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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Unraveling the Luminescence Quenching Mechanism in Strong and Weak Quantum-Confined CsPbBr 3 Triggered by Triarylamine-Based Hole Transport Layers

Luminescence quenching by hole transport layers (HTLs) is one of the major issues in developing efficient perovskite light-emitting diodes (PeLEDs), particularly prominent in blue-emitting devices. While a variety of material systems have been used as interfacial layers, the origin of such quenching and the type of interactions between perovskites and HTLs are still ambiguous. Here, we present a systematic investigation of the luminescence quenching of CsPbBr 3 by a commonly employed hole transport polymer, Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB) in LEDs. Strong and weakly quantum-confined CsPbBr 3 (nanoplatelets (NPLs)/nanocrystals (NCs)) are rationally selected to study the quenching mechanism by considering the differences in their morphology, energy level alignments, and quantum confinement. The steady-state and time-resolved Stern-Volmer plots unravel the dominance of dynamic and static quenching at lower and higher concentrations of TFB, respectively, with maximum quenching efficiency of 98%. The quenching rate in NCs is faster than in NPLs owing to their longer PL lifetimes and weak quantum confinement. The ultrafast transient absorption results support these dynamics and rule out the involvement of Forster or Dexter energy transfer. Finally, the 1D 1 H and 2D NOESY NMR study confirms the exchange of native ligands at the NCs surface with TFB, leading to dark CsPbBr 3 -TFB ensemble formation accountable for luminescence quenching. This highlights the critical role of the triarylamine functional group on TFB (also the backbone of many HTLs) in the quenching process. These results shed light on the underlying reasons for the luminescence quenching in PeLEDs and will help to choose the interfacial layers rationally for developing efficient LEDs.

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

Gain roll-off in cadmium selenide colloidal quantum wells under intense optical excitation

Colloidal quantum wells, or nanoplatelets, show among the lowest thresholds for amplified spontaneous emission and lasing among solution-cast materials and among the highest modal gains of any known materials. Using solution measurements of colloidal quantum wells, this work shows that under photoexcitation, optical gain increases with pump fluence before rolling off due to broad photoinduced absorption at energies lower than the band gap. Despite the common occurrence of gain induced by an electron–hole plasma found in bulk materials and epitaxial quantum wells, under no measurement conditions was the excitonic absorption of the colloidal quantum wells extinguished and gain arising from a plasma observed. Instead, like gain, excitonic absorption reaches a minimum intensity near a photoinduced carrier sheet density of 2 × 10 13 cm –2 above which the absorption peak begins to recover. To understand the origins of these saturation and reversal effects, measurements were performed with different excitation energies, which deposit differing amounts of excess energy above the band gap. Across many samples, it was consistently observed that less energetic excitation results in stronger excitonic bleaching and gain for a given carrier density. Transient and static optical measurements at elevated temperatures, as well as transient X-ray diffraction of the samples, suggest that the origin of gain saturation and reversal is a heating and disordering of the colloidal quantum wells which produces sub-gap photoinduced absorption.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Expanding the color palette of bicolor-emitting nanocrystals

Owing to their bright and tunable luminescence spectra, nanocrystals appear as a unique playground for light source design. Displays and lighting require white light sources that combine several narrow lines. As Kasha's rule prevents the emission of hot carriers, blends of multiple nanocrystal populations are currently the obvious strategy for broad-band source design. However, a few reports suggest that bicolor emission can also be obtained from a single particle even under weak excitation if a careful design of the exciton scattering mechanism sufficiently slows down its relaxation pathways. A key challenge remains to maintain quantum confinement for color tunability in the same structure, while simultaneously achieving a large size to leverage the critical, slower exciton diffusion or relaxation down to the ground state. In this work, we demonstrate that 2D nanoplatelets offer an original opportunity for the design of confined and large heterostructures. We demonstrate that bicolor emission is not limited to green–red pair and show that blue–yellow and purple–green emissions can be obtained from CdSe/CdTe/CdSe core/crown/crown and CdSe/CdS core/crown heterostructures, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Ion dynamics in hexagonal boron nitride ionogel electrolytes

Ionogel electrolytes incorporating exfoliated hexagonal boron nitride (hBN) nanoplatelets are promising materials for next-generation energy storage systems. However, detailed understanding of their ion transport properties at the molecular level remains limited. This study employs diffusion and relaxation nuclear magnetic resonance (NMR) techniques, including fast-field cycling (FFC) NMR, to investigate the dynamics of ionic species in hBN-ionogels. By spanning a broad frequency range from 30 kHz using FFC NMR to high-field NMR (500–800 MHz), we reveal distinct relaxation mechanisms governing ion dynamics in ionogels with and without lithium salts. Our results highlight the role of hBN in modulating molecular rotation and translational motion, significantly affecting 1 H and 19 F relaxation profiles. The presence of Li + alters the dynamic behavior in ionogels, enhancing anion mobility at the interface. Notably, 7 Li relaxation reveals strong interactions with the hBN surface that cannot be detected by diffusion NMR. Furthermore, these findings underscore the importance of spanning a broad frequency range in NMR studies of ionogels and provide critical insights into optimizing their design as novel electrolytes.

