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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 OSTI2024

Screening of Cu-Based Catalysts for Selective Methane to Methanol Conversion

Developing selective catalysts for methane conversion to added value chemicals has been considered as a promising approach for efficient utilization of abundant natural gas resources. Here, we present a descriptor-based screening for high methane conversion and methanol selectivity at the interfaces between metal oxide clusters and Cu 2 O/Cu(111) support (MO x /Cu 2 O/Cu(111), M = Mg, Fe, Co, Ni, Cu, Zn, Ti, Zr, Sn, Ce) on exposure to the mixture of CH 4 /O 2 /H 2 O. Wherein, the activation energy of direct methane to methanol conversion, *OH + *CH 4 → *CH 3 OH + *H, and the ratio for adsorption energy of oxygen and water, E ads (O 2 )/E ads (H 2 O), are identified as the effective descriptor for methane conversion and methanol selectivity, respectively. Finally, by providing an exceptional oxygen and hydroxyl sites with high-lying O 2p states, the MgO/Cu 2 O/Cu(111) catalyst is found to be the most promising system among the systems studied, being able to provide the highest methane conversion with high methanol selectivity.

03 NATURAL GAS↗
DOE OSTI2025

Facilitating Screening of MOFs for Mixed Matrix Membranes Using Machine Learning and the Maxwell Model

Metal organic framework (MOF)-based mixedmatrix membranes (MMMs), which embed MOF particles in polymer matrices, combine the advantages of polymeric and inorganic membranes. Multiple previous studies have used the Maxwell model together with molecular simulations and machine learning (ML) to predict the performance of MOF/polymer MMMs. However, the assumption of rigid MOF frameworks in molecular simulations limited the accuracy of the data used in the predictions, particularly in predicting molecular diffusivities. We developed a novel workflow integrating ML models with consideration of MOF flexibility to predict the permeability and selectivity of 131,722 MMMs for CO 2 /CH 4 , O 2 /N 2 and He/H 2 separations. The full range of achievable MMM performance within the Maxwell model was analyzed, and several promising MOFs were identified using this workflow. This approach offers an efficient tool for screening any polymer and MOF combination in gas separation applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Chemical and Radiation Stability of Ionic Liquids: A Computational Screening Study

Using a variety of density functional theory (DFT) methods, we present a systematic computational screening effort to analyze the chemical and radiation stability for a large number of anions and cations that constitute room-temperature ionic liquids (RTILs). We compute various electronic properties such as the HOMO–LUMO gap, the ionization potential, and the electron affinities for a large library of ions (42 cations and 42 anions). The theoretical analysis provides the most comprehensive characterization of the chemical and radiation stability of individual ions in RTILs to date. Our calculations reveal that cation stability is closely related to constituent alkyl chain length and branching, whereas the anion stability is mostly dictated by ion size and electronegativity. Furthermore, these calculations show that the ωB97XD functional is the most internally consistent for predicting the chemical and radiation stability. In conclusion, these calculations establish a chemical stability database and a theoretical procedure for further experimental and computational studies of RTILs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Effects of Functional Groups in Redox-Active Organic Molecules: A High-Throughput Screening Approach

Nonaqueous redox flow batteries have attracted recent attention with their potential for high electrochemical storage capacity, with organic electrolytes serving as solvents with a wide electrochemical stability window. Organic molecules can also serve as electroactive species, where molecules with low reduction potentials or high oxidation potentials can provide substantial chemical energy. To identify promising electrolytes in a vast chemical space, high-throughput screening (HTS) of candidate molecules plays an important role, where HTS is used to calculate properties of thousands of molecules and identify a few organic molecules worthy of further attention in battery research. Here, in this work, we present reduction and oxidation potentials obtained from HTS of 4178 molecules. The molecules are composed of base groups of five- or six-membered rings with one or two functional groups attached, with the set of possible functional groups including both electron-withdrawing and electron-donating groups. In addition to observing the trends in potentials that result from differences in organic base groups and functional groups, we analyze the effects of molecular characteristics such as multiple bonds, Hammett parameters, and functional group position. In conclusion, this work provides useful guidance in determining how the identities of the base groups and functional groups are correlated with desirable reduction and oxidation potentials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Electrostatic Screening Modulates Analyte Binding and Emission of Carbon Nanotubes

