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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
DOE OSTI2021

Nanoparticle Superlattices through Template-Encoded DNA Dendrimers

The chemical interactions that lead to the emergence of hierarchical structures are often highly complex and difficult to program. In this paper, the synthesis of a series of superlattices based upon 30 different structurally reconfigurable DNA dendrimers is reported, each of which presents a well-defined number of single-stranded oligonucleotides (i.e., sticky ends) on its surface. Such building blocks assemble with complementary DNA-functionalized gold nanoparticles (AuNPs) to yield five distinct crystal structures, depending upon choice of dendrimer and defined by phase symmetry. These DNA dendrimers can associate to form micelle-dendrimers, whereby the extent of association can be modulated based upon surfactant concentration and dendrimer length to produce a low-symmetry Ti5Ga4-type phase that has yet to be reported in the field of colloidal crystal engineering. Taken together, colloidal crystals that feature three different types of particle bonding interactions.template-dendron, dendrimer-dendrimer, and DNA-modified AuNP-dendrimer.are reported, illustrating how sequence-defined recognition and dynamic association can be combined to yield complex hierarchical materials.

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

Nonprecious Single Atom Catalyst for Methane Pyrolysis

The development of a suitable catalytic system for methane pyrolysis reactions requires a detailed investigation of the activation energy of C-H bonds on catalysts, as well as their stability against sintering and coke formation. In this work, both single-metal Ni atoms and small clusters of Ni atoms deposited on titanium nitride (TiN) plasmonic nanoparticles were characterized for the C-H bond activation of a methane pyrolysis reaction using ab initio spin-polarized density functional theory (DFT) calculations. The present work shows the complete reaction pathway, including energy barriers for C-H bond activation and dehydrogenated fragments, during the methane pyrolysis reaction on catalytic systems. Interestingly, the C-H bond activation barriers were low for both Ni single-atom and Ni-clusters, showing the energy barriers of ~1.10 eV and ~0.88 eV, respectively. Additionally, single-atom Ni-TiN showed weaker binding to adsorbates, and a net endothermic reaction pathway indicated that the single-atom Ni-TiN was expected to resist coke formation on its surface. However, these Ni single-atom catalysts can sinter, aggregate into a small cluster, and form a coke layer from the highly exothermic reaction pathway that the cluster takes despite the facile reaction pathway.

08 HYDROGEN↗
DOE OSTI2021

Ligand-coordinated Ir single-atom catalysts stabilized on oxide supports for ethylene hydrogenation and their evolution under a reductive atmosphere

In this work, we present a novel series of oxide-supported Ir-ligand single-atom catalysts (SACs) for ethylene hydrogenation. The SACs were created by a metal–ligand self-assembly strategy developed by our group, using one of two ligands, either 1,10-phenanthroline-5,6-dione (PDO) or 3,6-Di-2-pyridyl-1,2,4,5-tetrazine (DPTZ), on powder supports of either CeO 2 or MgO. Characterization by XAS, XPS, and CO adsorption proved that Ir exist principally as highly uniform, cationic single-atoms. Ir SACs show significantly higher durability and metal utilization efficiency than Ir nanoparticle (NP) catalysts during ethylene hydrogenation at 100 °C, as well as excellent stability, as no Ir aggregates were detected after >10 h reaction. The activity can be tuned by ligand and support effects: PDO and CeO 2 are superior to DPTZ and MgO, respectively. This tunability is attributed to differences in H 2 activation capability, which results from differences in support reducibility, electron density on Ir, and, potentially, the local coordination environment of Ir. The Ir SACs lose H 2 activation activity either under inert gas or under H 2 . Through XPS and in situ XAS studies, we attributed the former to the reversible loss of Ir hydride, which is the active species for H 2 activation, and the latter to irreversible over-hydrogenation and loss of Ir–O/N coordination. This work presents a new type of Ir hydrogenation SACs that are more durable, efficient, and tunable than supported Ir NPs, while more stable than homogeneous Ir complexes. It also offers fundamental understanding regarding ligand and support effects, as well as the evolution of Ir single-atoms under H 2 , instructing future design of stable, effective hydrogenation SACs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Toward efficient single-atom catalysts for renewable fuels and chemicals production from biomass and CO 2

