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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Exploring the potential of high entropy perovskite oxides as catalysts for water oxidation

Electrochemical water splitting is a promising technology to renewably generate hydrogen from water with no carbon footprint. However, the catalytic efficiency is hindered by the sluggishness of the oxygen evolution reaction (OER) at the anode. Therefore, developing earth-abundant, stable, and efficient OER catalysts is of keen interest. Recent studies have demonstrated that high entropy perovskite oxides (HEPOs) can exhibit superior OER activity and excellent electrochemical stability due to the synergistic effects of the multiple cations and the high entropy configuration effect. In this opinion paper, we point out the strengths and discuss the challenges and future prospects for HEPO-based electrocatalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Unravelling high-temperature stability of lithium-ion battery with lithium-rich oxide cathode in localized high-concentration electrolyte

Lithium (Li)-rich manganese (Mn)-rich oxide (LMR) cathode materials, despite of the high specific capacity up to 250 mAh g-1 suffer from instability of cathode/electrolyte interfacial layer at high working voltages, causing continuous voltage decay and capacity fading, especially at elevated temperatures. In various battery systems, localized high-concentration electrolytes (LHCEs) have been widely reported as a promising candidate to form effective electrode/electrolyte interphases. Here, an optimized LHCE is studied in graphite (Gr)-based full cells being cycled at 25, 45 and 60 °C with the reference of a conventional LiPF6-based electrolyte. It is revealed that the LHCE can effectively suppress continuous electrolyte decompositions and mitigate the dissolution of Mn ions due to the formation of more protective electrode/electrolyte interphases on both anode and cathode, which, in turn, lead to significantly improved cycling stability and enhanced rate capability under the selected temperatures. The mechanistic understanding on the failure of the conventional LiPF6-containing electrolyte and the function of the LHCE in Gr||LMR cells under high temperatures provides valuable perspectives of electrolyte development for practical application of LMR cathodes in high energy density batteries over a wide temperature range.

Localized high-concentration electrolyte, Lithium-↗
DOE OSTI2023

Investigating the effect of aluminum oxide fixed charge on Schottky barrier height in molybdenum oxide-based selective contacts

A tunneling atomic layer deposited (ALD) AlO x layer was inserted in a Si|SiO x |AlO x |MoO x |metal tunnel diode structure to investigate the impact of fixed interface charge on Schottky barrier height. ALD AlO x provides a synthesis-tunable fixed charge and can provide excellent field effect passivation at the SiO x |AlO x interface. A large (>1 × 10 12 q.cm –2 ) negative fixed charge density was expected to decrease Schottky barrier height on p-type silicon and increase Schottky barrier height on n-type silicon by up to 0.4 eV based on an electrostatic model. Fixed charge density and interface trap state density were measured using a thick layer of AlO x in metal oxide semiconductor capacitor structures (MOSCAPs); Schottky barrier height and specific contact resistivity were measured using a tunneling-active layer of AlO x in contacted structures with MoO x . In some samples, HfO x interface layers were inserted between AlO x and silicon to quench the fixed negative charge. The Schottky barrier height was found to vary with processing conditions but did not have a strong correlation with expected fixed charge density. Here, while fixed charge may play a role in determining the Schottky barrier height, other parameters also have significant affect. Further work is needed to minimize contact resistivity and elucidate other factors impacting the Schottky barrier height.

14 SOLAR ENERGY↗
DOE OSTI2018

Comprehensive Magnetic Study of Nanostructured Mesoporous Manganese Oxide Materials and Implications for Catalytic Behavior

Magnetic behavior of nanostructured mesoporous manganese oxide materials, designated UCT-1 and UCT-18, were studied using a combination of superconducting quantum interference device (SQUID) magnetometry and 55 Mn zero-field spin–echo nuclear magnetic resonance (NMR). Curie–Weiss fits to the magnetic susceptibility for the UCT-1 and UCT-18 samples calcined at 550 °C yielded paramagnetic moment values consistent with spin-only Mn 3+ ions in the α-Mn 2 O 3 phase ( S = 2, 4.90 μ B ). However, the magnetization and NMR results reported here clearly identify a small amount of the Mn 3 O 4 second phase (ferrimagnetic with T C ≈ 43 K) that does not appear in X-ray diffraction (XRD). We report the study resulted in the observation of fascinating magnetic behavior: (1) exchange bias, which occurs in cases where a ferromagnetic (or ferrimagnetic) phase forms a boundary with an antiferromagnetic phase and (2) a magnetic contribution attributed to uncompensated spins on the surfaces of the α-Mn 2 O 3 nanoparticles. The presence of Mn 3 O 4 and the interplay of Mn 3+ and Mn 2+ impact the catalytic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Large enhancement in the heterogeneous oxidation rate of organic aerosols by hydroxyl radicals in the presence of nitric oxide

