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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Controlled Self-Assembly and Tuning of Large PbS Nanoparticle Supercrystals

Self-assembly of colloidal nanocrystals (NCs) into ordered superlattices (SLs) and supercrystals (SCs) enables new artificial NC solids for nanoelectronic and nanophotonic applications, which requires critical control of nucleation and growth conditions. In this paper, large SCs of PbS NCs up to ~100 μm size were synthesized by two controlled self-assembly methods from NC solutions. Both translational symmetry and orientational ordering of the nanocrystals in the SCs were readily tuned by excess oleic acid ligands and antisolvents. Slow evaporation and the counterdiffusion method of solvents resulted in the formation of single SCs with two different SLs from the same PbS NCs: a face-centered cubic SL with weak yet complex orientational order or a body-centered cubic SL with strong and uniform particle orientation, respectively. The translational ordering was mainly determined by the effective shape of the NCs while the difference in orientational order was a result of the balance between ligand–ligand attraction and rotational entropy. Finally, the ease of the growth of large SC solids could lead to diverse NC systems and facilitate essential investigation of nanoparticle interactions and coupling based nanoelectronic and nanophotonic properties.

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

Intrinsic Role of Cationic Substitution in Tuning Li/Ni Mixing in High-Ni Layered Oxides

Nickel-rich transition metal (TM) layered oxides, particularly those ones with high Ni content, attract world-wide interest for potential use as high-capacity cathodes in next-generation Li-ion batteries. However, as Ni loading increases, Li and Ni sitting at octahedra tend to mix, resulting in reduced electrochemical activity, which has been one major obstacle to their practical applications. We investigate the kinetic and thermodynamic aspects of Li/Ni mixing in LiNi 0.7 MnxCo 0.3-x O 2 (0≤x≤0.3) as they are being synthesized, through a multimodal approach for quantitative determination of structural ordering and com-parison to ab initio calculations. Results from this study elucidate the role of Mn/Co substitution at Ni sites in tuning Li/Ni ordering, intrinsically through local magnetic interaction. Specifically, Co substitution facilitates Li/Ni ordering by relieving the intra-plane magnetic frustration and reducing the inter-plane super-exchange (SE) interaction; in contrast, Mn exacerbates mag-netic frustration, strengthens SE, thereby aggravating Li/Ni mixing. These findings highlight the interplay between local magnetic interactions and cationic ordering, which has yet to be fully investigated for the needs of designing high-Ni layered cathodes and, broadly, TM-based oxides for various applications.

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

Tuning the Properties of Zr 6 O 8 Nodes in the Metal Organic Framework UiO-66 by Selection of Node-Bound Ligands and Linkers

The metal organic framework (MOF) UiO-66, which incorporates Zr 6 O 8 nodes, exhibits high stability under a wide range of conditions that commends it for potential applications. The MOF properties can be tuned by the choice of the groups bonded to the node defect sites and to the linkers. In this paper, we report data for UiO-66 incorporating formate, acetate, benzoate, and trifluoroacetate on the nodes and -NH 2 , -OH, -NO 2 , and phenyl substituents on the benzene rings of the benzene-1,4-dicarboxylic acid-derived linkers. The MOFs were characterized by IR and 1 H NMR spectroscopies, thermal gravimetric analysis, N 2 adsorption, X-ray diffraction crystallography, scanning and transmission electron microscopy, and electronic structure calculations. The ligands on the nodes were identified and quantified by 1 H NMR spectra of the MOFs digested in NaOH/D 2 O solutions. Lastly, the effects of the node and linker groups on the electronic properties of the nodes have been quantified with IR spectra of the node μ 3 -OH groups and by density functional theory calculations, which are in good agreement with one another.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

From Waste-Heat Recovery to Refrigeration: Compositional Tuning of Magnetocaloric Mn 1+ x Sb