Transformation of biomass and CO 2 into renewable value-added chemicals and fuels has been identified as a promising strategy to fulfill high energy demands, lower greenhouse gas emissions, and exploit under-utilized resources. Cost-effective and performance-efficient catalysts are of great importance to lowering the conversion cost of biomass and CO 2 . Significant progress has been made to advance the catalyst design for these processes, with metal catalysts playing a critical role in many involved catalytic reactions. Traditional nanoparticle-based metal catalysts still require improvement in metal utilization rates, stability, and selectivity tunability. Single-atom catalysts, which have maximum atomic efficiency and a uniform and tunable metal center, as well as an adjustable metal-support interaction, provide potential opportunities to boost catalyst efficiency and thermal stability. Their well-defined and uniform structure also provides advantages to fundamental studies for understanding of the intrinsic reaction mechanism and site requirement in biomass and CO 2 conversion. In this article, we summarize and highlight the recent advances in converting biomass and CO 2 to renewable fuels and chemicals using single-atom catalysts. We discuss the design principles of single-atom catalysts and their potential applications to biomass and CO 2 upgrading as well as the origins of catalytic activity. Moreover, we compare the catalytic efficiency of various catalysts reported thus to provide a fair assessment of these catalysts. Finally, perspectives are given on the interesting fields that may guide future studies.

09 BIOMASS FUELS↗
DOE OSTI2020

Plasmon excitations in chemically heterogeneous nanoarrays

The capability of collective excitations, such as localized surface plasmon resonances, to produce a versatile spectrum of optical phenomena is governed by the interactions within the collective and single-particle responses in the finite system. In many practical instances, plasmonic metallic nanoparticles and arrays are either topologically or chemically heterogeneous, which affects both the constituent transitions and their interactions. Here, the formation of collective excitations in weakly Cu- and Pd-doped Au nanoarrays is described using time-dependent density functional theory. The additional impurity-induced modes in the optical response can be thought to result from intricate interactions between separated excitations or transitions. In this work, we investigate the heterogeneity at the impurity level, the symmetry aspects related to the impurity position, and the influence of the impurity position on the confinement phenomena. The chemically rich and symmetry-dependent quantum mechanical effects are analyzed with transition contribution maps demonstrating the possibility to develop nanostructures with more controlled collective properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Sample Preparation and Experimental Design for In Situ Multi-Beam Transmission Electron Microscopy Irradiation Experiments

We discuss the need to understand materials exposed to overlapping extreme environments such as high temperature, radiation, or mechanical stress. When these stressors are combined there may be synergistic effects that enable unique microstructural evolution mechanisms to activate. Understanding of these mechanisms is necessary for the input and refinement of predictive models and critical for engineering of next generation materials. The basic physics and underlying mechanisms require advanced tools to be investigated. The in situ ion irradiation transmission electron microscope (I 3 TEM) is designed to explore these principles. To quantitatively probe the complex dynamic interactions in materials, careful preparation of samples and consideration of experimental design is required. Particular handling or preparation of samples can easily introduce damage or features that obfuscate the measurements. There is no one correct way to prepare a sample; however, many mistakes can be made. The most common errors and things to consider are highlighted within. The I 3 TEM has many adjustable variables and a large potential experimental space, therefore it is best to design experiments with a specific scientific question or questions in mind. Experiments have been performed on large number of sample geometries, material classes, and with many irradiation conditions. The following are a subset of examples that demonstrate unique in situ capabilities utilizing the I 3 TEM. Au nanoparticles prepared by drop casting have been used to investigate the effects of single ion strikes. Au thin films have been used in studies on the effects of multibeam irradiation on microstructure evolution. Zr films have been exposed to irradiation and mechanical tension to examine creep. Ag nanopillars were subjected to simultaneous high temperature, mechanical compression, and ion irradiation to study irradiation induced creep as well. These results impact fields including: structural materials, nuclear energy, energy storage, catalysis, and microelectronics in space environments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Size- and concentration-dependent Eu 2+ /Eu 3+ mixed luminescent characteristics of rare-earth-doped CaF 2 nanoparticles and their monolithic epoxy nanocomposites