Electrolytes↗
DOE OSTI2021

Engineering Graphene-Ceramic 3D Composite Foams by Freeze Drying

A 3D graphene foam produced by the chemical vapor deposition (CVD) technique is recognized as an effective nanofiller material, as it does not agglomerate in the matrix. Though CVD facilitates pristine graphene foam production, the method poses limitations in developing large-scale 3D graphene composite foams as advanced engineering materials. In this paper, a freeze-drying (FD) process is used to produce a composite 3D foam, which is a mixture of graphene nanoplatelet (GNP) and a low-temperature co-fired ceramic (LTCC). The freeze-dried GNP-LTCC reticulated 3D composite foam has an average pore size ranging from 70 to 100 μm. Pore size is varied by regulating the heat transfer rate during the freezing process using a thermally conductive aluminum (Al) mold and a thermally insulating acrylonitrile butadiene styrene (ABS) mold. Computational thermal modeling is used to visualize the heat transfer and its effect on foam pore size. Subsequently, a freeze-dried GNP-LTCC composite foam is embedded into the LTCC matrix to form a hierarchical assembly by a spark plasma technique without compromising the 3D structure of the FD foam. This study established that a simple, eco-friendly, and scalable processing methodology can produce advanced graphene-based 3D composite foams as the future tailorable nanofillers for designing multimatrix materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

CsPbI 3 Nanocrystals Go with the Flow: From Formation Mechanism to Continuous Nanomanufacturing

Despite the groundbreaking advancements in the synthesis of inorganic lead halide perovskite (LHP) nanocrystals (NCs), stimulated from their intriguing size-, composition-, and morphology-dependent optical and optoelectronic properties, their formation mechanism through the hot-injection (HI) synthetic route is not well-understood. Here in this work, for the first time, in-flow HI synthesis of cesium lead iodide (CsPbI 3 ) NCs is introduced and a comprehensive understanding of the interdependent competing reaction parameters controlling the NC morphology (nanocube vs nanoplatelet) and properties is provided. Utilizing the developed flow synthesis strategy, a change in the CsPbI 3 NC formation mechanism at temperatures higher than 150 °C, resulting in different CsPbI 3 morphologies is revealed. Through comparison of the flow- versus flask-based synthesis, deficiencies of batch reactors in reproducible and scalable synthesis of CsPbI 3 NCs with fast formation kinetics are demonstrated. The developed modular flow chemistry route provides a new frontier for high-temperature studies of solution-processed LHP NCs and enables their consistent and reliable continuous nanomanufacturing for next-generation energy technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Layered Heterostructure Ionogel Electrolytes for High‐Performance Solid‐State Lithium‐Ion Batteries

Abstract Ionogel electrolytes based on ionic liquids and gelling matrices offer several advantages for solid‐state lithium‐ion batteries, including nonflammability, wide processing compatibility, and favorable electrochemical and thermal properties. However, the absence of ionic liquids that are concurrently stable at low and high potentials constrains the electrochemical windows of ionogel electrolytes and thus their high‐energy‐density applications. Here, ionogel electrolytes with a layered heterostructure are introduced, combining high‐potential (anodic stability: >5 V vs Li/Li + ) and low‐potential (cathodic stability: <0 V vs Li/Li + ) imidazolium ionic liquids in a hexagonal boron nitride nanoplatelet matrix. These layered heterostructure ionogel electrolytes lead to extended electrochemical windows, while preserving high ionic conductivity (>1 mS cm −1 at room temperature). Using the layered heterostructure ionogel electrolytes, full‐cell solid‐state lithium‐ion batteries with a nickel manganese cobalt oxide cathode and a graphite anode are demonstrated, exhibiting voltages that are unachievable with either the high‐potential or low‐potential ionic liquid alone. Compared to ionogel electrolytes based on mixed ionic liquids, the layered heterostructure ionogel electrolytes enable higher stability operation of full‐cell lithium‐ion batteries, resulting in significantly enhanced cycling performance.

