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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Synthesis and testing of a composite membrane based on sulfonated polyphenylene oxide and silica compounds as proton exchange membrane for PEM fuel cells

Highlights: • A material based on composite poly (phenylene oxide)/ silica was synthesized and tested as PEM for Hydrogen Fuel Cells. • Sol-gel method has been used to generate silica particles inside the polymer matrix • The presence of silica inside the membrane was highlighted by Energy Dispersive X-ray Fluorescence (EDXRF) spectroscopy. • This membrane has improvements related to: water retention, extension by hydration and tensile strength in hydrated state silica particles inside the polymer matrix • The presence of silica inside the membrane was highlighted by Energy Dispersive X-ray Fluorescence (EDXRF) spectroscopy. • This membrane has improvements related to: water retention, extension by hydration and tensile strength in hydrated state. - Abstract: The present work is an attempt to improve the usseful properties of sulfonated polyphenylene oxide in order to obtain a proton exchange membrane (PEM) for proton exchange membrane fuel cells(PEMFC). Formation of siloxane compounds inside the polymer matrix through an in situ sol-gel process improves properties of the composite membrane: water retention, tensile strength and dimensional stability of the membrane. The presence of the silicone atoms inside the polymer matrix is highlited in the X-ray fluorescence spectra. Parameters related to water absorbtion and proton transport inside the membrane such as: water uptake, hydration number (λ), dimensional expansion by hydration, ion exchange capacity and sulfonation degree show an optimization of the composite membrane compared to the polymeric one. Furthermore, the tensile strength of the composite membranes is better than the polymeric one when both samples are fully hydrated.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural stability of the Li-ion conductor Li7La3Zr2O12 investigated by high-pressure in-situ X-ray diffraction and Raman spectroscopy

Highlights: • Lithium ion conductor of Garnet-related-type structure Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}. • Conversion(M.E.) • High-pressure behavior of Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12} is investigated up to 70 GPa. • High pressure in-situ X-ray diffraction measurements and Raman spectroscopy. • Tetragonal Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12} transforms to high-pressure cubic one under high pressure. - Abstract: The high-pressure behavior of Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12} (LLZO) with a garnet-related structure has been investigated for the first time by high pressure in situ X-ray diffraction measurements and Raman spectroscopy using a diamond anvil cell. It was found that the tetragonal LLZO transforms to the high-pressure cubic phase (HP-c-LLZO) at 71.8 GPa in a N{sub 2} medium and at 25.8 GPa in the absence of pressure mediums. Uniaxial compression in the absence of pressure mediums induced the phase transition at much lower pressures than in the hydrostatic case when N{sub 2} was used as the pressure medium. High pressure in situ Raman spectroscopy suggested that the Li coordination in HP-c-LLZO was different from that reported in cubic LLZO, which had been stabilized by doping Al at ambient pressure and room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2020

DFT Accurate Interatomic Potential for Molten NaCl from Machine Learning

Molten alkali chloride salts are a critical component in concentrated solar power and nuclear applications. Despite their ubiquity, the extreme chemical reactivity of molten alkali chlorides at high temperatures has presented a significant challenge in characterizing atomic structures and dynamic properties experimentally. In this work, we we investigate molten NaCl by performing high temperature molecular dynamics simulations using a Gaussian Approximation Potential (GAP) trained on Density Functional Theory (DFT) datasets. Our GAP model, trained with a meager 1000 atomic configurations, arrives at near ab initio accuracy with a mean absolute error of 1.5 meV/atom thus enabling fast analysis of high temperature salt properties on large length (5000 ion pairs) and time (> 1ns) scales currently inaccessible to ab initio simulations. Calculated structure factors and diffusion constants from our GAP model simulations show excellent agreement with experiments. Our results indicate that GAP models are able to capture the many-body interactions required to accurately model ionic-systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ionic Control over Ferroelectricity in 2D Layered van der Waals Capacitors

The van der Waals layered material CuInP 2 S 6 features interesting functional behavior, including the existence of four uniaxial polarization states, polarization reversal against the electric field through Cu ion migration, a negative-capacitance regime, and reversible extraction of Cu ions. At the heart of these characteristics lies the high mobility of Cu ions, which also determines the spontaneous polarization. Therefore, Cu migration across the lattice results in unusual ferroelectric behavior. Here, we demonstrate how the interplay of polar and ionic properties provides a path to ionically controlled ferroelectric behavior, achieved by applying selected DC voltage pulses and subsequently probing ferroelectric switching during fast triangular voltage sweeps. Using current measurements and theoretical calculations, we observe that increasing DC pulse duration results in higher ionic currents, the buildup of an internal electric field that shifts polarization loops, and an increase in total switchable polarization by ~50% due to the existence of a high polarization phase which is stabilized by the internal electric field. Apart from tuning ferroelectric behavior by selected square pulses, hysteretic polarization switching can even be entirely deactivated and reactivated, resulting in three-state systems where polarization switching is either inhibited or can be performed in two different directions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Broad Applicability of Electrochemical Impedance Spectroscopy to the Measurement of Oxygen Nonstoichiometry in Mixed Ion and Electron Conductors