CaF 2 is a promising luminescent host material for a wide range of applications, due to its high transparency, non-hygroscopy, low refractive index, low density, low backscattering efficiency, and abundance in nature. Here we report the photoluminescence (PL) and cathodoluminescence (CL) characteristics of rare-earth-doped CaF 2 nanoparticles and their composite monoliths with epoxy with visible emissions. The CaF 2 nanoparticles of ca. 36, 108 and 305 nm were prepared by a facile solution-mixing process and subsequent hydrothermal treatment. As the particle size decreases, the luminescence intensity increases for single-doped particles, while oppositely decreases for codoped particles because of energy transfer. Further, Eu 2+ - and Tb 3+ -codoped CaF 2 nanoparticles exhibit red emission, providing an efficient path for red emission through an energy transfer by Tb 3+ bridging without direct Eu 3+ doping. The effects of size and concentration are found to be pronounced in CL than PL, as the charge transfer between Eu 2+ and Eu 3+ reduces the concentration quenching in CL. The luminescence emission characteristics of epoxy/CaF 2 monoliths are different from those of particles due to the interactions with the epoxy molecules, and thus the energy transfer is hindered in PL while not in CL, enabling them for high-energy irradiation applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Plasmon assisted synthesis of TiN-supported single-atom nickel catalysts

We report the deposition of single atom nickel catalyst on refractory plasmonic titanium nitride (TiN) nanomaterials supports using the wet synthesis method under visible light irradiation. TiN nanoparticles efficiently absorb visible light to generate photoexcited electrons and holes. Photoexcited electrons reduce nickel precursor to deposit Ni atoms on TiN nanoparticles’ surface. The generated hot holes are scavenged by the methanol. We studied the Ni deposition on TiN nanoparticles by varying light intensity, light exposure time, and metal precursor concentration. These studies confirmed the photodeposition method is driven by hot electrons and helped us to find optimum synthesis conditions for single atoms deposition. We characterized the nanocatalysts using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We used density functional theory (DFT) calculations to predict favorable deposition sites and aggregation energy of Ni atoms on TiN. Surface defect sites of TiN are most favorable for single nickel atoms depositions. Interestingly, the oxygen sites on native surface oxide layer of TiN also exhibit strong binding with the single Ni atoms. Plasmon enhanced synthesis method can facilitate photodeposition of single atom catalysts on a wide class of metallic supports with plasmonic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

MoS 2 -supported Au 31 for CO hydrogenation: A first-principle study

While the basal plane of single-layer molybdenum disulphide (MoS 2 ) is inert, attempts have been made to functionalize it chemically through the creation of defects and/or addition of dopants. With nanoparticles as dopants, the authors present density functional theory-based calculations of the hydrogenation of CO on a 31-atom, bilayer Au cluster supported on single-layer MoS 2 (Au31/MoS 2 ). Not surprisingly, the adsorption and reaction of all species involved in the hydrogenation occur at the edges of the cluster—the regions at which the interaction between MoS 2 and the Au cluster is tracked to be the strongest. The authors find two possible mechanisms that lead to the formation of methanol: (1) CO* → CHO* → CH 2 O* → CH 3 O* → CH 3 OH* and (2) CO* → CHO* → HCOH* → CH2OH* → CH3OH*, where * indicates the adsorbed species. Detailed analysis of the reaction pathways, however, does not result in favoring one mechanism over the other. Rather, both mechanisms are facile. In addition, the rate-limiting step in each mechanism is found to be the formation of the formyl radical group (CO* + H* → CHO*).

2D materials↗
DOE OSTI2024

Dynamic Copper Site Redispersion through Atom Trapping in Zeolite Defects

Single-site copper-based catalysts have shown remarkable activity and selectivity for a variety of reactions. However, deactivation by sintering in high-temperature reducing environments remains a challenge and often limits their use due to irreversible structural changes to the catalyst. Here, we report zeolite-based copper catalysts in which copper oxide agglomerates formed after reaction can be repeatedly redispersed back to single sites using an oxidative treatment in air at 550 °C. Under different environments, single-site copper in Cu–Zn–Y/deAlBeta undergoes dynamic changes in structure and oxidation state that can be tuned to promote the formation of key active sites while minimizing deactivation through Cu sintering. For example, single-site Cu 2+ reduces to Cu 1+ after catalyst pretreatment (270 °C, 101 kPa H 2 ) and further to Cu0 nanoparticles under reaction conditions (270–350 °C, 7 kPa EtOH, 94 kPa H 2 ) or accelerated aging (400–450 °C, 101 kPa H 2 ). After regeneration at 550 °C in air, agglomerated CuO was dispersed back to single sites in the presence and absence of Zn and Y, which was verified by imaging, in situ spectroscopy, and catalytic rate measurements. Ab initio molecular dynamics simulations show that solvation of CuO monomers by water facilitates their transport through the zeolite pore, and condensation of the CuO monomer with a fully protonated silanol nest entraps copper and reforms the single-site structure. Importantly, the capability of silanol nests to trap and stabilize copper single sites under oxidizing conditions could extend the use of single-site copper catalysts to a wider variety of reactions and allows for a simple regeneration strategy for copper single-site catalysts.

