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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

3D Printing of Solution‐Processable 2D Nanoplates and 1D Nanorods for Flexible Thermoelectrics with Ultrahigh Power Factor at Low‐Medium Temperatures

Abstract Solution‐processable semiconducting 2D nanoplates and 1D nanorods are attractive building blocks for diverse technologies, including thermoelectrics, optoelectronics, and electronics. However, transforming colloidal nanoparticles into high‐performance and flexible devices remains a challenge. For example, flexible films prepared by solution‐processed semiconducting nanocrystals are typically plagued by poor thermoelectric and electrical transport properties. Here, a highly scalable 3D conformal additive printing approach to directly convert solution‐processed 2D nanoplates and 1D nanorods into high‐performing flexible devices is reported. The flexible films printed using Sb 2 Te 3 nanoplates and subsequently sintered at 400 °C demonstrate exceptional thermoelectric power factor of 1.5 mW m −1 K −2 over a wide temperature range (350–550 K). By synergistically combining Sb 2 Te 3 2D nanoplates with Te 1D nanorods, the power factor of the flexible film reaches an unprecedented maximum value of 2.2 mW m −1 K −2 at 500 K, which is significantly higher than the best reported values for p‐type flexible thermoelectric films. A fully printed flexible generator device exhibits a competitive electrical power density of 7.65 mW cm −2 with a reasonably small temperature difference of 60 K. The versatile printing method for directly transforming nanoscale building blocks into functional devices paves the way for developing not only flexible energy harvesters but also a broad range of flexible/wearable electronics and sensors.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Solution‐Processed CsPbBr 3 Quantum Dots/Organic Semiconductor Planar Heterojunctions for High‐Performance Photodetectors

Abstract Planar heterojunctions (PHJs) are fundamental building blocks for construction of semiconductor devices. However, fabricating PHJs with solution‐processable semiconductors such as organic semiconductors (OSCs) is a challenge. Herein, utilizing the orthogonal solubility and good wettability between CsPbBr 3 perovskite quantum dots (PQDs) and OSCs, fabrication of solution‐processed PQD/OSC PHJs are reported. The phototransistors based on bilayer PQD/PDVT‐10 PHJs show responsivity up to 1.64 × 10 4 A W −1 , specific detectivity of 3.17 × 10 12 Jones, and photosensitivity of 5.33 × 10 6 when illuminated by 450 nm light. Such high photodetection performance is attributed to efficient charge dissociation and transport, as well as the photogating effect in the PHJs. Furthermore, the tri‐layer PDVT‐10/PQD/Y6 PHJs are used to construct photodiodes working in self‐powered mode, which exhibit broad range photoresponse from ultraviolet to near‐infrared, with responsivity approaching 10 −1 A W −1 and detectivity over 10 6 Jones. These results present a convenient and scalable production processes for solution‐processed PHJs and show their great potential for optoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhancing Molecular Alignment and Charge Transport of Solution-Sheared Semiconducting Polymer Films by the Electrical-Blade Effect

Controlling polymer chain alignment through processing is a means of tuning the charge transport of solution-based conjugated polymers. In this work, a processing strategy is proposed in which an external electric field (E-field) is applied to the coating blade (E-blade) to align polymer chain during solution-shearing, a meniscus-guided coating technique. A theoretical model based on dielectrophoresis quantitatively describes and predicts the alignment process and is used to guide the selection of the optimal conditions of the applied E-field. Using these conditions, more than two-fold increase in chain alignment is observed for E-bladed thin films of a diketopyrrolopyrrole (DPP) semiconducting polymer without affecting other morphological aspects such as film thickness, film coverage or fiber-like aggregation. Organic field effect transistors based on the E-bladed DPP polymer are fabricated at ambient conditions and over areas of a few cm2. They display a 3-fold improvement in their mobilities and a strong enhancement in charge transport anisotropy compared to films prepared without E-field. These results reveal a synergistic alignment effect from both the solution-shearing process and the applied E-field, and introduce a novel and general approach to control the morphology and the electrical properties of solutioncoated conjugated polymer thin films.