In this paper we report an unexpectedly large acceleration in the effective heterogeneous OH reaction rate in the presence of NO. This 10–50 fold acceleration originates from free radical chain reactions, propagated by alkoxy radicals that form inside the aerosol by the reaction of NO with peroxy radicals, which do not appear to produce chain terminating products (e.g., alkyl nitrates), unlike gas phase mechanisms. Lastly, a kinetic model, constrained by experiments, suggests that in polluted regions heterogeneous oxidation plays a much more prominent role in the daily chemical evolution of organic aerosol than previously believed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Gigahertz acoustic vibrations of elastically anisotropic Indium–tin-oxide nanorod arrays [Gigahertz modulation of the full visible spectrum via acoustic vibrations of elastically anisotropic Indium-tin-oxide nanorod arrays]

Active control of light is important for photonic integrated circuits, optical switches,. and telecommunications. Coupling light with acoustic vibrations in nanoscale optical resonators offers optical modulation capabilities with high bandwidth and Small footprint Instead of using noble metals, here we introduce indium tin-oxide nanorod arrays (ITO-NRAs) as the operating media;and demonstrate optical modulation covering the visible spectral range (from 360 to 700 nm), with similar to 20 GHz bandwidth through the excitation of coherent acoustic vibrations in ITO-NRAs. This broadband modulation results from the collective optical diffraction by the dielectric ITO-NRAs, and a high differential transmission modulation up to 10% is achieved through efficient near-infrared, on-plasmon-resonance pumping. By combining the frequency signatures Of the vibrational modes with finite-element simulations, we,further determine the anisotropic elastic constants for single-crystalline ITO, which are not known-for the bulk phase. Furthermore, this technique to determine elastic constants using Coherent acoustic vibrations of uniform nanostructures can be generalized to the study of other inorganic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Metastable Intermediates in Amorphous Titanium Oxide: A Hidden Role Leading to Ultra-Stable Photoanode Protection

Metastable intermediates represent a non-equilibrium state of matter that may impose profound impacts to materials properties beyond our understandings of monolithic and equilibrium systems. Here, we report a discovery of hidden metastable intermediates in amorphous TiO 2 thin films and their critical role in electrochemical damage. These intermediates have a non-bulk crystal-like structure and exhibit significantly higher electrical conductivity than both the amorphous and the crystalline phases. When these TiO 2 films are applied to protect Si photoelectrochemical (PEC) photoanodes, the intermediates can induce localized high electrical currents that largely accelerate the etching of the TiO 2 film and the Si electrode underneath. The intermediates can be effectively suppressed by raising their nucleation barrier via reducing the film thickness from 24 to 2.5 nm. The homogeneous amorphous TiO 2 -film-coated Si photoanodes achieved more than 500 h of PEC water oxidation at a steady photocurrent density of over 30 mA·cm –2 .

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Influence of Reactor Parameters on the Boron Nitride-Catalyzed Oxidative Dehydrogenation of Propane

In this contribution, we investigate the effect of various reactor parameters on the oxidative dehydrogenation (ODH) of propane using a hexagonal boron nitride (hBN) heterogeneous catalyst. Here, the analysis begins with an assessment of the influence of mass and heat transport on the observed ODH activity. Unexpected experimental results during this analysis prompted us to investigate the use of SiC as an inert catalyst diluent, and we found an increase in propane conversion with increasing diluent content in the reactor. Control experiments suggested that SiC itself is catalytically inactive and that there may be a significant influence of gas-phase chemistry on the observed reactivity.

03 NATURAL GAS↗
DOE OSTI2018

Low-Temperature Methane Partial Oxidation to Syngas with Modular Nanocrystal Catalysts [Targeting Low-Temperature Methane Partial Oxidation to Syngas with Modular Nanocrystal Catalysts]

Here, the low-temperature conversion of methane into value-added products is an appealing goal due to the abundance of methane in the form of natural gas. Industrially, methane is used to produce synthesis gas (syngas), a precursor mixture used heavily in the production of ammonia, methanol, and synthetic fuels. In practice, this mixture is produced via the energy-intensive methane steam reforming reaction at temperatures between 750 and 1450 °C. The exothermic methane partial oxidation reaction stands as an alternative for syngas formation at lower temperatures, especially for gas to liquid fuels applications, yet awaits large-scale implementation due to dangerous operating conditions and temperatures. Using colloidally synthesized Ru catalysts, we identify two unifying rules that govern the low-temperature production of synthesis gas: depletion of oxygen within the catalyst bed and facile RuO 2 → Ru reduction kinetics, which is a strong function of supporting material and Ru nanostructure. Using these design rules, we demonstrate the enhanced low-temperature activity of a bifunctional Ru/Pd catalyst which produces synthesis gas at ~400 °C, with nearly complete CH 4 conversion and CO selectivity at 670 °C.

