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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Increasing the rate of hydrogen oxidation without increasing the overpotential: A bio-inspired iron molecular electrocatalyst with an outer coordination sphere proton relay

Oxidation of hydrogen (H₂) to protons and electrons for energy production in fuel cells is catalyzed by platinum, but its low abundance and high cost present drawbacks to widespread adoption. Precisely controlled proton delivery and removal is critical in hydrogenase enzymes in nature that catalyze H₂ oxidation using earth-abundant metals (iron and nickel). Here we report a synthetic iron complex, (Cp C 5 F 4 N )Fe(P Et N (CH 2 ) 3 NMe 2 PEt)(Cl), that serves as a precatalyst for the oxidation of H₂, with turnover frequencies of 290 s⁻¹ in fluorobenzene, under 1 atm of H₂ using 1,4-diazabicyclo[2.2.2]octane (DABCO) as the exogenous base. The cooperative effect of the primary, secondary and outer coordination spheres for moving protons in this remarkably fast catalyst emphasizes the key role of pendant amines in mimicking the functionality of the proton pathway in the hydrogenase enzymes.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Cumulene Wires Display Increasing Conductance with Increasing Length

One-dimensional sp-hybridized carbon wires, including cumulenes and polyynes, can be regarded as finite versions of carbynes. They are likely to be good candidates for molecular-scale conducting wires as they are predicted to have a high-conductance. In this study, we first characterize the single-molecule conductance of a series of cumulenes and polyynes with a backbone ranging in length from 4 to 8 carbon atoms, including [7]cumulene, the longest cumulenic carbon wire studied to date for molecular electronics. We observe different length dependence of conductance when comparing these two forms of carbon wires. Polyynes exhibit conductance decays with increasing molecular length, while cumulenes show a conductance increase with increasing molecular length. Their distinct conducting behaviors are attributed to their different bond length alternation, which is supported by theoretical calculations. Furthermore, this study confirms the long-standing theoretical predictions on sp-hybridized carbon wires and demonstrates that cumulenes can form highly conducting molecular wires.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Increased light-use efficiency in northern terrestrial ecosystems indicated by CO 2 and greening observations: INCREASE IN NH LIGHT USE EFFICIENCY

Observations show an increasing amplitude in the seasonal cycle of CO2 (ASC) north of 45°N of 56 ± 9.8% over the last 50 years and an increase in vegetation greenness of 7.5–15% in high northern latitudes since the 1980s. However, the causes of these changes remain uncertain. Historical simulations from terrestrial biosphere models in the Multiscale Synthesis and Terrestrial Model Intercomparison Project are compared to the ASC and greenness observations, using the TM3 atmospheric transport model to translate surface fluxes into CO2 concentrations. We find that the modeled change in ASC is too small but the mean greening trend is generally captured. Modeled increases in greenness are primarily driven by warming, whereas ASC changes are primarily driven by increasing CO2. We suggest that increases in ecosystem-scale light use efficiency (LUE) have contributed to the observed ASC increase but are underestimated by current models. We highlight potential mechanisms that could increase modeled LUE.

Thomas, Rebecca T.↗
DOE OSTI2015

On the increased efficiency in InGaN-based multiple quantum wells emitting at 530–590 nm with AlGaN interlayers

InGaN/AlGaN/GaN-based multiple quantum wells (MQWs) with AlGaN interlayers (ILs) are investigated, specifically to examine the fundamental mechanisms behind their increased radiative efficiency at wavelengths of 530–590 nm. The Al z Ga 1-z N (z~0.38) IL is ~1–2 nm thick, and is grown after and at the same growth temperature as the ~3 nm thick InGaN quantum well (QW). This is followed by an increase in temperature for the growth of a ~10 nm thick GaN barrier layer. The insertion of the AlGaN IL within the MQW provides various benefits. First, the AlGaN IL allows for growth of the In x Ga 1-x N QW well below typical growth temperatures to achieve higher x (up to~0.25). Second, annealing the IL capped QW prior to the GaN barrier growth improves the AlGaN IL smoothness as determined by atomic force microscopy, improves the InGaN/AlGaN/GaN interface quality as determined from scanning transmission electron microscope images and x-ray diffraction, and increases the radiative efficiency by reducing non-radiative defects as determined by time-resolved photoluminescence measurements. Finally, the AlGaN IL increases the spontaneous and piezoelectric polarization induced electric fields acting on the InGaN QW, providing an additional red-shift to the emission wavelength as determined by Schrodinger-Poisson modeling and fitting to the experimental data. The relative impact of increased indium concentration and polarization fields on the radiative efficiency of MQWs with AlGaN ILs is also explored, along with implications to conventional longer wavelength emitters.