42 ENGINEERING↗
DOE OSTI2017

Effect of Precursor Solution Aging on the Crystallinity and Photovoltaic Performance of Perovskite Solar Cells

Perovskite materials due to their exceptional photophysical properties are beginning to dominate the field of thin‐film optoelectronic devices. However, one of the primary challenges is the processing‐dependent variability in the properties, thus making it imperative to understand the origin of such variations. Here, it is discovered that the precursor solution aging time before it is cast into a thin film, is a subtle but a very important factor that dramatically affects the overall thin‐film formation and crystallinity and therein factors such as grain growth, phase purity, surface uniformity, trap state density, and overall solar cell performance. It is shown that progressive aging of the precursor promotes efficient formation of larger seeds after the fast nucleation of a large density of small seeds. The hot‐casting method then leads to the growth of large grains in uniform thin‐films with excellent crystallinity validated using scanning microscopy images and X‐ray diffraction patterns. The high‐quality films cast from aged solution is ideal for thin‐film photovoltaic device fabrication with reduced shunt current and good charge transport. This observation is a significant step toward achieving highly crystalline thin‐films with reliability in device performance and establishes the subtle but dramatic effect of solution aging before fabricating perovskite thin‐films.

Tsai, Hsinhan↗
DOE OSTI2019

Molecular Level Insight into Enhanced n‐Type Transport in Solution‐Printed Hybrid Thermoelectrics

Abstract Perylene diimide (PDI) derivatives hold great promise as stable, solution‐printable n‐type organic thermoelectric materials, but as of yet lack sufficient electrical conductivity to warrant further development. Hybrid PDI‐inorganic nanomaterials have the potential to leverage these physical advantages while simultaneously achieving higher thermoelectric performance. However, lack of molecular level insight precludes design of high performing PDI‐based hybrid thermoelectrics. Herein, the first explicit crystal structure of these materials is reported, providing previously inaccessible insight into the relationship between their structure and thermoelectric properties. Allowing this molecular level insight to drive novel methodologies, simple solution‐based techniques to prepare PDI hybrid thermoelectric inks with up to 20‐fold enhancement in thermoelectric power factor over the pristine molecule (up to 17.5 µW mK −2 ) is presented. This improved transport is associated with reorganization of organic molecules on the surface of inorganic nanostructures. Additionally, outstanding mechanical flexibility is demonstrated by fabricating solution‐printed thermoelectric modules with innovative folded geometries. This work provides the first direct evidence that packing/organization of organic molecules on inorganic nanosurfaces is the key to effective thermoelectric transport in nanohybrid systems.

Zaia, Edmond W.↗
DOE OSTI2021

Association‐based activity coefficient model for electrolyte solutions

Abstract This work presents an association‐based activity coefficient model that explicitly considers the solution nonideality due to associations among ions and solvent species. Built upon the electrolyte nonrandom two‐liquid (eNRTL) model, the model greatly improves the accuracy of eNRTL model for strongly associating electrolyte solutions due to presence of ionic species with high surface charge density. The model successfully correlates mean ionic activity coefficients of 46 aqueous single‐salt systems from 10 cations and 5 anions at 298.15 K up to their solubility limits. With the ion‐specific association parameters identified, the model accurately predicts activity and osmotic coefficients for aqueous mixed‐salt systems at 298.15 K. The temperature dependence of the model results has also been examined at 273–373 K. With superior accuracy over a wide range of concentration and temperature, the model represents a major advancement over eNRTL model and has a great potential to be a next‐generation model for electrolyte solutions.