Magnetic refrigeration, as well as waste-heat recovery, can be accomplished through the magnetocaloric effect, where temperature changes the magnetic state of a material or vice versa. Promising magnetocaloric materials display large changes in magnetic entropy (ΔS M ) upon application of a moderate magnetic field and are often associated with magnetic materials possessing some degree of magnetostructural coupling. In such compounds, the magnetic transition is coupled to some structural transition at the ordering temperature, and indicators for these are readily calculated by the magnetic deformation proxy Σ M . MnSb, with a Curie temperature T C = 577 K, has a calculated magnetic deformation of Σ M = 5.9% and is a promising candidate material for waste-heat recovery. The temperature dependence of structural, magnetic, and magnetocaloric properties of Mn 1+ x Sb, where $x$ is a tunable amount of interstitial Mn, is studied here. specifically, excess Mn is incorporated as an interstitial whose magnetic moment is antialigned with the stoichiometric Mn, and the excess Mn has the effect of lowering T C , such that the Curie temperature can be tuned from 577 K to nearly room temperature at 318 K for $x$ = 0.2. For $x$ = 0.0, 0.1, and 0.2, values of ΔS M under a maximum magnetic field $H$ = 5 T are found to be 3.65, 3.00, and 2.83 J K -1 kg -1 , respectively. While the maximum ΔS M decreases with $x$, the high refrigerant capacity a more holistic measure of performance-is retained in this highly tunable system.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tuning the Luminescence of Layered Halide Perovskites

Layered halide perovskites offer a versatile platform for manipulating light through synthetic design. Although most layered perovskites absorb strongly in the ultraviolet (UV) or near-UV region, their emission can range from the UV to the infrared region of the electromagnetic spectrum. This emission can be very narrow, displaying high color purity, or it can be extremely broad, spanning the entire visible spectrum and providing high color rendition (or accurately reproducing illuminated colors). The origin of the photoluminescence can vary enormously. Strongly correlated electron–hole pairs, permanent lattice defects, transient light-induced defects, and ligand-field transitions in the inorganic layers and molecular chromophores in the organic layers can be involved in the emission mechanism. Here in this review, we highlight the different types of photoluminescence that may be attained from layered halide perovskites, with an emphasis on how the emission may be systematically tuned through changes to the bulk crystalline lattice: changes in composition, structure, and dimensionality.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Tuning the Morphology and Electronic Properties of Single-Crystal LiNi 0.5 Mn 1.5 O 4-δ : Exploring the Influence of LiCl–KCl Molten Salt Flux Composition and Synthesis Temperature

Single-crystal materials have played a unique role in the development of high-performance cathode materials for Li batteries due to their favorable chemomechanical stability. The molten salt synthesis method has become one of the most prominent techniques used to synthesize single-crystal layered and spinel materials. In this work, the molten salt synthesis method is used as a technique to tune both the morphology and Mn 3+ content of high-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) cathodes. The resulting materials are thoroughly characterized by a suite of analytical techniques, including synchrotron X-ray core-level spectroscopy, which are sensitive to the material properties on multiple length scales. Furthermore, the multidimensional characterization allows us to build a materials library according to the molten salt phase diagram as well as to establish the relationship among synthesis, material properties, and battery performance. The results of this work show that the Mn 3+ content is primarily dependent on the synthesis temperature and increases as the temperature is increased. Additionally, the particle morphology is mostly dependent on the composition of the molten salt flux, which can be tailored to obtain well-defined octahedrons enclosed by (111) facets, plates with predominant ($11\tilde{2}$) facets, irregularly shaped particles, or mixtures of these. The electrochemical measurements indicate that the Mn 3+ content has a larger contribution to the battery performance of LNMO than do morphological characteristics and that a significant amount of Mn 3+ could become detrimental to the battery performance. However, with similar Mn 3+ contents, morphology still plays a role in influencing the battery cycle life and rate performance. The insights of molten salt synthesis parameters on the formation of LNMO, with deconvolution of the roles of Mn 3+ and morphology, are crucial to continuing studies in the rational design of LNMO cathode materials for high-energy Li batteries.

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

Tuning the Structural and Magnetic Properties in Mixed Cation Mn x Co 2– x P 2 S 6

The metal thiophosphates (MTP), M 2 P 2 S 6, are a versatile class of van der Waals materials, which are notable for the possibility of tuning their magnetic properties with the incorporation of different transition-metal cations. Further, they also offer opportunities to probe the independent and synergistic role of the magnetically active cation sublattice when coupled to P 2 Q 6 polyhedra. Herein, we report the structural, magnetic, and electronic properties of the series of MTPs, Mn x Co 2– x P 2 S 6 ( x = 0.25, 0.5, 1, 1.5, 1.75) synthesized by the P 2 S 5 flux method. In this work, structural and elemental analysis indicates a homogeneous stoichiometry in the Mn x Co 2– x P 2 S 6 compounds. We observe that a correlation is apparent between the intensities of specific Raman modes and Raman shifts with respect to the alloying ratio between Mn and Co. Magnetic susceptibility measurements indicate that the alloyed systems adopt an ordered antiferromagnetic (AFM) configuration with a dependence of the Néel temperature on the alloying ratio. A possible magnetic frustration behavior was observed for the composition MnCoP 2 S 6 due to magnetic moment compensation as the alloying ratio between Mn and Co approaches parity. Interestingly, mixed oxidation states of the metal cation species are also observed in Mn x Co 2– x P 2 S 6 along with a linear dependence of the work function on the alloying ratio of Mn and Co.

