situ Aberration‐Corrected TEM and Atomistic Simulations

Single‐crystalline nanoparticles play an increasingly important role in a wide variety of fields including pharmaceuticals, advanced materials, catalysts for fuel cells, energy materials, as well as environmental detection and monitoring. Yet, the deformation mechanisms of very small nanoparticles are still poorly understood, in particular the role played by single dislocations and their interaction with surfaces. Here, in this work, silver nanoparticles with particularly small dimensions (≈20 nanometers in diameter) are compressed in situ in an aberration‐corrected transmission electron microscopy (TEM) and molecular dynamics (MD) simulations. During compression, the emergence of both dislocations and nanotwins are observed. However, these defects prove to be unstable and disappear upon removal of the indenter. Atomistic simulations confirm the role played by image stresses associated with the nearby surfaces and the reduction in dislocation line length as it approaches the free surface, thereby supporting the experimental observations. These results provide justification for the frequent observation of the absence of dislocations in nanoparticles of a few nanometers in size during in situ experiments, even after significant deformation. This phenomenon contributes to the self‐healing of samples through dislocation ejection toward the surfaces.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Laser‐Sintered Silver Metallization for Silicon Heterojunction Photovoltaic Cells

Herein, a novel metallization technique is reported for crystalline silicon heterojunction (SHJ) solar cells in which silver (Ag) fingers are printed on the SHJ substrates by dispensing Ag nanoparticle‐based inks through a needle and then sintered with a continuous‐wave carbon dioxide (CO 2 ) laser. The impact of the Ag ink viscosity on the line quality and the line resistance is investigated on three Ag inks with different viscosities. Increasing ink viscosity yields higher Ag contact heights, larger aspect ratios, and lower line resistance values. The Ag line height increases from less than a micrometer to ≈18.62 ± 3.48 μm with the increasing viscosity. Photoluminescence imaging shows that the low‐resistance Ag metal contacts obtained do not result in any passivation damage of the SHJ substrate. This is because the wavelength of light emitted from the CO 2 laser (i.e., 10.6 μm) leads to optical absorption in the Ag, but this light is effectively transparent to the transparent conductive oxide film, amorphous silicon films, and crystalline silicon substrate. Bulk resistivity values as low as 6.5 μΩ cm are obtained for the laser‐sintered Ag contact and printed using the Ag ink with the highest viscosity in this work.

Mousumi, Jannatul Ferdous↗
DOE OSTI2022

Elucidating the temperature and density dependence of silver chloride hydration numbers in high-temperature water vapor: A first-principles molecular simulation study

Hydration numbers of metal complexes in low-density aqueous solutions are required for developing geochemical models for ore-forming metals and for designing supercritical desalination processes. In this study, we investigate the temperature and density dependence of the hydration numbers of silver chloride at 623 K, 673 K, and 713 K and densities of 10–100 kg/m 3 . Experimental estimates of the hydration number in the literature for AgCl at these conditions are inconclusive and possibly contradictory as to the temperature and density dependence. First-principles molecular simulation presents an attractive alternative to experimental measurements. Specifically, recent work shows that machine-learning-accelerated nested Monte Carlo simulations provide reliable estimates for the hydration numbers of CuCl at 623 K from 10 to 100 kg/m 3 . Using the same technique, we find a monotonic temperature dependence, with the hydration number decreasing slightly with increasing temperature. In addition, the simulation-predicted hydration numbers steadily increase with increasing density. These temperature and density trends are in agreement with certain experimental data sets. Therefore, this work demonstrates how first-principles Monte Carlo simulations assist in resolving discrepancies between experimental data sets. Our simulation results also correctly predict that the hydration number, and thus also the solubility, of AgCl is lower than that of CuCl under the same conditions. Furthermore, the bond length and angle formed between the water complex and AgCl differ from those for CuCl, consistent with the lower solubility of AgCl.

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

Crosslinked polymeric ionic liquid stationary phases incorporating a combination of silver(I) and copper(II) ions for olefin separations by gas chromatography

The development of efficient and selective olefin separation technologies is a critical challenge within the chemical industry given the high energy demands of conventional cryogenic distillation methods. To address this, the study explores the effectiveness of polymeric ionic liquid (PIL) stationary phases in gas chromatography (GC) that incorporate both silver(I) ([Ag + ]) and copper(II) ([Cu 2+ ]) ions for enhanced olefin separation via π-complexation interactions. Further, the effects of both non-crosslinked and crosslinked PIL stationary phases containing varying ratios of [Ag⁺] and [Cu²⁺] ions were systematically investigated to evaluate their impact on the separation of olefins from paraffins and structurally similar olefins. Retention measurements using a broad range of olefinic probes revealed that [Ag⁺] ions provided stronger and more consistent π-complexation in PIL-based stationary phases, while [Cu²⁺] ions preferentially enhance olefin retention in crosslinked systems. Furthermore, thermal stability studies showed that [Ag + ]-containing PIL stationary phases maintain stable olefin separation efficiency over prolonged exposure under elevated temperatures, while crosslinked PIL stationary phases containing [Cu 2+ ] ions exhibited stronger retention due to increased surface adsorption. These findings provide insight into the tunability of metal–olefin interactions using PIL-based stationary phases and suggest design strategies for achieving thermally stable and highly selective chromatographic separations of unsaturated hydrocarbons.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Evaluating the effect of ionomer chemical composition in silver-ionomer catalyst inks toward the oxygen evolution reaction by half-cell measurements and water electrolysis

The effect of anion exchange ionomer (AEI) chemistry on the kinetics of the oxygen evolution reaction (OER) was systematically studied in both half-cell and single-cell electrolysis experiments. OER was studied in 1 M K 2 CO 3 at 50°C using an array of ionomer-silver catalyst inks deposited on Ni foam. Different ionomer modifications were investigated to optimize the OER performance. The AEI used in this work features a block copolymer backbone of polychloromethylstyrene-b-polycyclooctene-b-polychloromethylstyrene which was functionalized with either benzyltrimethylammonium (TMA) or benzylmethylpiperidinium (MPRD) quaternary ammonium cations. Here, using an MPRD quaternary ammonium cation shifted the rate determining step at high overpotentials, ultimately providing enhanced performance. Increasing the catalyst ink dilution was also found to substantially improve mass activity and catalyst utilization (increase from 35 to 88 A g –1 Ag), likely by reducing the ionomer thickness and decreasing transport resistances. In the final ionomer modification, the Ni foam substrate was leveraged to partially hydrogenate the polycyclooctene midblock to be polyethylene-like at the Ni interface. A significant increase in the electrochemical surface area (Cdl increased from 8.8 to 20.8 mF cm –2 ) and performance (by 47 mA cm –2 or 29 A g –1 Ag) was observed with the incorporation of polyethylene. Kinetic results from half-cell experiments were validated via single-cell anion exchange membrane electrolysis experiments, where the optimized electrode displayed enhanced performance in both 1 M K 2 CO 3 and DI H 2 O.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