Lin, Yu‐Jeng↗
DOE OSTI2021

A method to apply Zavitsas' aqueous electrolyte model to multicomponent solutions and its equivalence to Zdanovskii's rule

Abstract Zavitsas developed an aqueous electrolyte thermodynamic model and applied it to single electrolyte solutions previously. Here, a method to apply the model to multicomponent solutions is derived by setting the water activity to the mole fraction of free water in the mixture. The method is shown to work effectively for the CsBr‐KNO 3 ‐H 2 O and CsCl‐KNO 3 ‐H 2 O systems at 100.3°C even at concentrations greater than 6 molal. The largest error in the prediction of water activities was just −0.00365 for the CsBr‐KNO 3 ‐H 2 O system and −0.00631 for the CsCl‐KNO 3 ‐H 2 O system. Zavitsas' model naturally obeys Zdanovskii's rule because when two electrolyte solutions with the same fraction of free water are mixed together, water is obviously going to have that same fraction in the mixture. This means that Zavitsas' model will likely work well for the many electrolytes that obey Zdanovskii's rule.

Reynolds, Jacob G.↗
DOE OSTI2025

Flux Synthesis of Lattice‐Engineered Rutile Solid Solutions for Acidic Oxygen Evolution

Developing efficient and stable electrocatalysts for the acidic oxygen evolution reaction (OER) is vital for advancing proton exchange membrane water electrolysis (PEMWE) technologies. Here, in this study, we report a flux synthesis of nitrogen-doped Ti–Ru rutile-type solid-solution oxides (M-TiRu 4 ) using molten NaNO 3 as the flux medium. The flux medium promotes the low-temperature conversion of TiN to rutile TiO 2 , while in situ-formed RuO 2 nanoparticles facilitate lattice templating and couple with interfacial ion migration, enabling the formation of homogeneous solid solutions with abundant lattice heterogeneity. Simultaneously, nitrogen atoms are stably incorporated into the lattice of solid solutions, inducing bandgap narrowing, which enhances electronic conductivity. The developed M-TiRu 4 catalyst exhibits exceptional acidic OER performance, delivering a low overpotential of 194 mV at 10 mA cm −2 , superior durability over 600 h, and a Ru mass activity 7.8 times that of commercial RuO 2 . At the device level, M-TiRu 4 enables PEMWE operation at 1.64 V @ 2 A cm −2 and maintains stable performance at 500 mA cm −2 for 200 h with a minimal degradation rate of 20 µV h −1 . This work demonstrates a robust approach for designing high-performance, durable acidic OER catalysts via synergistic lattice and electronic structure engineering, paving the way for next-generation water-splitting technologies.

Wang, Fan [Univ. of Tennessee, Knoxville, TN (Unit↗
DOE OSTI2017

Guanidinium Group Remains Protonated in a Strongly Basic Arginine Solution

Knowledge of the acid dissociation constant of an amino acid has very important ramifications in the biochemistry of proteins and lipid bilayers in aqueous environments because charge and proton transfer depend on its value. The acid dissociation constant for the guanidinium group in arginine has historically been posited as 12.5, but there is substantial variation in published values over the years. Recent experiments suggest that the dissociation constant for arginine is much higher than 12.5, which explains why the arginine guanidinium group retains its positive charge under all physiological conditions. Here, we use X-ray photoelectron spectroscopy to study unsupported, aqueous arginine nanoparticles. By varying the pH of the constituent solution, we provide evidence that the guanidinium group is protonated even in a very basic solution. By analyzing the energy shifts in the C and N X-ray photoelectron spectra, we establish a molecular level picture of how charge and proton transport in aqueous solutions of arginine occur.