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

In situ temperature synthesis and characterization of ferroelectric PZN-4.5PT nanoparticles’ thin films using synchrotron light source

Despite the excellent properties of Pb(Zn 1/3 Nb 2/3 )O 3 -4.5PbTiO 3 (PZN-4.5PT) single crystals, the greatest difficulty for their application on electronic devices is to make them to thin layers related to the difficulty to make them as ceramic materials. In this paper, we use the combined USAXS/SAXS/WAXS instrument at 9ID beamline at APS-ANL for in situ characterization of PZN-4.5PT inorganic perovskite nanoparticles thin films deposited on nanotextured silicon to understand the phase transitions and determine the observed microcrystals' structure. Here, the sample was annealed from ambient to 1000°C. The results revealed structure changes in the nanoparticles' thin films which could be explained by the new phase that can be assigned to the Pb 3 (PO 4 )2-based component. The peak at 31° indicates the presence of the rhombohedral phase perovskites assigned to the nanoparticles. WAXS characterization permitted to identification of many transitions during thermal annealing like dehydration or dihydroxylation of phosphorus gel -OH bonds and internal water.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of Solvent Composition on Non-DLVO Forces and Oriented Attachment of Zinc Oxide Nanoparticles

Oriented attachment (OA) occurs when nanoparticles in solution align their crystallographic axes prior to colliding and subsequently fuse into single crystals. Traditional colloidal theories such as DLVO provide a framework for evaluating OA but fail to capture key particle interactions due to the atomistic details of both the crystal structure and the interfacial solution structure. Using zinc oxide as a model system, we investigated the effect of the solvent on short-ranged and long-ranged particle interactions and the resulting OA mechanism. In situ TEM imaging showed that ZnO nanocrystals in toluene undergo long-range attraction comparable to 1kT at separations of 10 nm and 3kT near particle contact. These observations were rationalized by considering non-DLVO interactions, namely dipole-dipole forces and torques between the polar ZnO nanocrystals. Langevin dynamics simulations showed stronger interactions in toluene compared to methanol solvents, consistent with the experimental results. Concurrently, we performed atomic force microscopy measurements using ZnO-coated probes for the short-ranged interaction. Our data provided valuable insights into another type of non-DLVO interaction, namely the repulsive solvation force. Specifically, the solvation force was stronger in water compared to ethanol and methanol, due to the stronger hydrogen bonding and denser packing of water molecules at the interface. In conclusion, our results highlight the importance of non-DLVO forces in a general framework for understanding and predicting particle aggregation and attachment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

On the melt pool dynamic of voxel-controlled metal matrix composites via hybrid additive manufacturing: Laser powder bed fusion and ink-jetting

In this study, the effect of the addition of reinforcement nanoparticles to the 316L matrix by adopting ex-situ and in-situ method (drop on demand jetting) to produce 316L/Al 2 O 3 nanocomposite was investigated. In the ex-situ method, the Al 2 O 3 nanoparticles (NPs) were lightly mixed with 316L powder and processed by laser powder bed fusion. In the in-situ method, an ethanol-based ink containing Al 13 nanoclusters (NCs) was added to 316L powder and then processed by laser. Both ex-situ and in-situ method produced nanocomposites with Al-Si-Mn-O-enriched precipitations within the 316L matrix. The addition of NPs/NCs to the 316L matrix, altered the geometrical characteristic of the single-track melt pools. At the same laser power, with increasing the amount of Al 2 O 3 NPs and Al 13 NCs the melt pool deepened due to reduced thermal conductivity and prolonged liquid presence. Further, as a result, 316L/1 wt% Al 13 NCs deposited single track showed larger grains in comparison to 316L single track. At a high laser power of 150W, the Marangoni flow and the buoyancy force caused the nanoparticles to agglomerate and float to the top surface of tracks; therefore, the wt% fraction of precipitation was drastically reduced due to the loss of Al. The 316L/Al 2 O 3 NPs and 316L/Al 13 NCs exhibited the microhardness of 285 ± 13 HV and 293 ± 7 HV, respectively, higher than the deposited 316L single track, 265 ± 15 HV. Lastly, a hybrid LPBF+ink-jet printer was adopted to selectively change the composition of different zones by adding Al 13 NCs ink to 316L and producing a voxel-controlled metal matrix composite.