14 SOLAR ENERGY↗
DOE OSTI2014

Multifold Seebeck increase in RuO{sub 2} films by quantum-guided lanthanide dilute alloying

Ab initio predictions indicating that alloying RuO{sub 2} with La, Eu, or Lu can increase the Seebeck coefficient α manifold due to quantum confinement effects are validated in sputter-deposited La-alloyed RuO{sub 2} films showing fourfold α increase. Combinatorial screening reveals that α enhancement correlates with La-induced lattice distortion, which also decreases the thermal conductivity twentyfold, conducive for high thermoelectric figures of merit. These insights should facilitate the rational design of high efficiency oxide-based thermoelectrics through quantum-guided alloying.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Contribution of urbanization to the increase of extreme heat events in an urban agglomeration in east China

Abstract The urban agglomeration of Yangtze River Delta (YRD) is emblematic of China's rapid urbanization during the past decades. Based on homogenized daily maximum and minimum temperature data, the contributions of urbanization to trends of summer extreme temperature indices (ETIs) in YRD are evaluated. Dynamically classifying the observational stations into urban and rural, this study presents unexplored changes in temperature extremes during the past four decades in YRD and quantifies the amplification of the positive trends in ETIs by the urban heat island effect. Overall, urbanization contributes to more than one third of the increase of intensity of extreme heat events in the region, which is comparable to the contribution of greenhouse gases. Compared to rural stations, more notable shifts to the right in the probability distribution of temperature and ETIs are found in urban stations. The rapid urbanization in YRD has resulted in large increases in the risk of heat extremes.

Yang, Xuchao↗
DOE OSTI2015

Continuous motion scan ptychography: Characterization for increased speed in coherent x-ray imaging

Ptychography is a coherent diffraction imaging (CDI) method for extended objects in which diffraction patterns are acquired sequentially from overlapping coherent illumination spots. The object’s complex transmission function can be reconstructed from those diffraction patterns at a spatial resolution limited only by the scattering strength of the object and the detector geometry. Most experiments to date have positioned the illumination spots on the sample using a move-settle-measure sequence in which the move and settle steps can take longer to complete than the measure step. We describe here the use of a continuous “fly-scan” mode for ptychographic data collection in which the sample is moved continuously, so that the experiment resembles one of integrating the diffraction patterns from multiple probe positions. This allows one to use multiple probe mode reconstruction methods to obtain an image of the object and also of the illumination function. We show in simulations, and in x-ray imaging experiments, some of the characteristics of fly-scan ptychography, including a factor of 25 reduction in the data acquisition time. This approach will become increasingly important as brighter x-ray sources are developed, such as diffraction limited storage rings.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Increasing the Stability of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are a new category of advanced porous materials undergoing study by many researchers for their vast variety of both novel structures and potentially useful properties arising from them. Their high porosities, tunable structures, and convenient process of introducing both customizable functional groups and unsaturated metal centers have afforded excellent gas sorption and separation ability, catalytic activity, luminescent properties, and more. However, the robustness and reactivity of a given framework are largely dependent on its metal-ligand interactions, where the metal-containing clusters are often vulnerable to ligand substitution by water or other nucleophiles, meaning that the frameworks may collapse upon exposure even to moist air. Other frameworks may collapse upon thermal or vacuum treatment or simply over time. This instability limits the practical uses of many MOFs. In order to further enhance the stability of the framework, many different approaches, such as the utilization of high-valence metal ions or nitrogen-donor ligands, were recently investigated. This review details the efforts of both our research group and others to synthesize MOFs possessing drastically increased chemical and thermal stability, in addition to exemplary performance for catalysis, gas sorption, and separation.