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

The shape of protein–polymer conjugates in dilute solution

ABSTRACT Protein–polymer conjugation can significantly affect many different aspects of protein behavior, ranging from their solution properties to their ability to form solution and bulk nanostructured materials. An underlying fundamental question is how the molecular design affects the shape of the conjugate and, consequently, its properties. This work measures the molecular configuration of model protein–polymer conjugates in dilute solution using small‐angle neutron scattering (SANS) and uses quantitative model fitting to understand the shape of the molecules. Form factor measurements of four model bioconjugates of the red fluorescent protein mCherry and the polymers poly( N ‐isopropylacrylamide), poly(hydroxypropyl acrylate), poly(oligoethylene glycol acrylate), and poly(ethylene glycol) show that these protein–polymer conjugates are well described by a recently developed scattering function for colloid–polymer conjugates that explicitly incorporates excluded volume interactions in the polymer configuration. In the regime where the protein does not exhibit strong interactions with the polymer, modeling the protein–polymer interactions using a purely repulsive Weeks–Chandler–Andersen potential also leads to a coarse‐grained depiction of the conjugate that agrees well with its scattering behavior. The coarse‐grained model can additionally be used for systems with varying protein–polymer interactions, ranging from purely repulsive to strongly attractive, which may be useful for conjugates with strong electrostatic or hydrophobic attractive interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 292–302

Lam, Christopher N.↗
DOE OSTI2016

Aerosol indirect effects on glaciated clouds. Part 2: Sensitivity tests using solute aerosols

Sensitivity tests were performed on a midlatitude continental case using a state‐of‐the‐art aerosol–cloud model to determine the salient mechanisms of aerosol indirect effects (AIE) from solute aerosols. The simulations showed that increased solute aerosols doubled cloud‐droplet number concentrations and hence reduced cloud particle sizes by about 20% and consequently inhibited warm rain processes, thus enhancing the chances of homogeneous freezing of cloud droplets and aerosols. Cloud fractions and their optical thicknesses increased quite substantially with increasing solute aerosols. Although liquid mixing ratios were boosted, there was, however, a substantial reduction of ice mixing ratios in the upper troposphere, owing to the increase in snow production aloft. The predicted total aerosol indirect effect was equal to −9.46 ± 1.4 W m −2 . The AIEs of glaciated clouds (−6.33 ± 0.95 W m −2 ) were greater than those of water‐only clouds (−3.13 ± 0.47 W m −2 ) by a factor of two in this continental case. The higher radiative importance of glaciated clouds compared with water‐only clouds emerged from their larger collective spatial extent and their existence above water‐only clouds. In addition to the traditional AIEs (glaciation, riming and thermodynamic), the new AIEs sedimentation, aggregation and coalescence were identified.

Kudzotsa, Innocent↗
DOE OSTI2021

Biosorption of copper from aqueous solutions utilizing agricultural wastes

Abstract The purpose of this study was to determine the copper (Cu) biosorption capacities of several agricultural wastes from aqueous solutions. Samples of agricultural wastes were tested unaltered and after hydrochloric acid (HCl) treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the Cu solutions. Desorption studies were performed to determine if the removed Cu could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional Cu biosorption cycles. The results of this study demonstrate a wide range of Cu biosorption proficiencies ranging from 0% to 100% removal. The parameters that resulted in higher Cu removal include higher pH and lower Cu solution concentration. Desorption results showed a 58% to 86% Cu recovery rate. Three of the five reused AWS were effective at removing Cu during subsequent trials. Therefore, these AWS types can be reused for additional Cu biosorption cycles. Hence, it is possible that using those AWS for metal treatment could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each Cu biosorption cycle.

Rizzuti, Anthony M.↗
DOE OSTI2017

Photoluminescence Enhancement of CuInS 2 Quantum Dots in Solution Coupled to Plasmonic Gold Nanocup Array

A strong plasmonic enhancement of photoluminescence (PL) decay rate in quantum dots (QDs) coupled to an array of gold-coated nanocups is demonstrated. CuInS2 QDs that emit at a wavelength that overlaps with the extraordinary optical transmission (EOT) of the gold nanocup array are placed in the cups as solutions. Time-resolved PL reveals that the decay rate of the QDs in the plasmonically coupled system can be enhanced by more than an order of magnitude. Using finite-difference time-domain (FDTD) simulations, it is shown that this enhancement in PL decay rate results from an enhancement factor of ≈100 in electric field intensity provided by the plasmonic mode of the nanocup array, which is also responsible for the EOT. The simulated Purcell factor approaches 86 at the bottom of the nanocup and is ≈3–15 averaged over the nanocup cavity height, agreeing with the experimental enhancement result. In conclusion, this demonstration of solution-based coupling between QDs and gold nanocups opens up new possibilities for applications that would benefit from a solution environment such as biosensing.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Type IIB supergravity solutions with AdS 5 from Abelian and non-Abelian T dualities

