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At least 235 records · Page 13

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DOE OSTI2016

An operationally flexible fuel cell based on quaternary ammonium-biphosphate ion pairs

Here, fuel cells are promising devices for clean power generation in a variety of economically and environmentally significant applications. Low-temperature proton exchange membrane (PEM) fuel cells utilizing Nafion require a high level of hydration, which limits the operating temperature to less than 100°C. In contrast, high-temperature PEM fuel cells utilizing phosphoric acid-doped polybenzimidazole can operate effectively up to 180°C; however, these devices degrade when exposed to water below 140°C. Here we present a different class of PEM fuel cells based on quaternary ammonium-biphosphate ion pairs that can operate under conditions unattainable with existing fuel cell technologies. These fuel cells exhibit stable performance at 80–160°C with a conductivity decay rate more than three orders of magnitude lower than that of a commercial high-temperature PEM fuel cell. By increasing the operational flexibility, this class of fuel cell can simplify the requirements for heat and water management, and potentially reduce the costs associated with the existing fully functional fuel cell systems.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2015

A metal-insulator-metal electron emitter based on a porous Al{sub 2}O{sub 3} film

A metal-insulator-metal electron emitter containing a sandwiched insulator layer composed of porous aluminum oxide Al{sub 2}O{sub 3} was fabricated. The electron emission characteristics of the electron emitter were investigated under vacuum and xenon. Treatment with H{sub 3}PO{sub 4} and rapid thermal oxidation increased the electric field inside the insulator and improved the quality of porous Al{sub 2}O{sub 3}, resulting in higher efficiency and less fluctuation of electron emission. The maximum current and efficiency of electron emission reached 1.05 mA/cm{sup 2} and 51.2%, respectively, under a pressure of 1.0×10{sup −4} Pa. In addition, electrons were injected into xenon and 147 nm vacuum ultraviolet emission was detected in xenon at a pressure of 5.0 × 10{sup 2 }Pa. This electron emitter has a great potential for use as an ultraviolet radiation source.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Morphology and conductivity study of solid electrolyte Li{sub 3}PO{sub 4}

The comparison between two different methods of synthesize of solid electrolyte Li{sub 3}PO{sub 4} as precursor material for developing lithium ion battery, has been performed. The first method is to synthesize Li{sub 3}PO{sub 4} prepared by wet chemical reaction from LiOH and H{sub 3}PO{sub 4} which provide facile, abundant available resource, low cost, and low toxicity. The second method is solid state reaction prepared by Li{sub 2}CO{sub 3} and NH{sub 4}H{sub 2}PO{sub 4.} In addition, the possible morphology identification of comparison between two different methods will also be discussed. The composition, morphology, and additional identification phase and another compound of Li{sub 3}PO{sub 4} powder products from two different reaction are characterized by SEM, EDS, and EIS. The Li{sub 3}PO{sub 4} powder produced from wet reaction and solid state reaction have an average diameter of 0.834 – 7.81 µm and 2.15 – 17.3 µm, respectively. The density of Li{sub 3}PO{sub 4} prepared by wet chemical reaction is 2.238 gr/cm{sup 3}, little bit lower than the sample prepared by solid state reaction which density is 2.3560 gr/cm{sup 3}. The EIS measurement result shows that the conductivity of Li{sub 3}PO{sub 4} is 1.7 x 10{sup −9} S.cm{sup −1} for wet chemical reaction and 1.8 x 10{sup −10} S.cm{sup −1} for solid state reaction. The conductivity of Li{sub 3}PO{sub 4} is not quite different between those two samples even though they were prepared by different method of synthesize.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Biochemical and structural characterizations of two Dictyostelium cellobiohydrolases from the amoebozoa kingdom reveal a high level of conservation between distant phylogenetic trees of life

