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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Advanced Nanocarbons for Enhanced Performance and Durability of Platinum Catalysts in Proton Exchange Membrane Fuel Cells

Insufficient stability of current carbon supported Pt and Pt alloy catalysts is a significant barrier for proton-exchange membrane fuel cells (PEMFCs). As a primary degradation cause to trigger Pt nanoparticle migration, dissolution, and aggregation, carbon corrosion remains a significant challenge. Compared with enhancing Pt and PtM alloy particle stability, improving support stability is rather challenging due to carbon's thermodynamic instability under fuel cell operation. In recent years, significant efforts have been made to develop highly durable carbon-based supports concerning innovative nanostructure design and synthesis along with mechanistic understanding. Here, this review critically discusses recent progress in developing carbon-based materials for Pt catalysts and provides synthesis–structure–performance correlations to elucidate underlying stability enhancement mechanisms. The mechanisms and impacts of carbon support degradation on Pt catalyst performance are first discussed. The general strategies are summarized to tailor the carbon structures and strengthen the metal–support interactions, followed by discussions on how these designs lead to enhanced support stability. Based on current experimental and theoretical studies, the critical features of carbon supports are analyzed concerning their impacts on the performance and durability of Pt catalysts in fuel cells. Finally, the perspectives are shared on future directions to develop advanced carbon materials with favorable morphologies and nanostructures to increase Pt utilization, strengthen metal-support interactions, facilitate mass/charge transfer, and enhance corrosion resistance.

25 ENERGY STORAGE↗
DOE OSTI2019

Cooling Induced Surface Reconstruction during Synthesis of High-Ni Layered Oxides

Transition metal layered oxides have been the dominant cathodes in lithium-ion batteries, and among them, high-Ni ones (LiNi x Mn y Co z O 2 ; x ≥ 0.7) with greatly boosted capacity and reduced cost are of particular interest for large-scale applications. The high Ni loading, on the other hand, raises the concern of surface instability and poor rate performance. The rational design of synthesis leading to layered LiNi 0.7 Mn 0.15 Co 0.15 O 2 with greatly enhanced rate capability is reflected, by implementing a quenching process alternative to the general slow cooling. In situ synchrotron X-ray diffraction, coupled with surface analysis, is applied to studies of the synthesis process, revealing cooling-induced surface reconstruction involving Li 2 CO 3 accumulation, formation of a Li-deficient layer and Ni reduction at the particle surface. The reconstruction process happens predominantly at high temperatures (above 350 °C) and is highly cooling-rate dependent, implying that surface reconstruction can be suppressed through synthetic control, i.e., quenching to improve the surface stability and rate performance of the synthesized materials. These findings may provide guidance to rational synthesis of high-Ni cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2014

Design of gem -Difluoro- bis -Tetrahydrofuran as P2 Ligand for HIV-1 Protease Inhibitors to Improve Brain Penetration: Synthesis, X-ray Studies, and Biological Evaluation

The structure–based design, synthesis, biological evaluation, and X–ray structural studies of fluorine–containing HIV–1 protease inhibitors are described. The synthesis of both enantiomers of the gem–difluoro–bis–THF ligands was carried out in a stereoselective manner using a Reformatskii–Claisen reaction as the key step. Optically active ligands were converted into protease inhibitors. Two of these inhibitors, (3R,3aS,6aS)–4,4–difluorohexahydrofuro[2,3–b]furan–3–yl(2S,3R)–3–hydroxy–4–((N–isobutyl–4–methoxyphenyl)sulfonamido)–1–phenylbutan–2–yl) carbamate (3) and (3R,3aS,6aS)–4,4–difluorohexahydrofuro[2,3–b]furan–3–yl(2S,3R)–3–hydroxy–4–((N–isobutyl–4–aminophenyl)sulfonamido)phenylbutan–2–yl) carbamate (4), exhibited HIV–1 protease inhibitory K i values in the picomolar range. Both 3 and 4 showed very potent antiviral activity, with respective EC 50 values of 0.8 and 3.1 nM against the laboratory strain HIV–1 LAI . The two inhibitors exhibited better lipophilicity profiles than darunavir, and also showed much improved blood–brain barrier permeability in an in vitro model. A high–resolution X–ray structure of inhibitor 4 in complex with HIV–1 protease was determined, revealing that the fluorinated ligand makes extensive interactions with the S2 subsite of HIV–1 protease, including hydrogen bonding interactions with the protease backbone atoms. Moreover, both fluorine atoms on the bis–THF ligand formed strong interactions with the flap Gly 48 carbonyl oxygen atom.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Design principles for hydrogen evolution reaction catalyst materials

