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LaCoO 3-δ coated Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ cathode for intermediate temperature solid oxide fuel cells
Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) is a promising cathode for intermediate temperature solid oxide fuel cells. Yet, BSCF cathode performance stability has been a challenge and its electrochemical performance deteriorates severely in the presence of Cr2O3-forming metallic interconnect. We demonstrate that LaCoO 3-δ (LC) coating on BSCF cathode can not only enhance BSCF electrochemical performance, but also effectively improve the BSCF performance stability. Here, LC-coated BSCF-Gd 0.1 Ce 0.9 O 1.9 (LC@BSCF-GDC) cathode is prepared through a solution impregnation method and systematically characterized. EIS, XRD, Raman, SEM and EDS tests with and without SUS430 interconnect are conducted to characterize the Cr-tolerance. The results reflect that BSCF-GDC cathode is susceptible to Cr poisoning while LC@BSCF-GDC cathode has significantly enhanced tolerance to Cr poisoning. Single cells with LC@BSCF-GDC cathode achieve higher peak power density and smaller polarization resistance values than that of single cells with BSCF-GDC cathode. Furthermore, significant improvement of performance stability under a constant current load has been achieved for single cells with LC@BSCF-GDC cathode. This work provides a new solution for solving BSCF cathode performance stability.
LaCrO 3 -Coated La 0.6 Sr 0.4 Co 0.2 Fe0.8O3–δ Core–Shell Structured Cathode with Enhanced Cr Tolerance for Intermediate-Temperature Solid Oxide Fuel Cells
La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) is a common cathode material for intermediate temperature solid oxide fuel cells due to its excellent oxygen reduction reaction catalytic activity. However, the Cr-poisoning effect is a severe issue causing its electrochemical performance degrada-tion. To develop a LSCF-based cathode with excellent Cr-tolerance, LaCrO 3 -coated LSCF core-shell structured (LCr@LSCF) cathode was prepared via solution infiltration method. After coated by LCr shell, the long-term stability and Cr-tolerance were obviously improved, at the price of sacrificing some electrochemical performance. As a result, the development of LCr@LSCF cathode with eye-catching Cr-tolerance is of great significance to the commercialization of LSCF.
Methods for producing perovskite-containing devices
The present disclosure relates to a method that includes applying a first perovskite precursor solution to a substrate to form a first liquid film of the first perovskite precursor solution on the substrate; from the first liquid film, forming a first intermediate solid perovskite layer on the substrate; repeating at least once, both the applying and the forming, resulting in the creation of at least one additional intermediate solid perovskite layer; and treating a last intermediate solid perovskite layer, resulting from the at least one additional applying and the at least one additional forming, to create a final solid perovskite layer.
Intermediate Temperature Solid Oxide Cell with a Barrier Layer Free Oxygen Electrode and Phase Inversion Derived Hydrogen Electrode
High-temperature solid oxide cells (SOCs) have fundamental advantages in efficiency and product rate over their low-temperature counterparts. However, the commercial development of SOCs is hindered by cost and reliability. To solve the issues, lowering the operating temperature of SOCs is deemed the best solution. Here we report on our effort toward intermediate temperature (IT) SOCs by developing a barrier layer free high-performance oxygen electrode and open structured hydrogen electrode. The results show that the new oxygen electrode provides reasonably good oxygen electrocatalytic activity at IT range for oxygen reduction and evolution reactions and the open structured hydrogen electrode provides low gas diffusion path for H 2 /H 2 O. However, at high electrolysis current density such as 1 A cm −2 and 650 °C, the present oxygen electrode delaminates after 200 h. The phase-inversion derived open structured hydrogen electrode helps gas diffusion but, in the meantime, reduces reactive sites. A proper balance of porosity and number of reactive sites is still needed for future hydrogen electrode development.