Hyun, Woo Jin↗
DOE OSTI2023

Synthesis of Zwitterionic CsPbBr 3 Nanocrystals with Controlled Anisotropy using Surface‐Selective Ligand Pairs

Abstract Mechanistic studies of the morphology of lead halide perovskite nanocrystals (LHP‐NCs) are hampered by a lack of generalizable suitable synthetic strategies and ligand systems. Here, the synthesis of zwitterionic CsPbBr 3 NCs is presented with controlled anisotropy using a proposed “surface‐selective ligand pairs” strategy. Such a strategy provides a platform to systematically study the binding affinity of capping ligand pairs and the resulting LHP morphologies. By using zwitterionic ligands (ZwL) with varying structures, majority ZwL‐capped LHP NCs with controlled morphology are obtained, including anisotropic nanoplatelets and nanorods, for the first time. Combining experiments with density functional theory calculations, factors that govern the ligand binding on the different surface facets of LHP‐NCs are revealed, including the steric bulkiness of the ligand, the number of binding sites, and the charge distance between binding moieties. This study provides guidance for the further exploration of anisotropic LHP‐NCs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nematic Order, Plasmonic Switching and Self-Patterning of Colloidal Gold Bipyramids

Dispersing inorganic colloidal nanoparticles within nematic liquid crystals provides a versatile platform both for forming new soft matter phases and for predefining physical behavior through mesoscale molecular-colloidal self-organization. However, owing to formation of particle-induced singular defects and complex elasticity-mediated interactions, this approach has been implemented mainly just for colloidal nanorods and nanoplatelets, limiting its potential technological utility. Here, orientationally ordered nematic colloidal dispersions are reported of pentagonal gold bipyramids that exhibit narrow but controlled polarization-dependent surface plasmon resonance spectra and facile electric switching. Bipyramids tend to orient with their C 5 rotation symmetry axes along the nematic director, exhibiting spatially homogeneous density within aligned samples. Topological solitons, like heliknotons, allow for spatial reorganization of these nanoparticles according to elastic free energy density within their micrometer-scale structures. With the nanoparticle orientations slaved to the nematic director and being switched by low voltages ≈1 V within a fraction of a second, these plasmonic composite materials are of interest for technological uses like color filters and plasmonic polarizers, as well as may lead to the development of unusual nematic phases, like pentatic liquid crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Scalable Upcycling of Spent Lithium-Ion Battery Anodic Graphite to Electronic-Grade Graphene

Recycling processes for lithium-ion batteries (LIBs) are imperative to support the sustainable growth of global energy storage systems. This study introduces a scalable method for the upcycling of spent graphite anodes from LIBs to produce electronic-grade graphene nanoplatelets. In addition to comprehensive materials characterization, the electronic quality of the upcycled graphene is demonstrated by formulating it into a screen printing ink that achieves high-resolution patterning and thin-film electrical conductivity exceeding 104 S m−1. This screen printing ink is also used to print planar micro-supercapacitors with exceptional areal capacitance (1.78 mF cm−2), areal energy density (0.247 µWh cm−2), and cycling stability (> 10 000 cycles). Life cycle assessment (LCA) and techno-economic analysis (TEA) highlight the environmental benefits and cost reductions attainable through upcycling of graphite from LIBs. By capturing economic value from spent LIBs, this work fosters a sustainable battery supply chain and provides an abundant and geographically distributed raw material for electronic-grade graphene.

energy storage↗
DOE OSTI2024

Low‐Temperature and High‐Rate Rechargeable Aluminum Batteries Enabled by Ternary Eutectic Electrolytes

Abstract Rechargeable aluminum batteries (RABs) have garnered extensive scientific attention as a promising alternative chemistry due to the inherent advantages associated with aluminum (Al) metal anodes, including their high theoretical capacities, cost‐effectiveness, environmental friendliness, and inherent non‐flammable properties. Nonetheless, the practical energy density of RABs is constrained by the electrolytes that support lower operational voltage windows. Herein, we report a ternary eutectic electrolyte composed of 1‐ethyl‐3‐methylimidazolium chloride ([C 2 C 1 im]Cl):1‐butyl‐3‐methylimidazolium chloride ([C 4 C 1 im]Cl):aluminum chloride (AlCl 3 ) for the application of RABs. The electrolyte exhibits a high operational potential window (~3 V vs. Al/Al 3+ on SS 316) and high ionic conductivity (~8.3 mS cm −1 ) while exhibiting only a low temperature glass transition at −65 °C suitable for all‐climate conditions. Al||graphene nanoplatelets cell delivers a high capacity of ~117 mAh/g, and ~43 mAh/g at a very high current densities of 1 A/g and 5 A/g, respectively. The cells render a reversible capacity of 20 mAh/g at −20 °C and 17 mAh/g at −40 °C, indicating their suitability for operation under extreme environmental conditions. We comprehensively evaluated the design and optimization of carbon paper‐based battery systems. The ternary eutectic electrolyte demonstrates exceptional electrochemical performance, thus signifying its substantial potential for utilization in high‐performance energy storage systems in all climates.

