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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Hollow Silicon Nanospheres Encapsulated with a Thin Carbon Shell: An Electrochemical Study

In this study we have investigated the electrochemical properties of hollow silicon nanospheres encapsulated with a thin carbon shell, HSi@C, as a potential candidate for lithium-ion battery anodes. Hollow Si nanospheres are formed using a templating method which is followed by carbon coating via carbonization of a pyrrole precursor to form HSi@C. The synthesis conditions and the resulting structure of HSi@C have been studied in detail to obtain the target design of hollow Si nanospheres encapsulated with a carbon shell. The HSi@C obtained exhibits much better electrochemical cycle stability than both micro-and nano-size silicon anodes and deliver a stable specific capacity of 700 mA h g(-1) after 100 cycles at a current density of 2 A g(-1) and 800 mA h g(-1) after 120 cycles at a current density of 1 A g(-1). The superior performance of HSi@C is attributed to the synergistic combination of the nanostructured material, the enhanced conductivity, and the presence of the central void space for Si expansion with little or no change in the volume of the entire HSi@C particle. This study is the first detailed investigation of the synthesis conditions to attain the desired structure of a hollow Si core with a conductive carbon shell. This study also offers guidelines to further enhance the specific capacity of HSi@C anodes in the future. (C) 2016 Elsevier Ltd. All rights reserved.

Anode↗
DOE OSTI2014

Direct Visualization of Solid Electrolyte Interphase Formation in Lithium-Ion Batteries with In Situ Electrochemical Transmission Electron Microscopy

Complex, electrochemically driven transport processes form the basis of electrochemical energy storage devices. The direct imaging of electrochemical processes at high spatial resolution and within their native liquid electrolyte would significantly enhance our understanding of device functionality, but has remained elusive. In this work we use a recently developed liquid cell for in situ electrochemical transmission electron microscopy to obtain insight into the electrolyte decomposition mechanisms and kinetics in lithium-ion (Li-ion) batteries by characterizing the dynamics of solid electrolyte interphase (SEI) formation and evolution. Here we are able to visualize the detailed structure of the SEI that forms locally at the electrode/electrolyte interface during lithium intercalation into natural graphite from an organic Li-ion battery electrolyte. We quantify the SEI growth kinetics and observe the dynamic self-healing nature of the SEI with changes in cell potential.

25 ENERGY STORAGE↗
DOE OSTI2017

Assessment of lead tellurite glass for immobilizing electrochemical salt wastes from used nuclear fuel reprocessing

This paper provides an overview of research evaluating the use of lead tellurite glass as a waste form for salt wastes from electrochemical reprocessing of used nuclear fuel. The efficacy of using lead tellurite glass to immobilize three different salt compositions was evaluated: a LiCl-Li2O oxide reduction salt containing fission products from oxide fuel, a LiCl-KCl eutectic salt containing fission products from metallic fuel, and SrCl2. Physical and chemical properties of glasses made with these salts were characterized with X-ray diffraction, bulk density measurements, differential thermal analysis, chemical durability tests, scanning and transmission electron microscopies, and energy-dispersive X-ray spectroscopy. These glasses were found to accommodate high salt concentrations and have high densities, but further development is needed to improve chemical durability. (C) 2017 Published by Elsevier B.V.

Riley, Brian J.↗
DOE OSTI2017

Size dependent behavior of Fe 3 O 4 crystals during electrochemical (de)lithiation: an in situ X-ray diffraction, ex situ X-ray absorption spectroscopy, transmission electron microscopy and theoretical investigation

Here, the iron oxide magnetite, Fe 3 O 4 , is a promising conversion type lithium ion battery anode material due to its high natural abundance, low cost and high theoretical capacity. While the close packing of ions in the inverse spinel structure of Fe 3 O 4 enables high energy density, it also limits the kinetics of lithium ion diffusion in the material. Nanosizing of Fe 3 O 4 to reduce the diffusion path length is an effective strategy for overcoming this issue and results in improved rate capability. However, the impact of nanosizing on the multiple structural transformations that occur during the electrochemical (de)lithiation reaction in Fe 3 O 4 is poorly understood. In this study, the influence of crystallite size on the lithiation-conversion mechanisms in Fe 3 O 4 is investigated using complementary X-ray techniques along with transmission electron microscopy (TEM) and continuum level simulations on electrodes of two different Fe 3 O 4 crystallite sizes. In situ X-ray diffraction (XRD) measurements were utilized to track the changes to the crystalline phases during (de)lithiation. X-ray absorption spectroscopy (XAS) measurements at multiple points during the (de)lithiation processes provided local electronic and atomic structural information. Tracking the crystalline and nanocrystalline phases during the first (de)lithiation provides experimental evidence that (1) the lithiation mechanism is non-uniform and dependent on crystallite size, where increased Li + diffusion length in larger crystals results in conversion to Fe 0 metal while insertion of Li + into spinel-Fe 3 O 4 is still occurring, and (2) the disorder and size of the Fe metal domains formed when either material is fully lithiated impacts the homogeneity of the FeO phase formed during the subsequent delithiation.