03 NATURAL GAS↗
DOE OSTI2023

Selective Electrocatalytic Reduction of Nitrous Oxide to Dinitrogen with an Iron Porphyrin Complex

Nitrous oxide (N 2 O) is the third largest contributor to anthropogenic greenhouse gas emissions and plays a detrimental role in the depletion of ozone. Despite the contribution of N 2 O as an atmospheric pollutant, there are currently only a few examples of electrochemical N 2 O remediation to N 2 . Herein we report the electrocatalytic deoxygenation of N 2 O by iron tetraphenylporphyrin (FeTPP) to form N 2 with quantitative Faradaic efficiency and an observed rate of 1.91 s –1 . No degradation was observed after controlled potential electrolysis. Mechanistic investigation of the proposed catalytic steps determined that hydrogen-bond donors are critical for accelerating N 2 O activation and that proton transfer is involved in the rate-determining step.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Effect of Electrolyte Ions on Iridium Oxide-Based Water Oxidation Catalysis

The oxygen evolution reaction often limits the efficiency of renewable fuel syntheses due to its sluggish reaction kinetics. Of the factors that have been studied to improve this important reaction is how the choice of the electrolyte may alter the reaction kinetics. Despite its importance, sys-tematic studies of this effect have been relatively rare. Herein, we report an effort toward correcting this deficiency by investigating the effect of nitrate on water oxidation catalyzed by IrO x . The results show that nitrate can suppress the reaction, resulting in a decrease of the rate and an increase in the Tafel slope. The effect was found to be consistent with a microkinetic model incorporating competitive adsorption between reac-tion intermediates and nitrate, suggesting that the reaction mechanism was unaffected by anion identity. Moreover, this blocking effect exhibited dependence on the cations, following a trend Li + ≈ Na + ≈ K + > Cs + > TEA + . The results are expected to find broad applications in electrocatalysis.

Tafel slope analysis↗
DOE OSTI2018

Spatially Nonuniform Reaction Rates during Selective Oxidation on Gold

Here, the nonuniform reactivity of adsorbed oxygen during the selective oxidation of methanol on Au(110)-(1×2) was demonstrated using in situ scanning tunneling microscopy (STM), establishing the importance of both atomic and mesoscale structure in determining reaction kinetics. At coverages above 0.06 ML, oxygen consumption occurs preferentially along [$1\overline{10}$] direction, creating local regions completely devoid of oxygen between oxygen islands. The directionally specific reactivity is attributed to a combination of the weaker binding of oxygen atoms at chain termini and the release of surface strain induced by O bonding to Au. The generality of this phenomenon is illustrated by analogous, but kinetically contrasting behavior, for reaction of 2-propanol with oxygen covered Au(110)-(1×2). Even at low O coverages, there are structurally related changes in the reactivity for the reaction with methanol. With decreasing O coverage, a slow reaction period is followed by a fast reaction period, the latter starting when oxygen coverage decreases to ~0.06 monolayer, independent of the initial coverage. This increase in reactivity is attributed to a sudden destabilization of the island structure. These findings demonstrate that both local and mesocale structures can affect reactivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Unlocking anionic redox activity in O3-type sodium 3 d layered oxides via Li substitution

Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes. Here, we report an O3-type NaLi 1/3 Mn 2/3 O 2 phase showing anionic redox activity, obtained through a ceramic process by carefully adjusting synthesis conditions and stoichiometry. This phase shows a sustained reversible capacity of 190 mAh g -1 that is rooted in cumulative oxygen and manganese redox processes as deduced by combined spectroscopy techniques. Unlike many other anionic redox layered oxides so far reported, O3-NaLi 1/3 Mn 2/3 O 2 electrodes do not show discernible voltage fade on cycling. This finding, rationalized by density functional theory, sheds light on the role of inter- versus intralayer 3d cationic migration in ruling voltage fade in anionic redox electrodes. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Altogether, this work offers future directions towards designing highly performing sodium electrodes for advanced Na-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Boosting solid oxide fuel cell performance via electrolyte thickness reduction and cathode infiltration

Increasing the power density and reducing the operating temperature of solid oxide fuel cells (SOFCs) is important for improving commercial viability. Here we discuss two strategies for achieving such improvements in Ni–YSZ supported SOFCs – electrolyte thickness reduction and cathode infiltration. Microstructural and electrochemical results are presented showing the effect of reducing YSZ/GDC electrolyte thickness from 8 to 2.5 μm, and the effect of PrO x infiltration into the LSCF–GDC cathode. Both of these measures are effective, particularly at lower temperatures, leading to an increase in the maximum power density at 650 °C from 0.4 to 0.95 W cm –2 , for example. Electrochemical impedance spectroscopy utilizing subtractive analysis shows that PrO x enhances the cathode charge transfer process. Reducing the electrolyte thickness reduces not only the cell ohmic resistance but also the electrode polarization resistance. Furthermore, the latter effect appears to be an artifact associated with a slight increase in the steam partial pressure at the anode due to minor gas leakage across the thinner electrolyte.

25 ENERGY STORAGE↗