Here, we present a large class of new backgrounds that are solutions of type IIB supergravity with a warped AdS 5 factor, non-trivial axion-dilaton, B-field and three-form Ramond-Ramond flux but yet have no five-form flux. We obtain these solutions and many of their variations by judiciously applying non-Abelian and Abelian T-dualities, as well as coordinate shifts to AdS 5 × X 5 IIB supergravity solutions with X 5 = S 5 , T 1,1 , Y p,q . We address a number of issues pertaining to charge quantization in the context of non-Abelian T-duality. We comment on some properties of the expected dual super conformal field theories by studying their CFT central charge holographically. We also use the structure of the supergravity Page charges, central charges and some probe branes to infer aspects of the dual super conformal field theories.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Asymptotically-flat supergravity solutions deep inside the black-hole regime

Here we construct an infinite family of smooth asymptotically-flat supergravity solutions that have the same charges and angular momenta as general supersymmetric D1-D5-P black holes, but have no horizon. These solutions resemble the corresponding black hole to arbitrary accuracy outside of the horizon: they have asymptotically flat regions, AdS 3 ×S 3 throats and very-near-horizon AdS2 throats, which however end in a smooth cap rather than an event horizon. The angular momenta of the solutions are general, and in particular can take arbitrarily small values. Upon taking the AdS 3 ×S 3 decoupling limit, we identify the holographically-dual CFT states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

AdS 8 solutions in type II supergravity

We find non-supersymmetric AdS$_8$ solutions of type IIA supergravity. The internal space is topologically an $S^2$ with a U(1) isometry. The only non-zero flux is $F_0$; an O8 sourcing it is present at the equator of the $S^2$. The warping function and dilaton are non-constant. It is also possible to add D8-branes on top of the O8. Possible destabilizing brane bubbles (whose presence would be suggested by the weak-gravity conjecture) are either absent or collapsing. Our solutions are candidate holographic duals to unitary interacting CFTs in seven dimensions with exceptional global symmetry. We also present analogous non-supersymmetric AdS$_{d}$ solutions for general $d$ which are supported only by $F_0$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Scaling similarities and quasinormal modes of D0 black hole solutions

We study the gravity solution dual to the D0 brane quantum mechanics, or BFSS matrix model, in the ’t Hooft limit. The classical physics described by this gravity solution is invariant under a scaling transformation, which changes the action with a specific critical exponent, sometimes called the hyperscaling violating exponent. We present an argument for this critical exponent from the matrix model side, which leads to an explanation for the peculiar temperature dependence of the entropy in this theory, S ∝ T 9/5 . We also present a similar argument for all other Dp-brane geometries. We then compute the black hole quasinormal modes. This involves perturbing the finite temperature geometry. These perturbations can be easily obtained by a mathematical trick where we view the solution as the dimensional reduction of an Ad S2+9/5 × S 8 geometry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Reduction of Plutonium in Acidic Solutions by Mesoporous Carbons

Batch contact experiments with several porous carbon materials showed that carbon solids spontaneously reduce the oxidation state of plutonium in 1-1.5 M acid solutions, without significant adsorption. The final oxidation state and rate of Pu reduction varies with the solution matrix, and also depends on the surface chemistry and surface area of the carbon. It was demonstrated that acidic Pu(VI) solutions can be reduced to Pu(III) by passing through a column of porous carbon particles, offering an easy alternative to electrolysis with a potentiostat.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