25 ENERGY STORAGE↗
DOE OSTI2020

Dehalogenation of electrochemical processing salt simulants with ammonium phosphates and immobilization of salt cations in an iron phosphate glass waste form

This study demonstrates the conversion of simulated pyroprocessing salt wastes [i.e., ER(SF) and ERV2] into chemically durable iron phosphate glass waste forms through reactions with ammonium hydrogen phosphate precursors [i.e., NH4H2PO4 and (NH4)2HPO4] and added Fe2O3. The reaction of the salt simulants with the phosphate precursors resulted in dehalogenation of the salt through the production of NH4Cl and NH4I (along with water), of which the NH4Cl can be used to produce UCl3 oxidant for use in the electrorefiner during pyroprocessing. These iron phosphate glasses contain a notably higher waste loading than the baseline glass-bonded sodalite ceramic waste form, which requires about 70 vol% sodalite to accommodate Cl from the salt, because they are dehalogenated prior to vitrification. The high waste loadings coupled with higher bulk densities (~3×103 kg/m3) than glass-bonded sodalite (~2.3×103 kg/m3) mean that these glasses have a higher storage volume, i.e., the volume required to immobilize a given mass of waste. The iron phosphate glass waste forms were characterized using a variety of techniques including physical property measurements and chemical durability testing. Following initial testing, a proof-of-concept demonstration was conducted to show that the NH4Cl generated from this process could be used to produce UCl3 using depleted uranium dendrites as a feedstock.

phosphate glass, pyroprocessing, waste forms, salt↗
DOE OSTI2015

Electrochemical Sensors and Biosensors Based on Nanomaterials and Nanostructures

Taking advantages of exceptional attributes, such as easy-to-operate, economical, sensitive, portable, and simple-to- construct, considerable attention has been devoted to the integration of recognition elements with electronic elements to develop electrochemical sensors and biosensors. Recent decades tremendous amounts of attention have been witnessed in this active area. Various electrochemical devices such as amperometric sensors, electrochemical impedance sensors, electrochemical luminescence sensors as well as photoelectrochemical sensors, provide wide applications of detecting chemical and biological targets in terms of electrochemical change of electrode interfaces. With remarkable achievements in nanotechnology and nanoscience, nanomaterial-based electrochemical signal amplifications have great potential of improving both in sensitivity and selectivity for electrochemical sensors and biosensors. First of all, it is well known that the electrode materials play a critical role in the construction of high-performance electrochemical sensing platforms for detecting target molecules through various analytical principles. Furthermore, in addition to electrode materials, functional nanomaterials can not only produce a synergic effect among catalytic activity, conductivity and biocompatibility to accelerate the signal transduction, but also amplify biorecognition events by specifically designed signal tags, leading to highly sensitive biosensing. Sig-nificantly, extensive research on construction of functional electrode materials, coupled with numerous electrochemical methods, is advancing wide applications of electrochemical devices. For example, Walcarius et al. highlighted the recent advances of nano-objects, nano-engineered and/or nanostructured materials for the rational design of bio-functionalized electrodes and related (bio)sensing systems.1 The attractiveness of such nanomaterials relies on their ability to act as effective immobilization matrices, and their intrinsic and unique features as described above. These features combined with the functioning of biomolecules contribute to the improvement of bioelectrode performance in terms of sensitivity and specificity. Our group recently presented a general overview of nanomaterial-enhanced paper-based biosensors including lateral-flow test-strip, and paper microfluidic devices.2With different kinds of nanoparticles (NPs), paper-based biosensor devices have shown great potential in the enhancement of sensitivity and specificity of disease diagnosis in developing countries. This review focuses on recent advances in electrochemical sensors and biosensors based on nanomaterials and nanostructures during 2013 to 2014. The aim of this effort is to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electroanalytical techniques used to the miniaturization and integration of the sensors. Moreover, the authors have attempted to highlight areas of latest and significant development of enhanced elec-trochemical nanosensors and nanobiosensors that inspire broader interests across various disciplines. Electrochemical sensors for small molecules, enzyme-based biosensors, genosensors, immunosensors and cytosensors are reviewed herein (Figure 1). Such novel advances are important for the development of electrochemical sensors as that open up new avenues and methods for future research. Readers interested in the general principles of electrochemical sensors and electrochemical methods are recommended to refer to other excellent literature for a broad scope on this area.3-4 However, due to the explosion of publications in this active field, we do not claim that this review includes all of the published works in the past two years. Due to the large activity in this field we apologize to the authors of excellent work, which is unintentionally left out.