Many nanomaterials are promising biosensor elements due to capabilities for transduction of biomolecular interactions into an electrical or optical signal. Certain nanomaterials have intrinsic charges and are thus susceptible to electrostatic forces that may enhance or attenuate their response. We are using a combination of experimental and computational approaches, we found and characterized a critical role of the solvent salt conditions in determining the extent of optical changes due to anionic analyte interaction with an intrinsically responsive nanomaterial, single-walled carbon nanotubes. Using a well-characterized model anionic analyte, we found that monovalent salts enabled greater optical changes of a polyanion-bound carbon nanotube in a highly dose-dependent manner but not with a neutrally charged analyte. Molecular dynamics simulations were used to derive a quantitative understanding of this mechanism from a free-energy perspective. We also show that salt can be used to enhance the sensitivity of detection for a polyanionic analyte. These results suggest that electrostatic screening is an important parameter for intrinsically charged nanoparticle sensors and it may be tuned to control the response to analytes.

36 MATERIALS SCIENCE↗
DOE OSTI2017

High-Throughput Computational Screening of Multivariate Metal–Organic Frameworks (MTV-MOFs) for CO 2 Capture

Multivariate metal–organic frameworks (MTV-MOFs) contain multiple linker types within a single structure. Arrangements of linkers containing different functional groups confer structural diversity and surface heterogeneity and result in a combinatorial explosion in the number of possible structures. Here, we carried out high-throughput computational screening of a large number of computer-generated MTV-MOFs to assess their CO 2 capture properties using grand canonical Monte Carlo simulations. The results demonstrate that functionalization enhances CO 2 capture performance of MTV-MOFs when compared to their parent (unfunctionalized) counterparts, and the pore size plays a dominant role in determining the CO 2 adsorption capabilities of MTV-MOFs irrespective of the combinations of the three functional groups (-F, -NH 2 , and -OCH 3 ) that we explored. We also found that the functionalization of parent MOFs with small pores led to larger enhancements in CO 2 uptake and CO 2 /N 2 selectivity than functionalization in larger-pore MOFs. Free energy contour maps are presented to visually compare the influence of linker functionalization between frameworks with large and small pores.

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

Hydrogen Bonding Inside Anionic Polymeric Brush Layer: Machine Learning-Driven Exploration of the Relative Roles of the Polymer Steric Effect, Charging, and Type of Screening Counterions

This paper employs a combination of all-atom molecular dynamics (MD) simulations and unsupervised machine learning (ML) for studying the water-water hydrogen bonds (HBs) inside the anionic poly-acrylic acid (PAA) brushes modeled using all-atom MD simulations. PAA brush layer with different charge fraction (f), namely f=0, f=0.25, and f=1, is considered. Water-water interactions, both inside and outside the brush layer, are represented through distinct clusters of tupules of variables representing distances associated with the interacting water molecules. While clusters representing the HBs are present for water inside and outside the brushes, several clusters representing the long-range water-water interactions are missing for the water molecules inside the highly charged (f=1) PAA brushes. More importantly, inside highly charged brushes, the edge of the clusters representing the water-water HBs is progressively shortened, as compared to that in the bulk. Both these results stem from the presence of the PAA brushes imparting the steric effect and the charge effect, or the effect associated with enhanced interactions of water molecules with PE charges and counterions, thereby disrupting the water connectivity. This water-charged-species interaction also increases the water-water HB angle, i.e., makes the water-water HBs less stable inside the highly charged PAA brush layer. The narrowing of the clusters representing the HBs and the alteration of the angle characterizing the HBs confirm that the conditions defining the water-water HBs change inside the PAA brush layer as a function of the charges on the PAA brush layer. Furthermore, we show that the use of the generic definition of HBs, as compared to using our simulation-motivated modified definition of water-water HBs, overpredict the number of water-water HBs inside the PAA brush layer. Finally, we employ this all-atom-MD-ML framework to quantify the effect of other types of screening counterions (Li + , Ca 2+ , and Y 3+ ions) in determining the water-water interactions and water-water HB properties inside the PAA brush layer. Furthermore, the findings of the present study, confirming the weakening of water-water HBs inside the PAA brush layer, points to the possibility that the water molecules will be more available for hydrating the brush layer and counterions, thereby leading to a more pronounced wetting of the PAA brush layer.