316L↗
DOE OSTI2024

Carbon Nanospheres Loaded with Ir Single Atoms: Enhancing the Activity toward Formic Acid Oxidation by Increasing the Porosity

Theoretically, single-atom catalysts (SACs) offer 100 % atom utilization, making them strong candidates to replace expensive nanoparticles for catalysis. However, the structural supports used to anchor the SACs dramatically reduce the utilization efficiency of atoms ( i. e ., the percent of atoms actually accessible by reactants) by either encapsulating the SACs completely or creating severe diffusion limitation. Either of which leads to an overall low atom utilization and thus poor electrocatalytic activity similar to that of nanoparticles. In addressing this issue, we systematically investigated how the porous structure of carbon nanospheres affects the activity of Ir-SACs toward formic acid oxidation (FAO). Specifically, we utilized a kinetically-controlled growth strategy to produce uniform carbon nanospheres featuring yolk-shell, mesoporous, and hollow structures with Ir-SACs loaded throughout the structure. At a high specific surface area of 441 m 2 g -1 and exposed metal content of 1.82 wt %, the Ir-SACs based on mesoporous carbon nanospheres showed a remarkable FAO peak current density of 30.6 mA cm -2 , which was 283 and 46 times greater when benchmarked against the catalysts based on solid carbon nanospheres and 20 wt % Ir/C, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Spectroscopic Characterization of Highly Active Fe–N–C Oxygen Reduction Catalysts and Discovery of Strong Interaction with Nafion Ionomer

Scaling up clean-energy applications necessitates the development of platinum group metal (PGM)-free fuel cell electrocatalysts with high activity, stability, and low cost. Here, X-ray absorption (XAS) at the Fe K-edge and Fe K β X-ray emission (XES) spectroscopies were used to study the electronic structure of Fe centers in highly active Fe–N–C oxygen reduction catalysts with significant commercial potential. X-ray absorption near-edge structure (XANES) analysis has shown that the majority (>95%) of Fe centers are in the Fe 3+ oxidation state, while extended X-ray absorption fine structure (EXAFS) detected a mixture of single site Fe–N 4 centers (>95%) and centers with short (~2.5 Å) Fe–Fe interactions of Fe metal and/or Fe-carbide nanoparticles (<5%) featuring the Fe o oxidation state. Surprisingly, addition of Nafion, the most widely used ionomer, resulted in pronounced changes in the XAS spectra, consistent with a strong catalyst–ionomer interaction where long Fe–Fe interactions at ~3.1 Å were shown to be a feature of Fe 3+ ions bound with the Nafion. We conclude that exposure to Nafion during the device formulation has a different effect from the aggressive acid leaching typically used in the preparation of Fe–N–C catalysts. Furthermore, it was hypothesized that the polymer interacts with single sites’ Fe 3+ centers, as well as with graphene layers protecting the Fe o nanoparticles, and extracts some Fe ions into the Nafion matrix.

25 ENERGY STORAGE↗
DOE OSTI2021

Development of Multi-Scale X-ray Fluorescence Tomography for Examination of Nanocomposite-Treated Biological Samples

Research in cancer nanotechnology is entering its third decade, and the need to study interactions between nanomaterials and cells remains urgent. Heterogeneity of nanoparticle uptake by different cells and subcellular compartments represent the greatest obstacles to a full understanding of the entire spectrum of nanomaterials’ effects. In this work, we used flow cytometry to evaluate changes in cell cycle associated with non-targeted nanocomposite uptake by individual cells and cell populations. Analogous single cell and cell population changes in nanocomposite uptake were explored by X-ray fluorescence microscopy (XFM). Very few nanoparticles are visible by optical imaging without labeling, but labeling increases nanoparticle complexity and the risk of modified cellular uptake. XFM can be used to evaluate heterogeneity of nanocomposite uptake by directly imaging the metal atoms present in the metal-oxide nanocomposites under investigation. While XFM mapping has been performed iteratively in 2D with the same sample at different resolutions, this study is the first example of serial tomographic imaging at two different resolutions. A cluster of cells exposed to non-targeted nanocomposites was imaged with a micron-sized beam in 3D. Next, the sample was sectioned for immunohistochemistry as well as a high resolution “zoomed in” X-ray fluorescence (XRF) tomography with 80 nm beam spot size. Multiscale XRF tomography will revolutionize our ability to explore cell-to-cell differences in nanomaterial uptake.

60 APPLIED LIFE SCIENCES↗