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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Synthesis of porous MnO2-CoO microsheets and nanocones as a high-performance battery-type capacitive material

Highlights: • Porous MnO{sub 2}-CoO microsheets and nanocones (MCMSNCs) are synthesized. • Sodium dodecyl sulfate controls the formation of specific metal oxide structures. • MCMSNCs deliver excellent capacitive performance as a battery-type material. - Abstract: A facile method via sodium dodecyl sulfate (SDS)-templated oil-bath followed by annealing treatment is reported to synthesize porous MnO{sub 2}-CoO microsheets and nanocones (MCMSNCs). Herein, surfactant SDS is firstly used to obtain Mn/Co hydroxide ultrathin microsheets and nanocones precursor, which is then transformed into interconnected porous MCMSNCs after heat treatment. As a battery-type capacitive electrode micro/nanomaterial, MCMSNCs exhibit an original specific capacity (148 C g{sup −1}) at a current density of 1 A g{sup −1} by chronopotentiometry. Moreover, MCMSNCs deliver good rate performance with 77% capacity retention from 1 to 16 A g{sup −1} and excellent cycle life with 20% loss of the maximum value as well as 118% retention of the initial one after 3000 cycles. The excellent capacitive performance of porous MCMSNCs endows it potential use as an anode electrode material in the application of electrochemical capacitors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

High energy storage density of temperature-stable X9R ceramics

Highlights: • The addition of KNbO{sub 3} improved the temperature-stable properties and energy density. • The x = 0.07 and x = 0.09 sample met the X8R requirements. • The x = 0.03 and x = 0.05 sample met the X9R requirements. • The maximum discharge energy density of x = 0.05 sample reached up to 2 J/cm{sup 3} at 17.85 kV/mm. - Abstract: The effects of KNbO{sub 3} addition on the temperature stability of dielectric properties and energy-storage performances of Sr{sub 0.5}Na{sub 0.25}Bi{sub 0.25}TiO{sub 3}-MgO ((1-x)SNBTM5-xKN) ceramics were systematically investigated. It shows that KNbO{sub 3} has completely diffused into SNBT lattice to form a solid solutions. Two obvious maxima in permittivity curves were observed due to the formation of the polar nanoregions. For the sample with x = 0.05 addition, its permittivity variation region, where △ε'/ε'{sub 25 °C} is no more than ± 15%, retains wide the range from −55 °C to 200 °C, indicating that the ceramics can meet the requirement of X9R specification. Furthermore, this sample shows a high electric breakdown strength of 17.85 kV/mm and a high discharge energy density of 2 J/cm{sup 3}. The noticeable reduced remnant polarization induced by KNbO{sub 3} addition also contributes to the improved energy-storage performances. Thus, these novel ceramics with the aforementioned characteristics will potentially benefit the applications of high pulse power capacitors at high temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A bi-functional ferroelectric Pb(Zr0.52Ti0.48)O3 films: Energy storage properties and ferroelectric photovoltaic effects

Highlights: • PZT films by sol-gel method exhibited a higher energy densities (∼11.2 J/cm{sup 3}) and energy conversion efficiency (∼68%). • Pt/PZT/Pt devices showed the higher open circuit voltage (V{sub oc} ∼1 V), larger short circuit current (J{sub sc} ∼0.1 mA/cm{sup 2}). • Pt/PZT/Pt devices might improve the properties of energy storage and photovoltage in ferroelectric films. - Abstract: In this work, we reported a bi-functional ferroelectric Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3} (PZT) films which show energy storage properties and photovoltaic effects. The PZT films were crystallized into pure pseudo-cubic structure with the (001) preferred orientation. The polarization characterizations revealed a large recoverable energy storage density (∼11.2 J/cm{sup 3}) and a high energy conversion efficiency (∼68%) with good thermal stability (25 °C–100 °C) and fast response (>10 Hz). Meanwhile, the Pt/PZT/Pt capacitor presented a significant photovoltaic effect. The open circuit voltage and the short circuit current were -0.92 V and 139 μA/cm{sup 2} at original state, respectively, while they were slightly increased to -1.01 V and 155 μA/cm{sup 2} in polarization-up state, and slightly decreased to -0.77 V and 90 μA/cm{sup 2} in polarization-down state. The maximum power conversion efficiency was enhanced one order of magnitude than that of polycrystalline PZT film reported elsewhere. Our study opens up a pathway toward developing bi-functional ferroelectric devices with simultaneously high energy storage density and high photovoltaic performance.