Bosch, Mathieu↗
DOE OSTI2023

Simultaneous expression of an endogenous spermidine synthase and a butanol dehydrogenase from Thermoanaerobacter pseudethanolicus in Clostridium thermocellum results in increased resistance to acetic acid and furans, increased ethanol production and an increase in thermotolerance

Abstract Background Sensitivity to inhibitors derived from the pretreatment of plant biomass is a barrier to the consolidated bioprocessing of these complex substrates to fuels and chemicals by microbes. Spermidine is a low molecular weight aliphatic nitrogen compound ubiquitous in microorganisms, plants, and animals and is often associated with tolerance to stress. We recently showed that overexpression of the endogenous spermidine synthase enhanced tolerance of the Gram-positive bacterium, Clostridium thermocellum to the furan derivatives furfural and HMF. Results Here we show that co-expression with an NADPH-dependent heat-stable butanol dehydrogenase from Thermoanaerobacter pseudethanolicus further enhanced tolerance to furans and acetic acid and most strikingly resulted in an increase in thermotolerance at 65 °C. Conclusions Tolerance to fermentation inhibitors will facilitate the use of plant biomass substrates by thermophiles in general and this organism in particular. The ability to grow C. thermocellum at 65 °C has profound implications for metabolic engineering.

09 BIOMASS FUELS↗
DOE OSTI2018

Increasing methane emissions from natural land ecosystems due to sea-level rise

Because methane (CH4) is currently the second most important greenhouse gas, it is important to accurately quantify CH4 emissions from terrestrial ecosystems. Different from many current modelling studies which focus on how CH4 emissions respond to a variety of environmental factors in land ecosystems, we analyzed how methane emitted from lands responded to sea-level increase (SLR) in this study. To do so, a large-scale surface water routing module was incorporated into our existing CH4 model and we designed an efficient simulation protocol to capture small variations in inundation extent due to SLR. Both the annual maximum inundation extent and CH4 emissions showed a steadily growing trend, increasing 1.21 × 105 km2 and 3.13 Tg CH4 /yr globally, respectively, in a 22-year SLR experiment during 1993-2014. Most of new inundation and methane source areas were located near rivers’ deltas and along the downstream reaches of rivers. The increase in inundation extent is primarily influenced by precipitation, channel geomorphic characteristics and topography of riverside area. The growth of CH4 emissions due to the SLR is largely determined by inundation extent but other factors such as temperature and carbon storage also played the important roles. Although the current SLR-induced increases in inundation extent and CH4 emissions only accounted for 1.0% and 1.3% of their global totals, they took 7.0% and 17.3% of the mean annual variability in both, respectively, during the study period. Considering SLR has a long-term but stable increasing trend, future SLR under potential climate change could play a more important role in evaluating dynamic of CH4 emissions.

Lu, Xiaoliang↗
DOE OSTI2021

Chronic arsenic increases cell migration in BEAS-2B cells by increasing cell speed, cell persistence, and cell protrusion length

Highlights: • Chronic arsenic exposure primes lung epithelial cells for enhanced cell migration. • Chronic arsenic increases cell motility in an EGFR-dependent manner. • Chronic arsenic increases cell persistence in an EGFR-independent manner. • EGFR is sufficient, but not necessary for increasing cell protrusion length in chronic arsenic treated cells. There is a strong association between arsenic exposure and lung cancer development, however, the mechanism by which arsenic exposure leads to carcinogenesis is not clear. In our previous study, we observed that when BEAS-2B cells are chronically exposed to arsenic, there is an increase in secreted TGFα, as well as an increase in EGFR expression and activity. Further, these changes were broadly accompanied with an increase in cell migration. The overarching goal of this study was to acquire finer resolution of the arsenic-dependent changes in cell migration, as well as to understand the role of increased EGFR expression and activity levels in the underlying mechanisms of cell migration. To do this, we used a combination of biochemical and single cell assays, and observed chronic arsenic treatment enhancing cell migration by increasing cell speed, cell persistence and cell protrusion length. All three parameters were further increased by the addition of TGFα, indicating EGFR activity is sufficient to enhance those aspects of cell migration. In contrast, EGFR activity was necessary for the increase in cell speed, as it was reversed with an EGFR inhibitor, AG1478, but was not necessary to enhance persistence and protrusion length. From these data, we were able to isolate both EGFR-dependent and –independent features of cell migration that were enhanced by chronic arsenic exposure.

60 APPLIED LIFE SCIENCES↗