Thermal decomposition of neptunyl ammonium nitrate: mechanistic insights and structural characterization of the Np 2 O 5 intermediate phase
Neptunium (Np) possesses a rich and unique chemistry that often diverges from other actinide elements yet remains relatively underexplored compared with the other light actinides. A resurgence of interest in Np has been spurred by the application of 237 Np for plutonium-238 ( 238 Pu) production for use in radioisotope thermoelectric generators (RTGs), necessitating evaluation of Np chemical reactions and materials. The work presented here studied the thermal decomposition of neptunyl ammonium nitrate (NH 4 Np VI O 2 (NO 3 ) 3 ) for synthesis of neptunium dioxide (NpO 2 ), which is the target material used for production of 238 Pu. Additionally, structural characterization of the intermediate solid Np pentoxide (Np 2 O 5 ) was performed. Advanced solid-state characterization techniques, including simultaneous thermal analysis (STA), powder X-ray diffraction (pXRD), Raman spectroscopy, and density functional theory (DFT) modeling have been combined to study the reaction pathways. Analysis revealed that NH 4 Np VI O 2 (NO 3 ) 3 thermally decomposes to a proposed neptunyl nitrate intermediate, followed by Np 2 O 5 and finally NpO 2 , all within the temperature range of 150 °C–600 °C. Further characterization of the pentoxide intermediate provided the first Raman spectra of pure-phase Np 2 O 5 and associated DFT modeling confirmed Raman peak assignments for this phase. These findings provide mechanistic information to advance production of the critical radioisotope 238 Pu and advance the state of knowledge on Np materials chemistry using modern characterization techniques.
Reactive Species and Reaction Pathways for the Oxidative Cleavage of 4-Octene and Oleic Acid with H 2 O 2 over Tungsten Oxide Catalysts
The oxidative cleavage of carbon-carbon double bonds (C=C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, non-toxic, and selective for the oxidative cleavage of C=C bonds with hydrogen peroxide (H 2 O 2 ) and are, therefore, a promising option for continuous processes. Despite the relevance of these materials, the elementary steps involved and their sensitivity to the form of W sites present on surfaces have not been described. In this work, we combine in situ spectroscopy and rate measurements to identify significant steps in the reaction, the reactive species present on catalysts, and examine differences between the kinetics of this reaction on isolated W atoms grafted to alumina and on those exposed on crystalline WO 3 nanoparticles. Raman spectroscopy shows that W-peroxo complexes (W-(η 2 -O 2 ) formed from H 2 O 2 ) react in a kinetically relevant step to produce epoxides, which undergo hydrolysis at protic surface sites. Subsequently, the CH 3 CN solvent deprotonates diols to form alpha hydroxy ketones that react to form aldehydes and water following nucleophilic attack of H 2 O 2 . Turnover rates for oxidative cleavage, determined by in situ site titrations, on WO x -Al 2 O 3 are 75% greater than those on WO 3 at standard conditions. These differences reflect activation enthalpies (ΔH ‡ ) for oxidative cleavage of 4-octene that are much lower for the isolated WO x sites (36±3 and 60±6 kJ∙mol -1 for WO x -Al 2 O 3 and WO 3 , respectively) and correlate strongly with the difference between enthalpies of adsorption for epoxyoctane (ΔH ads,epox ), which resembles the transition state for epoxidation. The WO x -Al 2 O 3 catalysts mediate oxidative cleavage of oleic acid with H 2 O 2 following a mechanism comparable to that for 4-octene. The WO 3 materials, however, form only the epoxide and do not cleave the C-C bond or produce aldehydes and acids. These differences reflect the distinct site requirements for these reaction pathways and indicate that acid sites required for diol formation are strongly inhibited by oleic acids and epoxides on WO 3 whereas the Al 2 O 3 support provides sites competent for this reaction and increase the yield of the oxidative cleavage products.
Liquid crystalline behavior and photoluminescence of lanthanide decanoate nanoparticles synthesized by microwave radiation
Luminescent lanthanide decanoate nanoparticles (LnC 10 NPs; Ln = Pr, Nd, Sm, Eu, Gd, Er) with spherical morphology (<100 nm) have been synthesized via a facile microwave (MWV) method using Ln(NO 3 ) 3 ·xH 2 O, ethanol/water, and decanoic acid. These hybrid nanomaterials adopt a lamellar structure consisting of inorganic Ln 3+ layers separated by a decanoate anion bilayer and exhibit liquid crystalline (LC) phases during melting. The particle size, crystalline structure, and LC behavior were characterized using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (ambient and heated). Thermal analysis indicated the formation of Smectic A LC phases by LnC 10 nanoparticles, with the smaller lanthanides (Ln = Sm, Gd, Er) displaying additional solid intermediate and Smectic C phases. The formation of LC phases by the smaller Ln 3+ suggests that these nanoscale materials have vastly different thermal properties than their bulk counterparts, which do not exhibit LC behavior. In this work, photoluminescence spectroscopy revealed the LnC 10 NPs to be highly optically active, producing strong visible emissions that corresponded to expected electronic transitions by the various Ln 3+ ions. Under long-wave UV irradiation (λ = 365 nm), bright visible luminescence was observed for colloidal suspensions of Nd, Sm, Eu, Gd, and ErC 10 NPs. To the best of the authors’ knowledge, this is the first reported synthesis of nanoscale metal alkanoates, the first report of liquid crystalline behavior by any decanoate of lanthanides smaller than Nd, and the first observation of strong visible luminescence by non-vitrified lanthanide alkanoates.