14 SOLAR ENERGY↗
DOE OSTI2017

Electric double layer capacitance for ionic liquids in nanoporous electrodes: Effects of pore size and ion composition

The energy density of an electric double layer (EDL) capacitor, a type of supercapacitor, depends on the ion distribution within the micropores of electrodes that are typically made of amorphous carbon. By using coarse-grained models and the classical density functional theory, we investigate the distributions of ionic species among different idealized nanopores in contact with an asymmetric ionic liquid mixture and the effects of the bulk electrolyte composition on capacitive energy storage. We find that a charged pore is always small-ion selective, provided all ions have the same valence and similar non-electrostatic interactions. While small ions enhance both the EDL capacitance and the accessibility of micropores, an ionic mixture containing ions of different sizes may yield a capacitance higher than those corresponding to pure ionic liquids. Furthermore, the increased capacitance may be attributed to more efficient ion packing near the charged surface. At certain conditions, the improvement is on a par with the anomalous capacitance rise for pure ionic liquids in electrodes with ultranarrow pores.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Solid-state polymer magnesium supercapacitor

Here, the present article focuses on the development of a highly ion-conductive, solvent-free, solid-state polymer electrolyte membrane (PEM) via photopolymerization of polyethylene glycol diacrylate (PEGDA) network from its homogeneous melt mixtures containing succinonitrile (SCN) plasticizer and magnesium bis(trifluoromethane sulfonyl) imide Mg(TFSI) 2 salt. The above solid-state Mg-PEM exhibits a Helmholtz electric double-layer capacitor (EDLC) behavior in its supercapacitive symmetric carbonaceous electrode configuration. The electrochemical stability for this PEM membrane (20/40/40 PEGDA/SCN/Mg (TFSI) 2 ) was found to be approximately 3 V from linear sweep voltammetry with a specific capacitance of about 44 F/g from cyclic voltammetry and an energy density of approximately 17 Wh/kg in the 0–2 V range from the constant current density (CCD) experiment. Of particular interest is its excellent capacity retention of over 11,200 cycles, thus tested with the Coulombic efficiency of over 87%. Moreover, the energy density after extensive cycling for 11,200 has increased to approximately 56 Wh/kg at 10 mV/s in the potential range of 0–3 V relative to 17 Wh/kg in the potential range of 0–2 V at the same scan rate, attesting the excellent electrochemical stability and long life of the present Mg-PEM supercapacitor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Ion-Exchange and Cation Solvation Reactions in Ti 3 C 2 MXene

Ti 3 C 2 and other two-dimensional transition metal carbides known as MXenes are currently being explored for many applications involving intercalated ions, from electrochemical energy storage, to contaminant sorption from water, to selected ion sieving. We report here a systematic investigation of ion exchange in Ti 3 C 2 MXene and its hydration/dehydration behavior. We have investigated the effects of the presence of LiCl during the chemical etching of the MAX phase Ti 3 AlC 2 into MXene Ti 3 C 2 T x (T stands for surface termination) and found that the resulting MXene has Li + cations in the interlayer space. We successfully exchanged the Li + cations with K + , Na + , Rb + , Mg 2+ , and Ca 2+ (supported by X-ray photoelectron and energy-dispersive spectroscopy) and found that the exchanged material expands on the unit-cell level in response to changes in humidity, with the nature of expansion dependent on the intercalated cation, similar to behavior of clay minerals; stepwise expansions of the basal spacing were observed, with changes consistent with the size of the H 2 O molecule. Thermogravimetric analysis of the dehydration behavior of these materials shows that the amounts of H 2 O contained at ambient humidity correlates simply with the hydration enthalpy of the intercalated cation, and that the diffusion of the exiting H 2 O proceeds with kinetics similar to clays. Furthermore, these results have implications for understanding, controlling, and exploiting structural changes and H 2 O sorption in MXene films and powders utilized in applications involving ions, such as electrochemical capacitors, sensors, reverse osmosis membranes, or contaminant sorbents.

