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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Structural phase transformation and Fe valence evolution in FeOxF2-x/C nanocomposite electrodes during lithiation and de-lithiation processes

In this study, the structural changes of FeOxF2-x/C during the first discharge and recharge cycles were studied by ex situ electron microscopy techniques including annular dark field scanning transmission electron microscopy (DF-STEM) imaging, selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS) as well as by in situ X-ray absorption spectroscopy (XAS). The evolution of the valence state of Fe was determined by combined EELS using the Fe-L edge and XAS using the Fe-K edge. The results of this investigation show that the conversion reaction path during 1st lithiation is very different from the re-conversion path during 1st delithiation. During lithiation, intercalation is first observed followed by conversion into a lithiated rocksalt (Li–Fe–O–F) structure, and metallic Fe and LiF phases. During delithiation, the rocksalt phase does not disappear, but co-exists with an amorphous (rutile type) phase formed initially by the reaction of LiF and Fe. However, a de-intercalation stage is still observed at the end of reconversion similar to a single phase process despite the coexistence of these two (rocksalt and amorphous) phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mesoporous cobalt/manganese oxide: a highly selective bifunctional catalyst for amine–imine transformations

Here, we discuss a heterogeneous catalytic protocol using cobalt doped mesoporous manganese oxide for amine–alcohol cross-coupling to selectively produce symmetric or asymmetric imines. Thorough investigations on the surface chemistry and physical properties of the material revealed its outstanding oxidation–reduction properties and reaction mechanism which was supported by quantum mechanical calculations done by using density functional theory (DFT).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Chicken fat for catalysis: a scaffold is as important for molecular complexes for energy transformations as it is for enzymes in catalytic function

Metalloenzymes are remarkably active, specific, and efficient catalysts.Mimicking the active sites with organometallic complexes based on crystal structures has been a focus for many synthetic chemists. These surrogates have provided significant mechanistic insight into both the molecular complexes as well as the enzymes, however, one of the principle findings has been that just reproducing the active site is not adequate in reproducing the catalytic function. Specifically, the scaffold surrounding the active site plays a critical role in many aspects of catalysis, from positioning reactants optimally to positioning functional groups for reaction to creating the ideal environment for catalysis. Each of these can be controlled with both static positioning as well as small and large dynamics that can activate or control a specific part of the reaction. In this review, we will discuss the effect of organic/peptidic scaffolds, along with medium as an extension of the scaffold, and their varying impacts on catalytic reactivity.

Laureanti, Joseph A.↗
DOE OSTI2015

Epitaxial crystals of Bi{sub 2}Pt{sub 2}O{sub 7} pyrochlore through the transformation of δ–Bi{sub 2}O{sub 3} fluorite

Bi{sub 2}Pt{sub 2}O{sub 7} pyrochlore is thought to be one of the most promising oxide catalysts for application in fuel cell technology. Unfortunately, direct film growth of Bi{sub 2}Pt{sub 2}O{sub 7} has not yet been achieved, owing to the difficulty of oxidizing platinum metal in the precursor material to Pt{sup 4+}. In this work, in order to induce oxidation of the platinum, we annealed pulsed laser deposited films consisting of epitaxial δ–Bi{sub 2}O{sub 3} and co-deposited, comparatively disordered platinum. We present synchrotron x-ray diffraction results that show the nonuniform annealed films contain the first epitaxial crystals of Bi{sub 2}Pt{sub 2}O{sub 7}. We also visualized the pyrochlore structure by scanning transmission electron microscopy, and observed ordered cation vacancies in the epitaxial crystals formed in a bismuth-rich film but not in those formed in a platinum-rich film. The similarity between the δ–Bi{sub 2}O{sub 3} and Bi{sub 2}Pt{sub 2}O{sub 7} structures appears to facilitate the pyrochlore formation. These results provide the only route to date for the formation of epitaxial Bi{sub 2}Pt{sub 2}O{sub 7}.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Pressure-induced phase and chemical transformations of lithium peroxide (Li 2 O 2 )

Here, we present the pressure-induced phase/chemical changes of lithium peroxide (Li 2 O 2 ) to 63 GPa using diamond anvil cells, confocal micro-Raman spectroscopy, and synchrotron x-ray diffraction. The Raman data show the emergence of the major vibrational peaks associated with O 2 above 30 GPa, indicating the subsequent pressure-induced reversible chemical decomposition (disassociation) in dense Li 2 O 2 . The x-ray diffraction data of Li 2 O 2 , on the other hand, show no dramatic structural change but remain well within a P6 3 /mmc structure to 63 GPa. Nevertheless, the Rietveld refinement indicates a subtle change in the structural order parameter z of the oxygen position O (1/3, 2/3, z) at around 35 GPa, which can be considered as a second-order, isostructural phase transition. The nearest oxygen-oxygen distance collapses from 1.56 Å at ambient condition to 1.48 Å at 63 GPa, resulting in a more ionic character of this layered crystal lattice, 3Li + +(LiO 2 )$3-\atop{3}$. This structural change in turn advocates that Li 2 O 2 decomposes to 2Li and O 2 , further augmented by the densification in specific molar volumes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