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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Impact of Weak Agostic Interactions in Nickel Electrocatalysts for Hydrogen Oxidation

To understand how H2 binding and oxidation is influenced by [Ni(PR2NR'2)2]2+ PR2NR'2 catalysts with H2 binding energies close to thermoneutral, two [Ni(PPh2NR'2)2]2+ (R = Me or C14H29) complexes with phenyl substituents on phosphorous and varying alkyl chain lengths on the pendant amine were studied. In the solid state, [Ni(PPh2NMe2)2]2+ exhibits an anagostic interaction between the Ni(II) center and the a-CH3 of the pendant amine, and DFT and variable-temperature 31P NMR experiments suggest than the anagostic interaction persists in solution. The equilibrium constants for H2 addition to these complexes was measured by 31P NMR spectroscopy, affording free energies of H2 addition (?G°H2) of –0.8 kcal mol–1 in benzonitrile and –1.6 to –2.3 kcal mol–1 in THF. The anagostic interaction contributes to the low driving force for H2 binding by stabilizing the four-coordinate Ni(II) species prior to binding of H2. The pseudo-first order rate constants for H2 addition at 1 atm were measured by variable scan rate cyclic voltammetry, and were found to be similar for both complexes, less than 0.2 s–1 in benzonitrile and 3 –6 s–1 in THF. In the presence of exogenous base and H2 , turnover frequencies of electrocatalytic H2 oxidation were measured to be less than 0.2 s–1 in benzonitrile and 4 –9 s–1 in THF. These complexes are slower electrocatalysts for H2 oxidation than previously studied [Ni(PR2NR'2)2]2+ complexes due to a competition between H2 binding and formation of the anagostic interaction. However, the decrease in catalytic rate is accompanied by a beneficial 130 mV decrease in overpotential. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences. Computational resources were provided at the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory. Mass spectrometry experiments were performed in the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located and the Pacific Northwest National Laboratory (PNNL). The authors thank Dr. Rosalie Chu for mass spectroscopy analysis. PNNL is operated by Battelle for DOE.

Klug, Christina↗
DOE OSTI2017

Tipping Point for Expansion of Layered Aluminosilicates in Weakly Polar Solvents: Supercritical CO2

Layered aluminosilicates play a dominant role in the mechanical and gas storage properties of the subsurface, are used in diverse industrial applications, and serve as model materials for understanding solvent-ion-support systems. Although expansion in the presence of H2O is well known to be systematically correlated with the hydration free energy of the interlayer cation, in environments dominated by non-polar solvents (i.e. CO2), uptake into the interlayer is not well-understood. Using novel high pressure capabilities, we investigated the interaction of super-critical CO2 with Na+-, NH4+-, and Cs+-saturated montmorillonite, comparing results with predictions from molecular dynamics simulations. Despite the known trend in H2O, and that cation solvation energies in CO2 suggest a stronger interaction with Na+, both the NH4+- and Cs+-clays readily absorbed CO2 and expanded while the Na+-clay did not. The apparent inertness of the Na+-clay was not due to kinetics, as experiments seeking a stable expanded state showed that none exists. Molecular dynamics simulations revealed a large endothermicity to CO2 intercalation in the Na+-clay, but little or no energy barrier for the NH4+- and Cs+-clays. Consequently, we have shown for the first time that in the presence of a low dielectric constant gas swelling depends more on the strength of the interaction between interlayer cation and aluminosilicate sheets and less on that with solvent. The finding suggests a distinct regime in layered aluminosilicates swelling behavior triggered by low solvent polarizability, with important implications in geomechanics, storage and retention of volatile gases, and across industrial uses in gelling, decoloring, heterogeneous catalysis, and semi-permeable reactive barriers.

CO2, montmorillonite, molecular dynamics↗
DOE OSTI2024

A weakly ion pairing electrolyte designed for high voltage magnesium batteries

High-voltage rechargeable magnesium batteries (RMBs) are potential alternatives to lithium-ion batteries owing to the low cost and high abundance of magnesium. However, the parasitic reactions of the latter with many electrolytes greatly hinders the stability and kinetics of Mg plating/stripping. Here we report a new and easily accessible solvent-designed electrolyte, which effectively solves the difficulty of ion pair dissociation and facilitates fast nanoscale Mg nucleation/growth using simple Mg(TFSI)2 as the salt, enabling a facile interfacial charge transfer process. Dendrite-free Mg plating/stripping is maintained for over 7000 hours (∼10 months) at a practical areal capacity of 2 mA h cm−2. The high-voltage stability of these electrolytes is demonstrated by benchmarking with polyaniline||Mg full cells with an operating voltage up to 3.5 V that exhibit stable cycling at a 2C rate with 99% coulombic efficiency after 400 cycles. This work opens up new frontiers in coupling low-cost electrolytes with next-generation high-voltage cathode materials for fast-charging RMBs with long life and high energy densities.

Li, Chang↗
DOE OSTI2017

Galaxy–Galaxy Weak-lensing Measurements from SDSS. I. Image Processing and Lensing Signals

We present our image processing pipeline that corrects the systematics introduced by the point-spread function (PSF). Using this pipeline, we processed Sloan Digital Sky Survey (SDSS) DR7 imaging data in r band and generated a galaxy catalog containing the shape information. Based on our shape measurements of the galaxy images from SDSS DR7, we extract the galaxy–galaxy (GG) lensing signals around foreground spectroscopic galaxies binned in different luminosities and stellar masses. We estimated the systematics, e.g., selection bias, PSF reconstruction bias, PSF dilution bias, shear responsivity bias, and noise rectification bias, which in total is between −9.1% and 20.8% at 2 σ levels. The overall GG lensing signals we measured are in good agreement with Mandelbaum et al. The reduced χ {sup 2} between the two measurements in different luminosity bins are from 0.43 to 0.83. Larger reduced χ {sup 2} from 0.60 to 1.87 are seen for different stellar mass bins, which is mainly caused by the different stellar mass estimator. The results in this paper with higher signal-to-noise ratio are due to the larger survey area than SDSS DR4, confirming that more luminous/massive galaxies bear stronger GG lensing signals. We divide the foreground galaxies into red/blue and star-forming/quenched subsamples and measure their GG lensing signals. We find that, at a specific stellar mass/luminosity, the red/quenched galaxies have stronger GG lensing signals than their counterparts, especially at large radii. These GG lensing signals can be used to probe the galaxy–halo mass relations and their environmental dependences in the halo occupation or conditional luminosity function framework.

79 ASTRONOMY AND ASTROPHYSICS↗