Glycoside hydrolase family 7 (GH7) cellobiohydrolases (CBHs) are enzymes often employed in plant cell wall degradation across eukaryotic kingdoms of life, as they provide significant hydrolytic potential in cellulose turnover. To date, many fungal GH7 CBHs have been examined, yet many questions regarding structure-activity relationships in these important natural and commercial enzymes remain. Here, we present the crystal structures and a biochemical analysis of two GH7 CBHs from social amoeba: Dictyostelium discoideum Cel7A (DdiCel7A) and Dictyostelium purpureum Cel7A (DpuCel7A). DdiCel7A and DpuCel7A natively consist of a catalytic domain and do not exhibit a carbohydrate-binding module (CBM). The structures of DdiCel7A and DpuCel7A, resolved to 2.1 Å and 2.7 Å, respectively, are homologous to those of other GH7 CBHs with an enclosed active-site tunnel. Two primary differences between the Dictyostelium CBHs and the archetypal model GH7 CBH, Trichoderma reesei Cel7A (TreCel7A), occur near the hydrolytic active site and the product-binding sites. To compare the activities of these enzymes with the activity of TreCel7A, the family 1 TreCel7A CBM and linker were added to the C terminus of each of the Dictyostelium enzymes, creating DdiCel7A CBM and DpuCel7A CBM , which were recombinantly expressed in T. reesei. DdiCel7A CBM and DpuCel7A CBM hydrolyzed Avicel, pretreated corn stover, and phosphoric acid-swollen cellulose as efficiently as TreCel7A when hydrolysis was compared at their temperature optima. The K i of cellobiose was significantly higher for DdiCel7A CBM and DpuCel7A CBM than for TreCel7A: 205, 130, and 29 μM, respectively. Finally, taken together, the present study highlights the remarkable degree of conservation of the activity of these key natural and industrial enzymes across quite distant phylogenetic trees of life.

09 BIOMASS FUELS↗

DOE OSTI2014

Engineering yeast consortia for surface-display of complex cellulosome structures

As our society marches toward a more technologically advanced future, energy and environmental sustainability are some of the most challenging problems we face today. Biomass is one of the most abundant renewable-feedstock for sustainable production of biofuels. However, the main technological obstacle to more widespread uses of this resource is the lack of low-cost technologies to overcome the recalcitrant nature of the cellulosic structure, especially the hydrolysis step on highly ordered celluloses. In this proposal, we successfully engineered several efficient and inexpensive whole-cell biocatalysts in an effort to produce economically compatible and sustainable biofuels, namely cellulosic ethanol. Our approach was to display of a highly efficient cellulolytic enzyme complex, named cellulosome, on the surface of a historical ethanol producer Saccharomyces cerevisiae for the simultaneous and synergistic saccharification and fermentation of cellulose to ethanol. We first demonstrated the feasibility of assembling a mini-cellulosome by incubating E. coli lysates expressing three different cellulases. Resting cells displaying mini-cellulosomes produced 4-fold more ethanol from phosphoric acid-swollen cellulose (PASC) than cultures with only added enzymes. The flexibility to assemble the mini-cellulosome structure was further demonstrated using a synthetic yeast consortium through intracellular complementation. Direct ethanol production from PASC was demonstrated with resting cell cultures. To create a microorganism suitable for a more cost-effective process, called consolidated bioprocessing (CBP), a synthetic consortium capable of displaying mini-cellulosomes on the cell surface via intercellular complementation was created. To further improve the efficiency, a new adaptive strategy of employing anchoring and adaptor scaffoldins to amplify the number of enzymatic subunits was developed, resulting in the creation of an artificial tetravalent cellulosome on the yeast surface and a significant improvement in cellulosic ethanol production. Although this adaptive strategy is ideal for assembling more complex cellulosome for large-scale production of cellulosic ethanol, a substantially larger number of enzymes (up to 10 to 12) is needed to better mimic the natural cellulosome structures for practical usage of the technology.

