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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Iron Complexes Bearing Diphosphine Ligands with Positioned Pendant Amines as Electrocatalysts for the Oxidation of H2

The synthesis and spectroscopic characterization of CpC5F4NFe(PtBu2NBn2)Cl, [3-Cl] (where C5F4N is the tetrafluorpyridyl substituent and PtBu2NBn2 = 1,5-di(tert-butyl)-3,7-di(benzyl)-1,5-diaza-3,7-diphosphacyclooctane) are reported. Complex 3-Cl and previously reported [CpC5F4NFe(PtBu2NtBu2)Cl], 4-Cl, are precursors to intermediates in the catalytic oxidation of H2, including CpC5F4NFe(PtBu2NBn2)H (3-H), CpC5F4NFe(PtBu2NtBu2)H (4-H), [CpC5F4NFe(PtBu2NBn2)]BArF4 ([3](BArF4), [CpC5F4NFe(PtBu2NtBu2)]BArF4 ([4](BArF4), [CpC5F4NFe(PtBu2NBn2)(H2)]BArF4 ([3-H2]BArF4), and [CpC5F4NFe(PtBu2NtBu2H)H]BArF4 ([4-FeH(NH)]BArF4). All of these complexes were characterized by spectroscopic and electrochemical studies; 3-Cl, 3-H and 4-Cl were also characterized by single crystal diffraction studies. 3-H and 4-H are electrocatalysts for H2 (1.0 atm) oxidation in the presence of a excess of the amine base N-methylpyrrolidine, with turnover frequencies at 22 °C of 2.5 s-1 and 0.5 s-1, and overpotentials at Ecat/2 of 235 mV and 95 mV, respectively. Studies of individual chemical and/or electrochemical reactions of the various intermediates provide important insights into the factors governing the overall catalytic activity for H2 oxidation, and provide important insights into the role of the pendant base of the [FeFe] hydrogenase active site. This work was supported by the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

catalysis, iron, hydrogen↗
DOE OSTI2015

Phase-field simulations of GaN growth by selective area epitaxy from complex mask geometries

Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. The model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. The model provides a route to optimize masks and processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

The Role of Pendant Amines in the Breaking and Forming of Molecular Hydrogen Catalyzed by Nickel Complexes

We present the results of a comprehensive theoretical investigation of the role of pendant amine ligands in the oxidation of H2 and formation of H2 by [Ni(P2RN2R’)2]2+ electrocatalysts (where P2RN2R’ is the 1,5-R’-3,7-R derivative of 1,5-diaza-3,7-diphosphacyclooctane with R and R’ are aryl or alkyl groups). We focus our analysis on the thermolchemical part of the catalytic cycle, as it is known to be rate determining for both H2 oxidation and production. We find that the presence of pendant amine functional groups greatly facilitates the heterolytic H2 bond cleavage resulting in a protonated amine functional group and a Ni hydride. Only one single well-positioned pendant amine is required to serve this function. The pendant amine can also effectively shuttle protons to the active site making the redistribution of protons and the H2 evolution a very facile processes. An important requirement for the overall catalytic process is the positioning of at least one amine in close proximity to the metal center. Indeed, only protonation of the pendant amines on the metal center side (endo position) leads to catalytically active intermediates, whereas protonation on the opposite side of the metal center (exo position) leads to a variety of isomers, which are detrimental to catalysis. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under FWP56073.

08 HYDROGEN↗
DOE OSTI2017

Synthesis and Electrocatalytic Activity of [FeFe]‐Hydrogenase Model Complexes with Non‐Innocent Chelating Nitrogen‐Donor Ligands