Reduction of Np(v) to Np(iv) using oxalic acid: rethinking decades of nuclear processing conventions
Actinide oxalate precipitation has been ubiquitous in nuclear processing since the 1950s due to its simplicity at laboratory and production scales as both a means of actinide purification and as a key intermediate solid phase towards oxide production. Historical processing information has emphasized the need to reduce actinides, including neptunium (Np), to the tetravalent or trivalent state with chemical reducing agents prior to oxalate precipitation. This work revisits the established method and reveals that oxalic acid has an unexpected role as a reducing agent for Np(v/vi). Also, the study uncovers insights into the direct precipitation of Np(iv) oxalate from neptunyl solutions, as identified by spectroscopic and X-ray diffraction analyses. These findings challenge the long-standing notion that redox adjustment of actinides is necessary for oxalate processing.
X-ray tracking of structural changes during a subnanosecond solid-solid phase transition in cobalt nanoparticles
This work presents measurements of laser-induced solid-solid phase transitions in Co nanoparticles, using time-resolved wide-angle x-ray scattering with <100-ps time resolution. A comparison of the experimental results with scattering simulations indicates a phase transition from the as-synthesized ε phase into a mixed phase of 2/3 hcp and 1/3 fcc character during the first 100 ps. The measured scattering signal observed at the shortest investigated time delay of 20 ps has less scattering intensity at the dominant fcc/hcp Bragg peak positions compared to the difference signal acquired at 100 ps. This suggests the formation of a partially disordered solid intermediate phase on the sub-100-ps timescale.
Data from Reactive Species and Reaction Pathways for the Oxidative Cleavage of 4-Octene and Oleic Acid with H2O2 over Tungsten Oxide Catalysts
Oxidative cleavage of carbon–carbon double bonds (C═C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, nontoxic, and selective for the oxidative cleavage of C═C bonds with hydrogen peroxide (H2O2) and are, therefore, a promising option for continuous processes. Despite the relevance of these materials, the elementary steps involved and their sensitivity to the form of W sites present on surfaces have not been described. Here, we combine in situ spectroscopy and rate measurements to identify significant steps in the reaction and the reactive species present on the catalysts and examine differences between the kinetics of this reaction on isolated W atoms grafted to alumina and on those exposed on crystalline WO3 nanoparticles. Raman spectroscopy shows that W–peroxo complexes (W–(η2-O2)) formed from H2O2 react with alkenes in a kinetically relevant step to produce epoxides, which undergo hydrolysis at protic surface sites. Subsequently, the CH3CN solvent deprotonates diols to form alpha-hydroxy ketones that react to form aldehydes and water following nucleophilic attack of H2O2. Turnover rates for oxidative cleavage, determined by in situ site titrations, on WOx–Al2O3 are 75% greater than those on WO3 at standard conditions. These differences reflect the activation enthalpies (ΔH‡) for the oxidative cleavage of 4-octene that are much lower than those for the isolated WOx sites (36 ± 3 and 60 ± 6 kJ·mol–1 for WOx–Al2O3 and WO3, respectively) and correlate strongly with the difference between the enthalpies of adsorption for epoxyoctane (ΔHads,epox), which resembles the transition state for epoxidation. The WOx–Al2O3 catalysts mediate oxidative cleavage of oleic acid with H2O2 following a mechanism comparable to that for the oxidative cleavage of 4-octene. The WO3 materials, however, form only the epoxide and do not cleave the C–C bond or produce aldehydes and acids. These differences reflect the distinct site requirements for these reaction pathways and indicate that acid sites required for diol formation are strongly inhibited by oleic acids and epoxides on WO3 whereas the Al2O3 support provides sites competent for this reaction and increase the yield of the oxidative cleavage products.