09 BIOMASS FUELS↗

DOE OSTI2020

Proton exchange membrane fuel cells

Disclosed embodiments concern a membrane electrode assembly or a proton exchange membrane fuel cell comprising a phosphoric acid-doped polymeric membrane comprising a cationic functional group, such as an assembly or fuel cell having an ion exchange capacity of 0.8 to 3 mmol/gram and an operating temperature range of from 80° C. to 220° C. The cationic functional group can be any suitable functional group, such as ammonium, imidazolium, guanidinium, phosphazenium, sulfonium, oxonium, and phosphonium, with working embodiments typically using quaternary ammonium cationic functional groups tethered to the polymeric core. The polymeric material may be any suitable polymeric material, such as a material selected from polyaryl polymers, polyarylamides, polyimides, polystyrenes, polysulfones, polyethers, polyether sulfones, polyketones, polyetherketones, polyarylethers, polyolefins, and polynitriles. The membrane electrode assembly or a proton exchange membrane fuel cell can be used in any application now known or hereafter developed, such as a vehicle or a stationary power device.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2023

Retrofitting of carbon-supported bimetallic Ni-based catalysts by phosphorization for hydrogen evolution reaction in acidic media

Commercial bimetallic Ni–Mo and Ni–Re electrocatalysts supported on advanced conductive carbon are high-performing materials for H 2 evolution reaction in alkaline medium, but they cannot be applied in acidic medium due to the rapid dissolution of metals. Here, in this work, we solve this issue by introducing a convenient phosphorization protocol to convert these commercial metallic electrocatalysts into the respective phosphides, rendering them stable under acidic conditions, and thus providing a pathway to electrocatalysts for water reduction in acidic electrolyte. The novel materials demonstrate high performance, as reflected by the measured low overpotentials, shallow Tafel slopes, fast kinetics, as well as excellent stability and durability. This work opens the possibility to expand the applicability of commercial supported metallic catalysts and electrocatalysts through retrofitting via phosphorization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Quantification of uranium metal and total uranium in U-UO 2 mixtures using H 3 PO 4 -HCl

Here, the selective dissolution of uranium metal from its mixtures with UO 2 was studied to establish a simple and rapid quantitative method. Uranium metal was found to selectively dissolve as U(IV) into a solution of phosphoric and hydrochloric acids, with quantitative dissolution occurring within 1 h. Total dissolution of uranium as U(VI) could then be obtained by nitric acid addition and heating for 0.5–1 h. Analysis of the resulting U(IV) and U(VI) solutions by ICP-OES or UV–Vis spectroscopy yielded uranium metal-to-UO 2 ratios with an accuracy of ± 10% or better. Accuracy of the ICP-OES method was slightly better than UV–Vis, but the simplicity of the latter makes it an attractive option for some applications.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Aerosol Synthesis of Highly Dispersed Y{sub 3}Al{sub 5}O{sub 12}:Ce{sup 3+} Phosphor with Intense Photoluminescence

A simple method of pyrolysis of an aerosol solution of yttrium, aluminum, and cerium nitrates with the addition of urea or citric acid, followed by brief annealing, is developed to obtain a highly dispersed aluminum–yttrium garnet powder that demonstrates intense photoluminescence in the visible light region. Characterization of the synthesized samples (photoluminescence spectra, X-ray diffraction analysis, Raman spectra) showed that intense photoluminescence is achieved only in a narrow window of process conditions, namely, the concentration of nitrate solution and the concentration of citric acid or urea. The photoluminescence intensity increases upon annealing synchronously with an increase in the crystallite size, which, along with the optimal cerium concentration (~0.5 at %), is a determining factor for obtaining high-quality samples. The synthesized powders had intense photoluminescence and high optical perfection, as evidenced by the observation of whispering gallery modes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Probing the Effects of Acid Electrolyte Anions on Electrocatalyst Activity and Selectivity for the Oxygen Reduction Reaction