36 MATERIALS SCIENCE↗
DOE OSTI2022

NMR and Theoretical Study of In-Pore Diffusivity of Ionic Liquid–Solvent Mixtures

We report despite having a lower energy density than common batteries, electric double-layer capacitors (EDLCs) offer several advantages for high-power applications, including high power density, quick charge and discharge time, and long cycle life. Room-temperature ionic liquids (RTILs) have been intensely studied as promising electrolytes for applications in ELDCs because of their wide potential window, low volatility, as well as thermal and chemical stability. The main deficiency of neat RTILs in such applications is the sluggish diffusivity, which restricts the EDLCs’ power density. To alleviate the slow diffusivity, RTILs can be used in a mixture with organic solvents. In this study, we applied two-dimensional exchange nuclear magnetic resonance spectroscopy (2D EXSY NMR) and molecular dynamics (MD) simulations to investigate the diffusivity of anions of an RTIL, namely, 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (BMIM + –TFSI – ), dissolved in five different organic solvents, in the micropores of activated carbon. We determined that the relative concentrations of ions in solutions in the micropores were higher than those in the bulk solutions and were also solvent-dependent. The ion diffusivities in the pores were found to be almost 2 orders of magnitude slower than in the bulk solutions, with methanol showing the largest relative disparity. These results suggested that the interactions of solvents with the activated carbon are critical not only to the power density of EDLCs but also to the energy density. The comparisons of ion diffusivities between the experiments and the MD simulations suggest the need to consider also the surface functionalities of activated carbon for the simulation of ion diffusion in the micropores of activated carbon.

electric double layer capacitors↗
DOE OSTI2016

A Generic Model for Electric Double Layers in Porous Electrodes

The performance of electric-double-layer capacitors (EDLCs) hinges on microscopic charge distributions near the electrode/electrolyte interfaces. Whereas practical EDLCs consist of electrodes made of amorphous porous materials, theoretical understanding of EDLCs is mostly based on EDL structure near a planar surface or on simplistic models that have little relevance to realistic systems. In this work, we propose a spherical shell model to account for both pore size and curvature effects of amorphous porous materials. The EDL structure in spherical shells has been investigated over a broad range of pore sizes and curvatures by use of classic density functional theory. Theoretical results reveal that the curvature effects on convex and concave EDLs are drastically different and that materials with extensive convex surfaces will lead to maximized capacitance. Like a slit pore, the spherical shell model also predicts oscillatory variation of capacitance with pore size, but the oscillatory behavior is magnified as the curvature increases. The joint effects of pore size and curvature identified in this work give new insight into materials design for porous electrodes with optimal EDLC performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Electrochemical Behavior of Nanoporous Supercapacitors with Oligomeric Ionic Liquids

According to a recent study [Matsumoto, M. ; J. Am. Chem. Soc. 2017, 139, 16072-16075], an oligomeric ionic liquid (OIL) may exhibit a wide electrochemical window and an exceptionally high capacitance in electric double layer (EDL) transistors. However, little is known on applicability of OILs in EDL capacitors with porous electrodes. To understand the capacitive performance of OILs, here we investigate the charging behavior, EDL structure, and capacitance for different types of OILs using the classical density functional theory. In contrast to their application to field-effect transistors, the capacitive performance of OILs in nanoporous electrodes is sensitive to the charging potential. We report that although adoption of oligomeric cations shows little advantage for the electrical charging of a positive electrode, they enhance the energy storage density for negative electrodes.

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

Toward Polarization-Switched Molecular Pumps

Pumping of fluids is universally performed by using mechanical or thermal compressors. We demonstrate for the first time a new solid-state molecular pumping mechanism induced by switching the adsorption affinity for a gas through polarization of a chromophore under an applied electric field. Mass spectrometry was used to trace refrigerant gas (difluoromethane) uptake on a chromophore-coated capacitor under applied voltage and subsequent desorption when the voltage and electrode polarization was removed showing an exchange capacity of 0.11 mol of refrigerant per liter of chromophore. Calorimetry confirmed a reversible enthalpy change of 9 Kcal/mol in the polarization-induced sorption-desorption process. Here, the present work establishes the principle and feasibility of non-mechanical molecular pumping, which can be exploited for refrigeration, catalysis, gas separation, among many other potential applications.