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

Charged Bosons Made of Fermions in Bilayer Structures with Strong Metallic Screening

Two-dimensional monolayer structures of transition metal dichalogenides (TMDs) have been shown to allow many higher-order excitonic bound states, including trions (charged excitons), biexcitons (excitonic molecules), and charged biexcitons. Here, we report here experimental evidence and the theoretical basis for a new bound excitonic complex, consisting of two free carriers bound to an exciton in a bilayer structure. Our experimental measurements on structures made using two different materials show a new spectral line at the predicted energy with two different TMD materials (MoSe 2 and WSe 2 ) with both n- and p-doping, if and only if all the required theoretical conditions for this complex are fulfilled, in particular, only in the presence of a parallel metal layer that significantly screens the repulsive interaction between the like-charge carriers. Because these four-carrier bound states are charged bosons, they could eventually be the basis for a new path to superconductivity without Cooper pairing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Environmental Screening Effects in 2D Materials: Renormalization of the Bandgap, Electronic Structure, and Optical Spectra of Few-Layer Black Phosphorus

Few-layer black phosphorus has recently emerged as a potential 2D semiconductor, notable for its widely tunable bandgap, highly anisotropic properties, and theoretically predicted large exciton binding energies. To avoid degradation, it has become common practice to encapsulate black phosphorus devices. It is generally assumed that this encapsulation does not qualitatively affect their optical properties. In this work, we show that the contrary is true. We have performed ab initio GW and GW plus Bethe–Salpeter equation (GW-BSE) calculations to determine the quasiparticle (QP) band structure and optical spectrum of one-layer (1L) through four-layer (4L) black phosphorus, with and without encapsulation between hexagonal boron nitride and sapphire. We show that black phosphorus is exceptionally sensitive to environmental screening. Encapsulation reduces the exciton binding energy in 1L by as much as 70% and completely eliminates the presence of a bound exciton in the 4L structure. The reduction in the exciton binding energies is offset by a similarly large renormalization of the QP bandgap so that the optical gap remains nearly unchanged, yet the nature of the excited states and the qualitative features of the absorption spectrum change dramatically.

2D materials↗
DOE OSTI2021

Machine Learning Screening of Metal-Ion Battery Electrode Materials

Here, in this work we present deep neural network regression machine learning models (ML) for predicting the average voltage and the percentage change in volume of battery electrodes upon charging and discharging with metal ions. Our models exhibit good performance as measured by the average mean absolute error obtained from a 10-fold cross-validation as well as on independent test sets. We further assess the robustness our ML models by investigating their screening potential beyond the training database. We produce novel Na-ion electrodes by systematically replacing Li-ions in the original database by Na-ions, and then selecting a set of 22 electrodes that exhibit a good performance in energy density as well as small volume variations upon charging and discharging, as predicted by the machine learning model. The ML predictions for these new materials are then compared to quantum-mechanics based calculations. Our results reaffirm the significant role of machine learning techniques in the exploration of materials for battery applications.