The local microenvironment at the electrode-electrolyte interface plays an important role in electrocatalytic performance. Herein, we investigate the effect of acid electrolyte anion identity on the oxygen reduction reaction (ORR) activity and selectivity of smooth Ag and Pd catalyst thin films. Cyclic voltammetry in perchloric, nitric, sulfuric, phosphoric, hydrochloric, and hydrobromic acid, at pH1, reveals that Ag ORR activity trends as follows: HClO 4 >HNO 3 >H 2 SO 4 >H 3 PO 4 >HCl>>HBr, while Pd ORR activity trends as: HClO 4 >H 2 SO 4 >HNO 3 >H 3 PO 4 >HCl>>HBr. Moreover, rotating-ring-disk-electrode selectivity measurements demonstrate enhanced 4 e - selectivity on both Ag and Pd, by up to 35% H 2 O 2 and 10% H 2 O 2 respectively, in HNO 3 compared to in HClO 4 . Relating physics-based modeling and experimental results, we postulate that ORR performance depends greatly on anion-related phenomena in the double layer, for instance competitive adsorption and non-covalent interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Origin of the Hadži ABC structure: An ab initio study

Medium and strong hydrogen bonds are well known to give rise to broad features in the vibrational spectrum often spanning several hundred wavenumbers. In some cases, these features can span over 1000 cm{sup −1} and even contain multiple broad peaks. One class of strongly hydrogen-bonded dimers that includes many different phosphinic, phosphoric, sulfinic, and selenic acid homodimers exhibits a three-peaked structure over 1500 cm{sup −1} broad. This unusual feature is often referred to as the Hadži ABC structure. The origin of this feature has been debated since its discovery in the 1950s. Only a couple of theoretical studies have attempted to interpret the origin of this feature; however, no previous study has been able to reproduce this feature from first principles. Here, we present the first ab initio calculation of the Hadži ABC structure. Using a reduced dimensionality calculation that includes four vibrational modes, we are able to reproduce the three-peak structure and much of the broadness of the feature. Our results indicate that Fermi resonances of the in-plane bend, out-of-plane bend, and combination of these bends play significant roles in explaining this feature. Much of the broadness of the feature and the ability of the OH stretch mode to couple with many overtone bending modes are captured by including an adiabatically separated dimer stretch mode in the model. This mode modulates the distance between the monomer units and accordingly the strength of the hydrogen-bonds causing the OH stretch frequency to shift from 2000 to 3000 cm{sup −1}. Using this model, we were also able to reproduce the vibrational spectrum of the deuterated isotopologue which consists of a single 500 cm{sup −1} broad feature. Whereas previous empirical studies have asserted that Fermi resonances contribute very little to this feature, our study indicates that while not appearing as a separate peak, a Fermi resonance of the in-plane bend contributes substantially to the feature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

{sup 6}LiF oleic acid capped nanoparticles entrapment in siloxanes for thermal neutron detection

The good light output of siloxane based scintillators as displayed under γ-rays and α particles has been exploited here to obtain clear and reliable response toward thermal neutrons. Sensitization towards thermal neutrons has been pursued by adding {sup 6}LiF, in form of nanoparticles. Aiming at the enhancement of compatibility between the inorganic nanoparticles and the low polarity, siloxane based surrounding medium, oleic acid-capped {sup 6}LiF nanoparticles have been synthesized by thermal decomposition of Li trifluoroacetate. Thin pellets siloxane scintillator maintained their optical transmittance up to weight load of 2% of {sup 6}Li. Thin samples with increasing {sup 6}Li concentration and thicker ones with fixed {sup 6}Li amount have been prepared and tested with several sources (α, γ-rays, moderated neutrons). Light output as high as 80% of EJ212 under α irradiation was measured with thin samples, and negligible changes have been observed as a result of {sup 6}LiF addition. In case of thick samples, severe light loss has been observed, as induced by opacity. Nevertheless, thermal neutrons detection has been assessed and the data have been compared with GS20, based on Li glass, taken as a reference material.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Bioleaching of rare earth elements from waste phosphors and cracking catalysts