Vadthya, Raju↗
DOE OSTI2022

Evaluating the Lightning Strike Damage Tolerance for CFRP Composite Laminates Containing Conductive Nanofillers

Conductive nanofillers, such as carbon nanotube, graphene nanoplatelets, and carbon black particles (with diameters in nanometers) have been shown to enhance the electrical conductivity of fiber reinforced polymer matrix composites in many existing studies. The motivation is primarily for lightning strike protection, electromagnetic interference shielding, de-icing, and the manufacturing of lightweight electronic components. Here, we evaluate the lightning strike damage tolerance of carbon fiber reinforced polymer (CFRP) matrix composite laminates containing conductive nanofillers with varying weight fractions, including carbon black (CB), carbon nanotubes (CNT), and a mix of CB and CNT, through simulated lightning strike tests, followed by both non-destructive ultrasonic inspection and destructive sectioning to characterize the damage inflicted by the simulated lightning strike. Three-point flexural tests are performed to evaluate the residual strength retained by all CFRP specimens. Results show that lightning strike damage experienced varying levels of reduction for CFRP composite specimens containing conductive fillers in comparison to the baseline specimen without fillers. Notably, the delamination only penetrated to the interface between the 1st and 2nd layer for the specimen with 0.25 wt.% CNT in comparison to the baseline CFRP specimen for which the delamination penetrated to the interface between the 5th and 6th layer. Moreover, the retention of the flexural modulus increased from 26.5% to a maximum of 95.0% for the specimen with 0.25 wt.% hybrid CB and CNT. Yet, we show that using our chosen conductive fillers cannot fully eliminate lightning strike damage. Additionally, adding conductive fillers could compromise the flexural properties. We provide discussions on future recommendations on using conductive fillers for the lightning strike protection of CFRP composites.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The first experimental evidence for improved nanomechanical properties of calcium silicate hydrate by polycarboxylate ether and graphene oxide

Graphene oxide (GO) efficiently enhances macroscale mechanical properties of cement-based materials. Yet the nanoscale reinforcing mechanism of GO for calcium silicate hydrate (C-S-H), the key binding phase of concrete, remains poorly understood. Moreover, how polycarboxylate ether (PCE)-based superplasticizers affect the nanomechanical properties of C-S-H remains unclear. The intrinsic mechanical properties of the nanocomposites are measured using high-pressure X-ray diffraction. The influences of GO and PCE on the local Ca and Si environments are probed using X-ray absorption spectroscopy. For the first time, we evidence that PCE-induced well-dispersed GO nanoplatelets strengthen the C-S-H basal planes, whereas poorly water-dispersed GO weakly interacts with basal planes and does not strengthen in plane Casingle bondO bonds. Both PCE and GO only slightly strengthen C-S-H's c-axis. Here, the bulk modulus of C-S-H/PCE/GO nanocomposite is 190% than pure C-S-H. Functional groups of PCE and GO prefer interacting with the Casingle bondO sheets of C-S-Hs instead of silicate tetrahedra.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Hierarchical low Pt-loading “core-shell” electrocatalysts for the oxygen reduction reaction in fuel cells

The sluggish kinetics of the oxygen reduction reaction (ORR) hinder cost-effective polymer electrolyte fuel cells (PEFCs), which rely on scarce, expensive platinum-based electrocatalysts (ECs). Here, we present a novel synthesis method for ORR ECs achieving exceptional platinum utilization. The design features a hierarchical “multi-carbon” support comprising carbon nanoparticles interacting with graphene nanoplatelets as the “core”, encapsulated by a porous carbon nitride (CN) “shell”. This configuration promotes strong core/shell interactions and a bimodal active site distribution, consisting of chemically dispersed Pt and Ni single-atom complexes and PtNix alloy nanoclusters embedded in the CN shell. These advantages enable high activity and durability, achieving an ORR activity of 1.6 A mgPt−1 at 0.9 V vs. RHE-an order of magnitude higher than Pt/C (0.17 A mgPt−1). A proof-of-concept PEFC demonstrates a specific power of 12.0 kW gPt−1 at 0.60 V. This approach offers a significant step toward more efficient and sustainable PEFC technologies.