To probe the influence of redox non‐innocent ligands on a well‐known class of [FeFe]‐hydrogenase models, three new asymmetrically disubstituted diiron complexes of the general formula (µ‐SRS)[Fe(CO) 3 ][Fe(CO)(N‐N)] {SRS = propane‐1,3‐dithiolate (pdt) or benzene‐1,2‐dithiolate (bdt), and N‐N = 2,2′‐bipyridine (bipy) or 2,2′‐bipyrimidine (bpym)} have been synthesized from their parent hexacarbonyls and characterized. The new complexes, (µ‐pdt)Fe 2 (CO) 4 (κ 2 ‐bpym) ( 2 ), (µ‐bdt)Fe 2 (CO) 4 (κ 2 ‐bipy) ( 3 ), and (µ‐bdt)Fe 2 (CO) 4 (κ 2 ‐bpym) ( 4 ), were fully characterized by spectroscopic and electrochemical techniques, and the results are compared to those of a related complex, (µ‐pdt)Fe 2 (CO) 4 (κ 2 ‐bipy) ( 1 ). The crystal structures of 2 – 4 show that, in each complex, the two iron units are in an eclipsed orientation, and the N‐N ligand lies in the basal plane. IR spectra and electrochemical analyses indicate that electron density at the iron centers decreases in the order 1 > 2 > 3 > 4 . Furthermore, compound 2 undergoes a ligand‐centered reduction at the same potential that the hexacarbonyl precursor undergoes its first reduction. However, unlike the 2,2′‐bipy derivatives 1 and 3 , the 2,2′‐bpym complexes 2 and 4 are not effective catalysts for electrochemical proton reduction from acetic acid.

Roy, Souvik↗
DOE OSTI2018

Computational complexity of the landscape II—Cosmological considerations

We propose a new approach for multiverse analysis based on computational complexity, which leads to a new family of “computational” measure factors. By defining a cosmology as a space–time containing a vacuum with specified properties (for example small cosmological constant) together with rules for how time evolution will produce the vacuum, we can associate global time in a multiverse with clock time on a supercomputer which simulates it. We argue for a principle of “limited computational complexity” governing early universe dynamics as simulated by this supercomputer, which translates to a global measure for regulating the infinities of eternal inflation. The rules for time evolution can be thought of as a search algorithm, whose details should be constrained by a stronger principle of “minimal computational complexity”. Unlike previously studied global measures, ours avoids standard equilibrium considerations and the well-known problems of Boltzmann Brains and the youngness paradox. We also give various definitions of the computational complexity of a cosmology, and argue that there are only a few natural complexity classes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Synthesis and Reactivity of Tripodal Complexes Containing Pendant Bases

The synthesis of a new tripodal ligand family is reported, with tertiary-amine groups in the second-coordination sphere. The ligands are tris(amido)amine derivatives, with the pendant amines attached via a peptide coupling strategy. They were designed to be used in new catalysts for the oxygen reduction reaction (ORR), in which the pendant acid/base group could improve catalyst performance. Two members of the new ligand family were each metallated with Co(II) and Zn(II) to afford trigonal monopyramidal complexes. Reaction of the cobalt complexes, [Co(L)]-, with dioxygen reversibly generates a small amount of a Co(III)-superoxo species, which was characterized by EPR. Protonation of the zinc complex Zn[N{CH2CH2NC(O)CH2N(CH2Ph)2}3)-– ([Zn(TNBn)]-) with one equivalent of acid occurs with displacement and dissociation of an amide ligand. Addition of excess acid to the any of the complexes [M(L)]- results in complete proteolysis and formation of the ligands H3L. This decomposition limits the use of these complexes as catalysts for the ORR. An alternative ligand with two pyridyl arms was also prepared but could not be metallated. These studies highlight the importance of stability of the primary-coordination sphere of ORR electrocatalysts to both oxidative and acidic conditions. 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, Office of Science, Office of Basic Energy Sciences.

Blacquiere, Johanna M.↗
DOE OSTI2015

Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Q{sub x} and Q{sub y} transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S{sub 2} of the Spx towards the Q{sub x} state of the B890, and (iii) the internal conversion from Q{sub x} to Q{sub y} within the B890.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of Phosphate on U(VI) Sorption to Montmorillonite: Ternary Complexation and Precipitation Barriers

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated. Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface

Environmental Molecular Sciences Laboratory↗