,electrode volume change↗
DOE OSTI2026

Large Polaron Screening Delays Mobility Roll-Off in Halide Perovskites under High Injection

The interplay between carrier density regimes and the various scattering processes is fundamental for understanding charge transport efficiency in high-performance semiconductors. Combining ultrafast time-resolved terahertz spectroscopy (TRTS) and transient microwave photoconductivity (TRMC), we measure carrier mobilities over 7 orders of magnitude (10 13 –10 20 carriers cm –3 ), reaching a regime where carrier–carrier scattering dominates and mobility begins to roll off. We find the Caughey–Thomas model can be effectively employed for transport modeling in 3D metal halide perovskites (MHPs), and the mobility roll-off near ∼10 19 cm –3 can be tuned by MHP composition. Carrier lifetime in MHPs starts decreasing at much lower carrier densities due to interband multi-carrier recombination, while intraband carrier mobility remains unchanged as carrier–carrier scattering is screened by the presence of polarons. The validated Caughey–Thomas model provides a practical input for device simulations, prevents overestimation of diffusion length under high injection, and suggests that MHPs are excellent candidates for unipolar device applications under high carrier densities.

14 SOLAR ENERGY↗
DOE OSTI2024

A Structurally Diverse Compound Screening Library to Identify Substrates for Diamine, Polyamine, and Related Acetyltransferases

Spermidine/spermine N-acetyltransferases (SSATs) and other types of polyamine acetyltransferases (PAATs) acetylate diamines and/or polyamines. These enzymes are evolutionarily related and belong to the Gcn5-related N-acetyltransferase (GNAT) superfamily, yet we lack a fundamental understanding of their substrate specificity and/or promiscuity toward different compounds. Many of these enzymes are known or are predicted to acetylate polyamines, but in the cell there are other types of compounds that contain moieties derived from polyamines that may be the native substrates for these enzymes. To learn more about the identity of substrates that are acetylated, we selected and screened 17 different GNAT enzymes for activity toward a set of structurally diverse compounds that contained different types of amine moieties (e.g., aminopropyl, aminobutyl, etc.). These compounds included diamines, triamines, and polyamines containing primary amino groups, and they had structural diversity with variation of the chain length and presence or absence of internal amino groups and other functional groups. We found 12 of the 17 enzymes acetylated at least one of the compounds. Some enzymes were selective toward acetylating only one compound while others exhibited substrate promiscuity toward numerous compounds. Our experimental results ultimately allowed us to pinpoint specific substrates that could be further investigated to more fully understand substrate specificity versus promiscuity of GNAT enzymes and the role of acetylated small molecules in cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Computation-Ready, Experimental Metal–Organic Frameworks: A Tool To Enable High-Throughput Screening of Nanoporous Crystals

We report that experimentally refined crystal structures for metal-organic frameworks (MOFs) often include solvent molecules and partially occupied or disordered atoms. This creates a major impediment to applying high-throughput computational screening to MOFs. To address this problem, we have constructed a database of MOF structures that are derived from experimental data but are immediately suitable for molecular simulations. The Computation-Ready, Experimental (CoRE) MOF database contains over 4,700 porous structures with publically available atomic coordinates. Important physical and chemical properties including the surface area and pore dimensions are reported for these structures. To demonstrate the utility of the database, we performed grand canonical Monte Carlo simulations of methane adsorption on all structures in the CoRE MOF database. Lastly, we investigated the structural properties of the CoRE MOFs that govern methane storage capacity and found that these relationships agree well with those derived recently from a large database of hypothetical MOFs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Rapid Screening of Lanthipeptide Analogs via In-Colony Removal of Leader Peptides in Escherichia coli

Most native producers of ribosomally synthesized and post-translationally modified peptides (RiPPs) utilize N-terminal leader peptides to avoid potential cytotoxicity of mature products to the hosts. Unfortunately, the native machinery of leader peptide removal is often difficult to reconstitute in heterologous hosts. Here in this paper we devised a general method to produce bioactive lanthipeptides, a major class of RiPP molecules, in Escherichia coli colonies using synthetic biology principles, where leader peptide removal is programmed temporally by protease compartmentalization and inducible cell autolysis. We demonstrated the method for producing two lantibiotics, haloduracin and lacticin 481, and performed analog screening for haloduracin. This method enables facile, high throughput discovery, characterization, and engineering of RiPPs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Maximizing Diversity from a Kinase Screen: Identification of Novel and Selective pan-Trk Inhibitors for Chronic Pain