Pagot, Gioele [University of Padova, Italy]↗
DOE OSTI2022

Enhanced thermoelectric performance of PbSe-graphene nanocomposite manufactured with acoustic cavitation induced defects

An order of magnitude rise in the thermoelectric (TE) performance of the PbSe, a scalable and easy-to-manufacture TE material, has been achieved by incorporating reduced graphene oxide (Gr) nanoplatelets in a PbSe/PbSeO 3 heterostructure formed by acoustic cavitation-assisted oxidation. The fabricated Gr/PbSe/PbSeO 3 nanocomposites exhibit high TE performance with an exceptionally high Seebeck coefficient coupled with low thermal conductivity. The variation in the Seebeck coefficient has been attributed to a reduction in charge carrier mobility due to the ferroelectric polarization effect. Furthermore, the increase in electrical resistivity is minimized by adding graphene. At an optimal weight fraction (0.2 wt%), graphene nano-inclusions lead to superior Seebeck coefficient values as high as ~2000 μV/K at ~500 K, providing high overall TE performance. This study shows substantial changes in the TE properties of PbSe through the incorporation of graphene and PbSeO 3 . The understanding and methodology developed in this study can be exploited for the scalable manufacturing of high-performance TE materials.

Structure-property correlations↗
DOE OSTI2021

The Surface Chemistry and Structure of Colloidal Lead Halide Perovskite Nanocrystals

Since the initial discovery of colloidal lead halide perovskite nanocrystals, there has been significant interest placed on these semiconductors because of their remarkable optoelectronic properties, including very high photoluminescence quantum yields, narrow size- and composition-tunable emission over a wide color gamut, defect tolerance, and suppressed blinking. These material attributes have made them attractive components for next-generation solar cells, light emitting diodes, low-threshold lasers, single photon emitters, and X-ray scintillators. While a great deal of research has gone into the various applications of colloidal lead halide perovskite nanocrystals, comparatively little work has focused on the fundamental surface chemistry of these materials. While the surface chemistry of colloidal semiconductor nanocrystals is generally affected by their particle morphology, surface stoichiometry, and organic ligands that contribute to the first coordination sphere of their surface atoms, these attributes are markedly different in lead halide perovskite nanocrystals because of their ionicity. Herein, emerging work on the surface chemistry of lead halide perovskite nanocrystals is highlighted, with a particular focus placed on the most-studied composition of CsPbBr 3 . We begin with an in-depth exploration of the native surface chemistry of as-prepared, 0-D cuboidal CsPbBr 3 nanocrystals, including an atomistic description of their surface termini, vacancies, and ionic bonding with ligands. We then proceed to discuss various post-synthetic surface treatments that have been developed to increase the photoluminescence quantum yields and stability of CsPbBr 3 nanocrystals, including the use of tetraalkylammonium bromides, metal bromides, zwitterions, and phosphonic acids, and how these various ligands are known to bind to the nanocrystal surface. To underscore the effect of post-synthetic surface treatments on the application of these materials, we focus on lead halide perovskite nanocrystal-based light emitting diodes, and the positive effect of various surface treatments on external quantum efficiencies. We also discuss the current state-of-the-art in the surface chemistry of 1-D nanowires and 2-D nanoplatelets of CsPbBr 3 , which are more quantum confined than the corresponding cuboidal nanocrystals but also generally possess a higher defect density because of their increased surface area-to-volume ratios.

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

Unraveling the Growth Mechanism of Strongly Confined CsPbBr 3 Perovskite Quantum Dots under Thermodynamic Equilibrium Control

Size-confined lead halide perovskite quantum dots (PQDs) are promising materials for optoelectronic devices. Large quantities of PQDs with high ensemble uniformity are often needed for device fabrication. The thermodynamic-equilibrium-controlled synthesis can produce PQDs with good size and shape uniformity. Unfortunately, scaling up this synthesis often produces unwanted perovskite nanoplatelets (NPLs). To date, the PQD and NPL growth mechanism under thermodynamic equilibrium control remains unexplored. We discovered that the growth of size-confined CsPbBr 3 PQDs is mediated by ultrasmall (~ 2.4 nm) metastable nanoclusters. These nanoclusters can eventually grow into PQDs when sufficient Cs-precursors are provided. Otherwise, the unreacted nanoclusters will self-assemble and fuse into NPLs during the synthesis and/or PQD purification. Furthermore, by controlling the homogeneous growth of nanoclusters, strongly confined (≤ 5 nm) PQDs with high size uniformity can be produced at the gram scale.

77 NANOSCIENCE AND NANOTECHNOLOGY↗