Oxygen non-stoichiometry is a fundamental feature of mixed ion and electron conductors (MIECs). In this work a general electrochemical method for determining non-stoichiometry in thin film MIECs, via measurement of the chemical capacitance, is demonstrated using ceria and ceria-zirconia (Ce 0.8 Zr 0.2 O 2-δ ) as representative materials. A.C. impedance data are collected from both materials at high temperature (750-900 °C) under reducing conditions with oxygen partial pressure (pO 2 ) in the range 10-13 to 10-20 atm. Additional measurements of ceria-zirconia films are made under relatively oxidizing conditions with pO 2 in the range 0.2 to 10 -4 atm and temperatures of 800-900 °C. Under reducing conditions, the impedance spectra are described by a simple circuit in which a resistor is in series with a resistor and capacitor in parallel, and thickness dependent measurements are used to resolve the capacitance into interfacial and chemical terms. Under more oxidizing conditions, the impedance spectra (of Ce 0.8 Zr 0.2 O 2-δ ) reveal an additional diffusional feature, which enables determination of the ionic resistance of the film in addition to the capacitance, and hence the transport properties. A generalized mathematical formalism is presented for recovering the non-stoichiometry from the chemical capacitance, without recourse to defect chemical models. The ceria non-stoichiometry values are in good agreement with literature values determined by thermogravimetric measurements but display considerably less scatter and are collected on considerably shorter timescales. Here, the thermodynamic analysis of Ce 0.8 Zr 0.2 O 2-δ corroborates earlier findings that introduction of Zr into ceria enhances its reducibility.

08 HYDROGEN↗
DOE OSTI2025

Thermodynamics and transport in molten chloride salts and their mixtures

Relationship between thermophysical properties and phonon mean free path. Heat capacity, viscosity, and thermal conductivity in ionic liquids decrease as mean free path decreases and dynamics become less “solid-like” and collect motion diminishes.

Cockrell, C. [Nuclear Futures Institute, Bangor Un↗
DOE OSTI2020

A Perspective on interfacial engineering of lithium metal anodes and beyond

This Perspective reviews interfacial engineering of lithium metal anodes. Critical issues and open scientific questions related to coatings on the lithium metal anode are discussed. Essential features for ideal coatings, especially those that can potentially enable lithium plating underneath the coating, are highlighted. While most existing approaches use kinetic control to regulate the coating thickness, here we offer a Perspective on thermodynamically controlled interfacial engineering, focusing on spontaneously formed 2D interfacial phases (also known as “complexions”). This approach has been applied to other battery systems but has yet to be realized for lithium metal anodes.

25 ENERGY STORAGE↗
DOE OSTI2022

What is in a name: Defining “high entropy” oxides

High entropy oxides are emerging as an exciting new avenue to design highly tailored functional behaviors that have no traditional counterparts. Study and application of these materials are bringing together scientists and engineers from physics, chemistry, and materials science. The diversity of each of these disciplines comes with perspectives and jargon that may be confusing to those outside of the individual fields, which can result in miscommunication of important aspects of research. In this Perspective, we provide examples of research and characterization taken from these different fields to provide a framework for classifying the differences between compositionally complex oxides, high entropy oxides, and entropy stabilized oxides, which is intended to bring a common language to this emerging area. We highlight the critical importance of understanding a material’s crystallinity, composition, and mixing length scales in determining its true definition.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Competing polar phases in 2D ferroelectric transition metal thio- and selenophosphates

The aim of this Perspective is to provide an in-depth discussion of a certain class of 2D ferroelectrics that feature a van der Waals gap where more than one polar phase can exist energetically close to the ground state. Polar phases of interest can include different ferroelectric, antiferroelectric, and paraelectric phases, which can be transformed into each other through external stimuli, offering unprecedented control over polar material properties. With this level of control, important size limitations and integration problems can be overcome, and material platforms with tunable polar properties for multi-functional devices and sensors can be developed for the next generation of information and energy technologies. We highlight the co-existence of polar properties that have been found on local scales using advanced local characterization techniques as well as methods to control polar properties in transition metal thio-/selenophosphates. In conclusion, we give an overview of future challenges and opportunities in this emerging field of energetically close polar phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Molecular Dynamics Simulation of the Structure and Ion Transport in the Ce{sub 1–x}Gd{sub x}O{sub 2–δ}|YSZ Heterosystem

Molecular dynamics simulation has been used to develop a realistic atomistic model of two-layer Ce{sub 1–x}Gd{sub x}O{sub 2–δ}|YSZ heterosystem. It is shown that Ce{sub 1–x}Gd{sub x}O{sub 2–δ} and YSZ layers (about 15 and 16 Å thick, respectively) retain their crystal structure on the whole. The main structural distortions are found to occur near the Ce{sub 1–x}Gd{sub x}O{sub 2–δ}|YSZ geometric interface, within a narrow interfacial region of few angstroms thick. Both the generalized diffusion characteristics of the system as a whole and the oxygen diffusion coefficients in the layers are calculated, and the diffusion activation energies are determined.

36 MATERIALS SCIENCE↗