We have identified several series of small molecule inhibitors of TrkA with unique binding modes. The starting leads were chosen to maximize the structural and binding mode diversity derived from a high throughput screen of our internal compound collection. These leads were optimized for potency and selectivity employing a structure based drug design approach adhering to the principles of ligand efficiency to maximize binding affinity without overly relying on lipophilic interactions. This endeavor resulted in the identification of several small molecule pan-Trk inhibitor series that exhibit high selectivity for TrkA/B/C versus a diverse panel of kinases. We have also demonstrated efficacy in both inflammatory and neuropathic pain models upon oral dosing. Herein we describe the identification process, hit-to-lead progression, and binding profiles of these selective pan-Trk kinase inhibitors.

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

Polarization screening-induced magnetic phase gradients at complex oxide interfaces

Thin-film oxide heterostructures show great potential for use in spintronic memories, where electronic charge and spin are coupled to transport information. Here we use a La 0.7 Sr 0.3 MnO 3 (LSMO)/PbZr 0.2 Ti 0.8 O 3 (PZT) model system to explore how local variations in electronic and magnetic phases mediate this coupling. We present direct, local measurements of valence, ferroelectric polarization and magnetization, from which we map the phases at the LSMO/PZT interface. We combine these experimental results with electronic structure calculations to elucidate the microscopic interactions governing the interfacial response of this system. We observe a magnetic asymmetry at the LSMO/PZT interface that depends on the local PZT polarization and gives rise to gradients in local magnetic moments; this is associated with a metal–insulator transition at the interface, which results in significantly different charge-transfer screening lengths. This work establishes a framework to understand the fundamental asymmetries of magnetoelectric coupling in oxide heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Screened moments and extrinsic in-gap states in samarium hexaboride

Samarium hexaboride (SmB 6 ) is a Kondo insulator, with a narrow gap due to hybridization between localized and conduction electrons. Despite being an insulator, many samples show metal-like properties. Rare-earth purification is exceedingly difficult, and nominally pure samples may contain 2% or more of impurities. Here to determine the effects of rare-earth doping on SmB6, we synthesized and probed a series of gadolinium-doped samples. We found a relationship between specific heat and impurity moment screening which scales systematically. Consistent with this finding, our neutron scattering experiments of a high purity sample of doubly isotopic 154 Sm 11 B 6 show no intrinsic excitations below the well-established 13 meV spin-exciton. The result of introducing impurities into a Kondo insulator is incompletely understood, but it is clear from our measurements that there is a systematic relationship between rare-earth impurities and metal-like properties in SmB 6 .

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

Exceptional hydrogen storage achieved by screening nearly half a million metal-organic frameworks

Few hydrogen adsorbents balance high usable volumetric and gravimetric capacities. Although metal-organic frameworks (MOFs) have recently demonstrated progress in closing this gap, the large number of MOFs has hindered the identification of optimal materials. Here, a systematic assessment of published databases of real and hypothetical MOFs is presented. Nearly 500,000 compounds were screened computationally, and the most promising were assessed experimentally. Three MOFs with capacities surpassing that of IRMOF-20, the record-holder for balanced hydrogen capacity, are demonstrated: SNU-70, UMCM-9, and PCN-610/NU-100. Analysis of trends reveals the existence of a volumetric ceiling at ~ 40 g H 2 L -1 . Surpassing this ceiling is proposed as a new capacity target for hydrogen adsorbents. Counter to earlier studies of total hydrogen uptake in MOFs, usable capacities in the highest-capacity materials are negatively correlated with density and volumetric surface area. Instead, capacity is maximized by increasing gravimetric surface area and porosity. This suggests that property/performance trends for total capacities may not translate to usable capacities.

36 MATERIALS SCIENCE↗