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

Cobalt(II) Phthalocyanine Substituents Tune the Electrocatalytic CO 2 Conversion to Methanol

Cobalt phthalocyanine (Co(II)Pc) and its derivatives are promising molecular electrocatalysts for the electrochemical reduction of CO 2 to CO and methanol (CH 3 OH). Despite increasing interest, a detailed mechanistic understanding of how ligand substituents influence catalytic activity, selectivity, and efficiency remains limited. In this study, we employ density functional theory (DFT) to systematically investigate the influence of electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) on the electronic structure and redox properties of the Co(II)Pc electrocatalyst, and to elucidate CO 2 RR mechanistic pathways. Our results reveal that EWGs cause a positive shift in the reduction potentials, favor CO 2 binding over protonation of the Co metal center and promote downstream methanol formation at mild potentials. EDGs show opposite trends including favorable protonation steps, promoting a negative shift in the reduction potential, and facilitating the hydrogen evolution reaction (HER), which competes with the desired CO 2 RR pathway. Notably, CO dissociation is thermodynamically and kinetically unfavorable across all systems, positioning the redox potential versus CO dissociation energy as a key factor for methanol selectivity. Furthermore, these insights provide a predictive framework for rational catalyst design and underscore the critical role of electronic tuning in advancing molecular electrocatalysts for sustainable CO 2 conversion.

Alcohols↗
DOE OSTI2026

Compositional Tuning of Magnetic Properties in a Series of Transition Metal Site-Deficient UCo x Bi 2 and UNi x Bi 2 Phases

Varying the electronic structure of topological materials through aliovalent substitution is a primary approach to tuning their physical properties. Unlike substitution, metal site deficiency intrinsic to some structure types, including HfCuSi 2 -type, has rarely been employed for controlling the properties of topological phases. In this report, we describe the synthesis and characterization of two new series of compounds, UCoxBi 2 and UNixBi 2 , which demonstrate the variation of transition metal content through synthetic conditions. Magnetic measurements reveal the dependence between the extent of transition metal incorporation and the magnetism of the resulting phase. DFT calculations demonstrated the ability to model their formation and predict the stability ranges of transition metal-site deficient compounds.

Crystal structure↗
DOE OSTI2018

From Transition Metals to Lanthanides to Actinides: Metal-Mediated Tuning of Electronic Properties of Isostructural Metal–Organic Frameworks

In this study, isostructural metal-organic frameworks (MOFs) have been prepared from a variety of metal-oxide clusters, including transition metals, lanthanides, and actinides. Experimental and calculated shifts in O–H stretching frequencies for hydroxyl groups associated with the metal-oxide nodes reveal varying electronic properties for these units, thereby offering opportunities to tune support effects for other materials deposited onto these nodes.

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

Enhancing CO Oxidation Activity via Tuning a Charge Transfer Between Gold Nanoparticles and Supports

Charge transfer from the supports to nanoparticles at the interface is one of the key factors to determine the catalytic performances of supported nanoparticles. In this work, we revealed that the charge transfer from semiconductor support to Au nanoparticle catalysts enhanced their activity toward CO oxidation. In this work, a novel Au/SiO 2 /Si composite system with precisely controllable SiO 2 layer thickness was fabricated to tune the magnitude of interfacial charge transfer. With the support of X-ray photoelectron spectroscopy and numerical simulations, it was demonstrated that the Schottoky barrier formed across the Au/SiO 2 /Si heterojunction led to negative charge accumulation at the surface of Au nanoparticles, which may be transferred to the antibonding orbitral of adsorbed O 2 molecules to the O-O bonds. This discovery highlights a new perspective in explaining the role of strong metal-support interactions for catalytic reactions and provides a fresh path for designing the next generation of nanocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tuning Strong Metal–Support Interaction Kinetics on Pt-Loaded TiO 2 (110) by Choosing the Pressure: A Combined Ultrahigh Vacuum/Near-Ambient Pressure XPS Study

Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal–support interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the “pressure gap” between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O 2 and H 2 on the SMSI-state of well-defined Pt/TiO 2 (110) catalysts at pressures of up to 0.1 Torr. Further, by tuning the O 2 pressure, we can either selectively oxidize the TiO 2 support or both the support and the Pt particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1 × 10 –5 Torr O 2 , but orders of magnitude less effectively at higher O 2 pressures, where Pt is in an oxidic state. While the oxidation/reduction of Pt particles is reversible, they remain embedded in the support once encapsulation has occurred.

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

Tuning Self-Assembly of Gold Nanoparticles Grafted with Charged Polymers by Varying Temperature and Electrolytes

Here, we report on the assembly of gold nanoparticles (AuNPs, 5 and 10 nm core diameters) grafted with poly(ethylene glycol) (PEG) terminated with either positively (–NH 2 ) or negatively charged (–COOH) end groups. We employ synchrotron-based small-angle X-ray scattering (SAXS) techniques to investigate the effect of electrolytes and temperature on the assembly and crystallization behavior of these grafted AuNPs. Our studies reveal that –NH 2 -grafted AuNPs spontaneously assemble into a layered hexagonal structure that deteriorates upon adding K 2 CO 3 to the suspension. The hexagonal structure recovers after heating the same suspension above 60 °C. On the other hand, the COOH-terminated AuNPs remain dispersed in the suspensions and assemble and crystallize into a face-centered cubic structure only in the presence of K 2 CO 3 at temperatures above 60 °C. Varying the pH of the –NH 2 -terminated AuNP suspensions induces short-range order (SRO) structures with a single characteristic length scale that shrinks upon heating. Similarly, SRO for the –COOH-terminated AuNP is realized only by lowering the pH. This study demonstrates the use of electrolytes and temperature on the surface charge of grafted AuNPs as knobs to tune self-assembly and crystallization.

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

Tuning Fabrication Factors for Reduced Graphene Oxide Forward Osmosis Membranes

Forward osmosis (FO) may serve as a near-zero energy approach for wastewater management and selective chemical enrichment with an appropriate FO membrane. There is a need for novel FO membranes with better physical stability, chemical compatibility, and enhanced reverse flux selectivity. In this work, we have systematically studied a variety of factors for fabricating thermally reduced graphene oxide (RGO) FO filtration membranes and have demonstrated that with a comparable water flux, the RGO membranes have an exceptionally large reverse flux selectivity with 1.5 M sodium sulfate draw solution, about 7 times larger than that of cellulose triacetate membranes under the same testing condition. The interlayer spacing of the membranes can be fine-tuned by varying temperatures, so that the free interlayer spacing is less than 0.7 nm after exposure to water. The RGO-based membranes offer a few advantages with high reverse flux selectivity, mechanical robustness with strong adhesion to nylong support membranes without damage after FO tests and tape peel tests, and enhanced chromate and chlorine resistance. Finally, we have further demonstrated that in the FO processes, one can concentrate waste brine while simultaneously harvesting the osmotic energy as electricity, offering potential applications of forward osmosis-based osmotic batteries for powering electronic devices.

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

Fundamental Insights into Cathode Stability: Linking Compositional Tuning and Local Coordination in Complex Metal Oxides under Aqueous Transformations

Compositional tuning of complex metal oxides in Li-ion battery materials influences their performance as well as their end-of-life behavior, in particular, the tendency to release toxic metal cations in aqueous solution. We modeled ternary variants of a parent LiCoO 2 delafossite structure by varying the metal identity and relative amounts. This yielded ten model formulations of Li(A 4/6 B 1/6 C 1/6 )O 2 , where the material is enriched with the A metal and doped with B and C, with Ni, Mn, Co, Fe, Al, V, and Ti as constituent metals. To assess their stability in aqueous conditions, metal release energetics were calculated using a combination of Density Functional Theory calculations and thermodynamics. Metal release in ternary oxides is dictated by subtle variations in the coordination environment of the leaving group. To identify governing chemical features across diverse compositions with varying local coordination environments, we leverage random forest regression and descriptor importance analysis. A key result is that metal–oxygen orbital hybridization, quantified using a projected density-of-states-derived descriptor, H d/p , provides a physically grounded measure of interaction strength that governs metal release energetics. This refined perspective goes beyond conventional oxidation state considerations and offers more robust insights for materials science. Finally, we model defect surface-bound O 2 dimer formation as a proxy for reactive oxygen species (ROS) generation. The results show that Ni-rich compositions more readily stabilize spin-polarized O 2 dimers, corroborating experimental reports of an increased ROS-driven biological response. In conclusion, our results establish a compositional and electronic basis for metal release and surface oxygen reactivity that form a rationale for complex metal oxide design principles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tuning the Deoxygenation of Bulk-Dissolved Oxygen in Copper