42 ENGINEERING↗
DOE OSTI2020

Revealing Antiferroelectric Switching and Ferroelectric Wakeup in Hafnia by Advanced Piezoresponse Force Microscopy

Hafnium oxide (HfO 2 )-based ferroelectrics offer remarkable promise for memory and logic devices in view of their compatibility with traditional silicon complementary metal oxide semiconductor (CMOS) technology, high switchable polarization, good endurance, and thickness scalability. These factors have led to a steep rise in the level of research on HfO 2 over the past number of years. While measurements on capacitors are promising for understanding macroscopic effects, many open questions regarding the emergence of ferroelectricity and electric field cycling behaviors remain. Continued progress requires information regarding the nanoscale ferroelectric behaviors on the bare surface (i.e., without encapsulation), which is notably absent. To overcome this barrier, we have applied complementary modes of piezoresponse force microscopy with the goal of directly and quantitatively sensing nanoscale ferroelectric behaviors in bare HfO 2 thin films. Our results on 8 nm Si-doped HfO 2 reveal nanoscale domains of local remnant polarization states exhibiting a weak piezoelectric coupling (deff) in the range 0.6–1.5 pm/V. While we observed localized enhancement of deff during progressive stressing of the bare HfO 2 thin film, we did not detect stable polarization switching which is a prerequisite of ferroelectric switching. We find that this result could be explained using polarization switching spectroscopy which revealed antiferroelectric-like switching in the form of pinched hysteresis loops as well as increasing remnant response with repeated cycling. As such, our results offer a promising route for material scientists who want to explore the nanoscale origins of antiferroelectricity and ferroelectric wakeup in HfO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Study of X-pinch dynamics using a low current (25 kA) and slower current (400 ns) pulse

We report on experiments examining the dynamics of low current (25 kA), long rise-time (400 ns) X-pinches. The experiments used two- and four-wire 5 {mu}m tungsten X-pinches. We discuss coronal plasma dynamics, X-ray emission, cross-point evolution, and axial column dynamics. We show that the pinch dynamics are akin to those in X-pinches driven by 0.1-1 MA and at rise-rates from 0.25 to 10 kA/ns. We observe soft X-rays ({approx}1-2 keV range) emitted from the cross point in both two-wire and four-wire X-pinches at about peak current. These results show that compact current generators consisting of 2-4 small capacitors in a simple capacitive discharge circuit can produce good quality pinches for applications in Thomson X-ray scattering and backlighting among others.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Low temperature dielectric relaxation and charged defects in ferroelectric thin films

We report a dielectric relaxation in BaTiO{sub 3}-based ferroelectric thin films of different composition and with several growth modes: sputtering (with and without magnetron) and sol-gel. The relaxation was observed at cryogenic temperatures (T < 100 K) for frequencies from 100 Hz up to 10 MHz. This relaxation activation energy is always lower than 200 meV and is very similar to the relaxation that we reported in the parent bulk perovskites. Based on our Electron Paramagnetic Resonance (EPR) investigation, we ascribe this dielectric relaxation to the hopping of electrons among Ti{sup 3+}-V(O) charged defects. Being dependent on the growth process and on the amount of oxygen vacancies, this relaxation can be a useful probe of defects in actual integrated capacitors with no need for specific shaping.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Negative compressibility observed in graphene containing resonant impurities

We observed negative compressibility in monolayer graphene containing resonant impurities under different magnetic fields. Hydrogenous impurities were introduced into graphene by electron beam (e-beam) irradiation. Resonant states located in the energy region of {+-}0.04 eV around the charge neutrality point were probed in e-beam-irradiated graphene capacitors. Theoretical results based on tight-binding and Lifshitz models agreed well with experimental observations of graphene containing a low concentration of resonant impurities. The interaction between resonant states and Landau levels was detected by varying the applied magnetic field. The interaction mechanisms and enhancement of the negative compressibility in disordered graphene are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