High Momentum Transfer Nucleon Elastic Electromagnetic Form Factor Measurements Using Super BigBite Spectrometer at Jefferson Lab
The nucleons - protons and neutrons - are the basic building blocks of atomic nuclei. We now know that the nucleon consists of fundamental particles called quarks and gluons. The quarks interact with each other by exchanging gluons via the strong interaction. Understanding the quark-gluon structure of the nucleon, especially the confinement of quarks within the nucleon in its ground state, remains one of the main unsolved puzzles of particle physics. The nucleon electromagnetic form factors are directly related to the internal structure of the nucleon. A new generation of high precision experiments, GEp-V, GEn-II, GEn-RP, and GMn, measuring the ground state nucleon space-like electro-magnetic form factor at high momentum transfer is underway at Jefferson Lab experimental Hall-A as part of the Super Bigbite Spectrometer (SBS) program. This series of experiments will provide a new level of understanding of the nucleon structure. These experiments are highly demanding due to the extremely fast drop off of the elastic cross section with the increasing four-momentum transfer squared(Q2). This thesis provides an overview of the SBS physics program and reports on the extensive R&D program carried out to achieve the high rate running conditions essential for carrying out the SBS experiments. SBS will provide an intermediate solid angle of approximately 35 msr, which is significantly larger than the solid angle of other dipole based spectrometers at Jefferson lab. Of course, there are much larger acceptance spectrometers at Jefferson Lab, CLAS12 for example. What is special about SBS is that it provides a sizable acceptance while operating at the highest possible luminosity at Jefferson Lab. With this combination of medium acceptance and the highest available luminosity, SBS provides an unparalleled opportunity to explore the nucleon in its ground state with unprecedented resolution. The relatively large acceptance of SBS is achieved by using a large gap dipole magnet and placing it close to the target. An unavoidable consequence of this is that the SBS GEM trackers and other detectors have a clear line-of-sight view of the target and a portion of the beam-line. As a result, the background hit rate in the SBS front GEM trackers is expected to be up to 500 kHz/cm2, over the entire active area of 6000 cm2. To the best of our knowledge, this extremely high rate over such a large area is unprecedented in any particle tracking system used anywhere in the world before. Correctly reconstructing the particle tracks of interest in this very high background environment is achieved by using especially adapted high rate techniques at every step of the tracking process: optimizing the GEM module and tracker design at the hardware level, using high bandwidth electronics and real time Field Programmable Gate Array (FPGA) based background suppression techniques at the Data Acquisition (DAQ) level, and developing highly specialized tracking algorithms to pick out the signal hits from among the vast amount of background hits. In order to ensure a smooth start and running of the SBS experiments, it is extremely crucial that these techniques are developed, implemented, and tested under realistic conditions well before the actual start of the SBS experimental program. A detailed Geant4 simulation of the experiment was combined with a digitization package to generate the detector level pseudodata similar to what is expected in the actual experiments. The digitization procedures were calibrated against actual GEM data from cosmic-ray runs, X-ray tests, beam test runs in experimental Hall-A, and the PRad experiment in Hall B. Then, optimized tracking algorithms were developed and implemented in an analysis program used to analyze these pseudo-data and to extract expected high-level parameters. These extracted quantities were then compared with the input parameters from the simulation to verify and determine the performance characteristics for the SBS tracker. From this work, a final tracking efficiency of 69% at 25% occupancy was achieved, with the required reconstruction accuracy, for the GMn experiment, the first experiment in the SBS program, with background level at 100 kHz/cm2. These demonstrated parameters are adequate for the successful running of not only the GMn experiment but as well as for GEn-RP and GEn-II experiments, the second and third experiments in the program. This work builds the solid ground to further improve the tracking performance for these experiments and achieve similar conditions for the running of the GEp-V experiment, the most demanding experiment in the SBS program, with an expected background level at 500 kHz/cm2.
Lignocellulosic Processing Stream Analytical: Cooperative Research and Development (Final Report)
The project will determine the detailed composition of process lignocellulosic biomass slurries and solids using NREL’s unique capabilities in the area.
Solid-state organic intermediate-band photovoltaic devices
In one aspect, solid-state organic intermediate-band photovoltaic devices are provided. A solid-state organic intermediate-band photovoltaic device, in some embodiments, comprises an organic electron donor and an organic electron acceptor, wherein the organic electron donor comprises a singlet energy level separated from a triplet energy level by an energy gap. The device also comprises a triplet sensitizer comprising singlet and triplet energy levels falling within the singlet-triplet energy gap of the electron donor.