Zhu, Chengzhou↗
DOE OSTI2017

Synthesis and electrochemical characterization of Ti{sub x}Ta{sub y}Al{sub z}N{sub 1-δ}O{sub γ} for fuel cell catalyst supports

Quinary Ti{sub x}Ta{sub y}Al{sub z}N{sub 1-δ}O{sub γ} of various compositions have been prepared by a co-precipitation method followed by ammonolysis. The nitride samples were examined as potential catalyst supports in polymer electrolyte membrane fuel cells. The nitride products crystallized in the rock salt (NaCl) structure over a wide range of compositions. The addition of Ta and Al was highly beneficial towards improving the chemical and electrochemical stability of TiN, without a significant loss of electrical conductivity. Platinum particles were successfully deposited on the (oxy)nitride samples, and the composite samples at some compositions were found to be comparable to Pt/carbon in their stability and catalytic activity even without optimizing the Pt deposition and dispersion processes. - Graphical abstract: The effect of additions of Ta and Al into TiN structure. Shifts the lattice constant, and increases its chemical stability in acidic environment.

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

Direct Comparison of Electrochemical and Spectrochemical Kinetics for Catalytic Oxygen Reduction

We describe here a direct comparison of electrochemical and spectrochemical experiments to determine rates and selectivity of oxygen reduction catalyzed by iron 5,10,15,20-meso-tetraphenylporphyrin chloride. Strong agreement was found between the two methods suggesting the same mechanism is occurring under both conditions, with the same overall third order rate constant kcat = (1.1 ± 0.1) × 106 M-2 s-1. This report provides a rare example of characterization of a redox catalytic process by two common but very different methods. This work 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, Basic Energy Sciences.

Wasylenko, Derek J.↗
DOE OSTI2017

Electrochemical (de)lithiation of silver ferrite and composites: mechanistic insights from ex situ, in situ, and operando X-ray techniques

Here, the structure of pristine AgFeO 2 and phase makeup of Ag 0.2 FeO1.6 (a one-pot composite comprised of nanocrystalline stoichiometric AgFeO 2 and amorphous γ-Fe 2 O 3 phases) was investigated using synchrotron x-ray diffraction. A new stacking-fault model was proposed for AgFeO2 powder synthesized using the co-precipitation method. The lithiation/de-lithiation mechanisms of silver ferrite, AgFeO 2 and Ag 0.2 FeO 1.6 were investigated using ex-situ, in-situ, and operando characterization techniques. An amorphous γ-Fe 2 O 3 component in the Ag 0.2 FeO 1.6 sample is quantified. Operando XRD of electrochemically reduced AgFeO 2 and Ag 0.2 FeO 1.6 composites demonstrated differences in the structural evolution of the nanocrystalline AgFeO 2 component. As complimentary techniques to XRD, ex-situ x-ray Absorption Spectroscopy (XAS) provided insight into the short-range structure of the (de)lithiated nanocrystalline electrodes, and a novel in-situ high energy x-ray fluorescence nanoprobe (HXN) mapping measurement was applied to spatially resolve the progression of discharge. Based on the results, a redox mechanism is proposed where the full reduction of Ag + to Ag0 and partial reduction of Fe 3+ to Fe 2+ occur on reduction to 1.0 V, resulting in a Li 1+y Fe III Fe II yO 2 phase. The Li 1+y Fe III Fe II yO 2 phase can then reversibly cycle between Fe 3+ and Fe 2+ oxidation states, permitting good capacity retention over 50 cycles. In the Ag 0.2 FeO 1.6 composite, a substantial amorphous γ-Fe 2 O 3 component is observed which discharges to rock salt LiFe 2 O 3 and Fe 0 metal phase in the 3.5 – 1.0 V voltage range (in parallel with the AgFeO 2 mechanism), and reversibly reoxidizes to a nanocrystalline iron oxide phase.

25 ENERGY STORAGE↗