High-bandwidth polarimeter for a high density, accelerated spheromak

A three-beam heterodyne polarimeter has been built to diagnose the PI-1 plasma injector at General Fusion, Inc. The polarimeter measures plasma density and Faraday rotation, which can provide estimates of magnetic field magnitude and direction. Two important calibration steps are required for the polarimeter to produce reasonable Faraday rotation signals. Beam polarization ellipticity must be measured to ensure there is a linear Faraday rotation response. In addition, the two beams travelling through the plasma must be collinear to reduce error due to differences in plasma density. Once calibrated, the Faraday rotation signals are in much better agreement with other diagnostics. For a null signal, the Faraday rotation measurement noise floor is 0.1° at 0.5 MHz bandwidth. Comparing preliminary spheromak Faraday rotation measurements to a model, the maximum error is about 0.3° at 0.5 MHz bandwidth, which is primarily due to electrical noise during the injector's capacitor discharge and limitations of the model. At a bandwidth of 0.5 MHz, the polarimeter has an axial resolution between 6 cm and 30 cm depending on the speed of the spheromak, which varies between 30 km/s and 150 km/s. The spheromak length ranges from 0.75 m to 2 m. Additional polarimeter chords will be added in future upgrades.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Optimization of the parameters of plasma liners with zero-dimensional models

The efficiency of conversion of the energy stored in the capacitor bank of a high-current pulse generator into the kinetic energy of an imploding plasma liner is analyzed. The analysis is performed by using a model consisting of LC circuit equations and equations of motion of a cylindrical shell. It is shown that efficient energy conversion can be attained only with a low-inductance generator. The mode of an 'ideal' load is considered where the load current at the final stage of implosion is close to zero. The advantages of this mode are, first, high efficiency of energy conversion (80%) and, second, improved stability of the shell implosion. In addition, for inertial confinement fusion realized by the scheme of a Z pinch dynamic hohlraum, not one but several fusion targets can be placed in the cavity on the pinch axis due to the large length of the liner.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Role of polaron hopping in leakage current behavior of a SrTiO{sub 3} single crystal

We studied the ionic/electronic transport and resistance degradation behavior of dielectric oxides by solving the electrochemical transport equations. Here, we took into account the non-periodical boundary conditions for the transport equations using the Chebyshev collocation algorithm. A sandwiched Ni|SrTiO{sub 3}|Ni capacitor is considered as an example under the condition of 1.0 V, 1.0 μm thickness for SrTiO{sub 3} layer, and a temperature of 150 °C. The applied voltage resulted in the migration of ionic defects (oxygen vacancies) from anode towards cathode. The simulated electric potential profile at steady state is in good agreement with the recent experimental observation. We introduced the possibility of polaron-hopping between Ti{sup 3+} and Ti{sup 4+} at the electrode interface. It is shown that both the oxygen vacancy transport and the polaron-hopping contribute to the resistance degradation of single crystal SrTiO{sub 3}, which is consistent with the experimental observations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

A concept for a magnetic field detector underpinned by the nonlinear dynamics of coupled multiferroic devices

Multiferroic (MF) composites, in which magnetic and ferroelectric orders coexist, represent a very attractive class of materials with promising applications in areas, such as spintronics, memories, and sensors. One of the most important multiferroics is the perovskite phase of bismuth ferrite, which exhibits weak magnetoelectric properties at room temperature; its properties can be enhanced by doping with other elements such as dysprosium. A recent paper has demonstrated that a thin film of Bi{sub 0.7}Dy{sub 0.3}FeO{sub 3} shows good magnetoelectric coupling. In separate work it has been shown that a carefully crafted ring connection of N (N odd and N ≥ 3) ferroelectric capacitors yields, past a critical point, nonlinear oscillations that can be exploited for electric (E) field sensing. These two results represent the starting point of our work. In this paper the (electrical) hysteresis, experimentally measured in the MF material Bi{sub 0.7}Dy{sub 0.3}FeO{sub 3}, is characterized with the applied magnetic field (B) taken as a control parameter. This yields a “blueprint” for a magnetic (B) field sensor: a ring-oscillator coupling of N = 3 Sawyer-Tower circuits each underpinned by a mutliferroic element. In this configuration, the changes induced in the ferroelectric behavior by the external or “target” B-field are quantified, thus providing a pathway for very low power and high sensitivity B-field sensing.

36 MATERIALS SCIENCE↗