Solid-state organic intermediate-band photovoltaic devices
In one aspect, solid-state organic intermediate-band photovoltaic devices are provided. A solid-state organic intermediate-band photovoltaic device, in some embodiments, comprises an organic electron donor and an organic electron acceptor, wherein the organic electron donor comprises a singlet energy level separated from a triplet energy level by an energy gap. The device also comprises a triplet sensitizer comprising singlet and triplet energy levels falling within the singlet-triplet energy gap of the electron donor.
Tracking the nanoparticle exsolution/reoxidation processes of Ni-doped SrTi 0.3 Fe 0.7 O 3- δ electrodes for intermediate temperature symmetric solid oxide fuel cells
In situ NAP-XPS and XAS are used to elucidate the mechanisms of the exsolution/reoxidation process in Sr 0.93 Ti 0.3 Fe 0.63 Ni 0.07 O 3 δ (STFN) perovskite, used as an electrode for intermediate temperature-SOFC.
Kinetic Pathways Templated by Low-Temperature Intermediates during Solid-State Synthesis of Layered Oxides
Layered oxides have been the dominant cathodes in lithium-ion batteries, and among them, high-nickel (Ni) systems are attractive because of their high capacity. For practical use, synthetic control of stoichiometry and structural ordering is crucial but has been nontrivial due to the complexity inherent to synthesis reactions, which often proceed via nonequilibrium pathways. In this paper, we report here a combined in situ synchrotron X-ray diffraction and ab initio study of solid-state synthesis of layered oxides starting from acetate precursors for LiCoO 2 and LiNiO 2 and their solid solution LiNi 0.8 Co 0.2 O 2 . While all three systems ultimately evolve into the same thermodynamically stable layered phase ($R\overline{3}m$), each chemistry involves distinct metastable intermediates. We explain the phase progressions using a structural template model, demonstrating that during the synthesis of LiCoO 2 , the formed metastable spinel polymorph (Li 2 Co 2 O 4 ; $Fd\overline{3}m$) is a kinetically facile lithiation product of spinel Co 3 O 4 —the low-temperature (LT) intermediate from the decomposed Co-acetate. Similarly, in the Ni-based systems, the acetate decomposition products, rocksalts (Ni,Co)O, topotactically template the kinetic pathways of forming disordered rocksalts (Li x (Ni,Co) 2–x O 2 ; $Fm\overline{3}m$), consequently leading to off-stoichiometric Li x (Ni,Co)O 2 with undesired high Li/Ni mixing. These findings highlight new opportunities for engineering precursors to form LT intermediates that template the synthesis of target phases and structural properties.
A high-performance intermediate temperature reversible solid oxide cell with a new barrier layer free oxygen electrode
The best solution to address the critical durability issue of solid oxide electrolytic cells (SOECs) for high-efficiency and high-rate H 2 production is to lower the operating temperature without sacrificing the performance. Developing high performance oxygen electrodes (OEs) is a key to capitalizing this solution. Here, in this paper, we report on a highly active OE for intermediate temperature ZrO 2 -based SOECs without a CeO 2 barrier layer. The new barrier-layer-free (BLF) OE is a composite of two materials, (Bi 0.75 Y 0.25 ) 0.93 Ce 0.07 O 1.5±δ (BYC) that exhibits high oxide-ion conductivity and La 0.8 Sr 0.2 MnO 3 (LSM) that possesses a high electronic conductivity to enable fast oxygen reduction/evolution reactions (ORR/OER). Featuring a microscale porous BYC scaffold decorated with high surface area LSM nanoparticles (NPs), the new BLF-OE exhibited a low area specific resistance (ASR) of 0.10 Ω cm 2 at 650 °C in air. With 50%H 2 -50%H 2 O as a feed to hydrogen electrode (HE) and air to OE, the single cell performance achieved 588 mA cm -2 at 0.80 V in the fuel cell mode and 688 mA cm -2 at 1.30 V in the electrolytic mode at 650 °C. Our in-house testing showed that this level of performance was ~3.5x higher than the cell with the benchmark La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ -Ce 0.9 Gd 0.1 O 2-δ OE. The long-term durability testing under alternating fuel cell and electrolytic modes showed a low degradation rate of 0.10 mA cm -2 h -1 over 550 hours. These encouraging results showed the great promise of the newly developed BYC-LSM to be an excellent OE candidate for intermediate temperature SOECs.