Using synchrotron-based ambient-pressure X-ray photoelectron spectroscopy, we report the tuning of the deoxygenation process of bulk dissolved oxygen in copper via a combination of H 2 gas flow and elevated temperature. Here, we show that a critical temperature of ~580 °C exists for driving segregation of bulk dissolved oxygen to form chemisorbed oxygen on the Cu surface, which subsequently reacts with hydrogen to form OH species and then H 2 O molecules that desorb from the surface. This deoxygenation process is tunable by a progressive stepwise increase of temperature that results in surface segregation of oxygen from deeper regions of bulk Cu. Using atomistic simulations, we show that the bulk-dissolved oxygen occupies octahedral sites of the Cu lattice and the deoxygenation process involves oxygen migration between octahedral and tetrahedral sites with a diffusion barrier of ~0.5 eV.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Tuning Binding Tendencies of Small Molecules in Metal–Organic Frameworks with Open Metal Sites by Metal Substitution and Linker Functionalization

Metal-organic frameworks (MOFs) with open metal sites (OMS) are known to be selective for ethylene relative to ethane. In practical applications of this separation, the presence of other small molecules such as H 2 O, CO, and C 2 H 2 may affect the suitability of sorbents. We used density functional theory (DFT) calculations to compute the binding energies of H 2 O, CO, C 2 H 2 , C 2 H 4 , and C 2 H 6 in M-BTC (BTC = 1,3,5-benzenetricarboxylic acid) with 12 different metals forming OMS (M = Mg, Ti, V, Cr, Mo, Mn, Fe, Ru, Co, Ni, Cu, and Zn). To probe the generality of these results for MOFs containing other ligands, we performed similar calculations for metal-substituted MOFs based on four more materials with dimeric Cu sites. Here, our results provide useful insights into the variations in binding energies that are achievable by metal substitution in this broad class of MOFs, as well as pointing towards feasible adsorption-based separation strategies for complex molecular mixtures. Zn OMS MOFs were predicted to have the highest C 2 H 4 /C 2 H 6 selectivity, but the strong binding energy of solvents and other small molecules in these materials may create practical challenges. Finally, we used DFT calculations to examine whether functionalizing linkers in these materials with electron withdrawing (-fluorine) and donating (-methyl) groups offer a useful way to tune molecular binding energies on OMS in these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Morphological Tuning of Nanoporous Metals Prepared with Conversion Reaction Synthesis via Thermal Annealing

We report that conversion reaction synthesis, namely, reacting an organolithium reducing agent with a metal chloride to produce a metal/LiCl nanocomposite and then removing lithium chloride with a polar organic solvent, is an efficient and scalable way to fabricate a variety of three-dimensional, bicontinuous nanoporous transition metals. Thermal annealing was investigated as a means to tune the morphology of these nanoporous metals. X-ray diffraction studies were used to investigate the effect of thermal annealing on the size and strain of phases in Cu/ LiCl, Co/LiCl, and Fe/LiCl nanocomposites, while electron microscopy and nitrogen adsorption studies were used to study the porosity and surface properties of the resulting nanoporous metals after LiCl was removed from the annealed nanocomposites. Annealing metal/LiCl nanocomposites resulted in the controlled growth of the metal nanoparticles, the rate of which depended on the diffusivity of the metal. It was observed that annealing nanocomposites produced more robust nanoporous metals with increased porosity under certain conditions. In conclusion, it was found that annealing the as-formed nanocomposites rather than the isolated nanoporous metals provides finer control of the conversion synthesis process and allows for the design of more optimized pore structures and thus enhanced suitability for catalytic and electrochemical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