Design and synthesis of active, stable and cost-effective materials for efficient hydrogen production (hydrogen evolution reaction, HER) is of paramount importance for the successful deployment of hydrogen -based alternative energy technologies. The HER, seemingly one of the simplest electrochemical reactions, has served for decades to bridge the gap between fundamental electrocatalysis and practical catalyst design. However, there are still many open questions that need to be answered before it would be possible to claim that design principles of catalyst materials are fully developed for the efficient hydrogen production. Here in this review, by summarizing key results for the HER on well-characterized electrochemical interfaces in acidic and alkaline media, we have broadened our understanding of the HER in the whole range of pH by considering three main parameters: the nature of the proton donor (H 3 O + in acid and H 2 O in alkaline), the energy of adsorption of H ad and OH ad , and the presence of spectator species. Simply by considering these three parameters we show that great deal has already been learned and new trends are beginning to emerge, giving some predictive ability with respect to the nature of electrochemical interface and electrocatalytic activity of the HER.

08 HYDROGEN↗
DOE OSTI2016

Versatile Thermochromic Supramolecular Materials Based on Competing Charge Transfer Interactions

Stimuli‐responsive supramolecular materials are of paramount importance for a broad range of applications. It is essential to impart versatility, sustainability, and scalability into these materials. Herein the authors report the design and synthesis of a new class of thermochromic supramolecular materials, which can easily be processed from water via a reversible sol–gel transition. The supramolecular materials are composed of a bis‐bipyridinium acceptor, a π‐electron‐rich naphthalene derivative donor, and halogen counterions. Long helical nanofibers can be assembled in water, gelating at room temperature. Inked designs, thin films, and aerogels are solution‐processed to exhibit thermochromic behavior based on competing π → π* and n → π* charge transfer interactions. By using different π‐electron rich donors, and counterions, the authors demonstrate that both the color observed at room temperature and at high temperatures can be tailored. The results open up the door to develop novel amphiphile‐based thermochromes with water processability and a large tunable color palette.

Yuan, Tianyu↗
DOE OSTI2016

Continuous injection synthesis of indium arsenide quantum dots emissive in the short-wavelength infrared

With the emergence of applications based on short-wavelength infrared light, indium arsenide quantum dots are promising candidates to address existing shortcomings of other infrared-emissive nanomaterials. However, III–V quantum dots have historically struggled to match the high-quality optical properties of II–VI quantum dots. Here we present an extensive investigation of the kinetics that govern indium arsenide nanocrystal growth. Based on these insights, we design a synthesis of large indium arsenide quantum dots with narrow emission linewidths. We further synthesize indium arsenide-based core-shell-shell nanocrystals with quantum yields up to 82% and improved photo- and long-term storage stability. We then demonstrate non-invasive through-skull fluorescence imaging of the brain vasculature of murine models, and show that our probes exhibit 2–3 orders of magnitude higher quantum yields than commonly employed infrared emitters across the entire infrared camera sensitivity range. Finally, we anticipate that these probes will not only enable new biomedical imaging applications, but also improved infrared nanocrystal-LEDs and photon-upconversion technology.

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

A fast grain-growth mechanism revealed in nanocrystalline ceramic oxides

Grain growth issues in nanocrystalline ceramic oxides render their highly attractive properties practically unusable due to limited understanding of the underlying grain-growth mechanisms. Two conventional “slow” grain-growth mechanisms, i.e. curvature driven and grain-rotation driven, are shown to be thermally active, and the discovery of a “fast” disorder-driven mechanism is revealed using molecular dynamics simulation on nanocrystalline ceria, in conjunction with experimental observations. We show that this disorder mechanism drives the unexpected fast grain growth observed experimentally during synthesis and irradiation conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Insights into the structural effects of layered cathode materials for high voltage sodium-ion batteries

Cathode materials are critical to the energy density, power density and safety of sodium-ion batteries (SIBs). Herein, we performed a comprehensive study to elucidate and exemplify the interplay mechanism between phase structures, interfacial microstrain and electrochemical properties of layered-structured Na x Ni 1/3 Co 1/3 Mn 1/3 O 2 cathode materials for high voltage SIBs. The electrochemical test results showed that Na x Ni 1/3 Co 1/3 Mn 1/3 O 2 with an intergrowth P2/O3/O1 structure demonstrates better electrochemical performance and better thermal stability than Na x Ni 1/3 Co 1/3 Mn 1/3 O 2 with P2/O3 binary-phase integration and Na x Ni 1/3 Co 1/3 Mn 1/3 O 2 where only the P phase is dominant. This result is caused by the distinct interfacial microstrain development during the synthesis and cycling of the P2/O3/O1 phase. In operando high energy X-ray diffraction further revealed that the intergrowth P2/O1/O3 cathode can inhibit the irreversible P2–O2 phase transformation and simultaneously improve the structure stability of the O3 and O1 phases during cycling. Here, we believe that interfacial microstrain can serve as an indispensable bridge to guide future design and synthesis of high performance SIB cathode materials and other high energy battery materials.

25 ENERGY STORAGE↗