Four microbial cultures were evaluated for organic acid production and their potential utility for leaching of rare earth elements (REE) from retorted phosphor powder (RPP) and spent fluidized cracking catalyst (FCC). Three of the cultures (2 bacterial, 1 fungal) were isolated from environmental and industrial materials known to contain rare earth elements. The other was the well-known and industrially important bacterium Gluconobacter oxydans. Gluconic acid was the predominant identified organic acid produced by all of the cultures; citric and acetic acid were among the other acids detected. There was also maximum REE leaching by cell free culture supernatants obtained with Gluconobacter and the FCC; 49% of total REE was recovered, with preferential recovery of lanthanum over cerium. The phosphor powder was more difficult to leach; only ~2 % total REE was leached from RPP with Gluconobacter. Tests with the RPP indicated that the extent of REE solubilization was similar whether whole cell cultures or cell-free supernatants were used. However, Gluconobacter cell-free culture supernatants with 10-15 mM gluconic acid outperformed abiotically prepared leaching solutions with 30 mM gluconic acid concentrations. Abiotic tests showed that increasing gluconic acid concentrations increased leaching efficiency; for example, total REE leaching from FCC increased from 24 to 36 to 45% when gluconic acid was increased from 10 to 30 to 90 mM. Our research shows that utilizing microorganisms that produce gluconic acid can result in effective leaching of REE from waste materials, and optimizing gluconic acid production will improve recovery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Polymer compositions and methods

The present invention encompasses polymer compositions comprising aliphatic polycarbonate chains containing functional groups that increase the polymer's ability to wet or adhere to inorganic materials. In certain embodiments, chain ends of the aliphatic polycarbonates are modified to introduce silicon-containing functional groups, boron-containing functional groups, phosphorous-containing functional groups, sulfonic acid groups or carboxylic acid groups.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Polymer compositions and methods

Allen, Scott D.↗

DOE OSTI2015

A high sensitive phosphor for dosimetric applications

In this study a novel TL phosphor CaMg{sub 3}(SO{sub 4}){sub 4}:Dy{sup 3+} was prepared by acid distillation method. The TL response of this phosphor towards γ-rays and carbon ion beam was tested. Good dosimetric glow curve was observed which is stable against both the type of radiations. The CaMg{sub 3}(SO{sub 4}){sub 4}:Dy{sup 3+} phosphor doped with 0.2 mol% of Dy{sup 3+}, irradiated with γ-ray shows nearly equal sensitivity to that of commercially available CaSO{sub 4}:Dy TLD phosphor whereas 3.5 times more sensitivity than CaSO{sub 4}:Dy, when irradiated with carbon ion beam. The change in glow peak intensities and glow peak temperature with variation in irradiation species and energy of ion beam is discussed here. The effect of these on trapping parameters is also illustrated.

61 RADIATION PROTECTION AND DOSIMETRY↗

DOE OSTI2015

Syntheses, structures and tunable luminescence of lanthanide metal-organic frameworks based on azole-containing carboxylic acid ligand

Design and synthesis of a series of isostructural lanthanide metal-organic frameworks (LnMOFs) serving as phosphors by coordinate the H{sub 2}TIPA (5-(1H-tetrazol-5-yl)isophthalic acid) ligands and lanthanide ions is reported. The color of the luminescence can be tuned by adjusting the relative concentration of the lanthanide ions in the host framework GdTIPA, and near-pure-white light emission can be achieved. - Graphical abstract: Lanthanide metal-organic frameworks (LnMOFs) with tunable luminescence were synthesized using an azole-containing carboxylic acid as ligand. - Highlights: • A series of isostructural LnMOFs serving as phosphor is reported. • We model the GdTIPA: Tb{sup 3+}, Eu{sup 3+} which can tune color and emit white light. • The scheme and mechanism of luminescent LnMOFs are also presented and discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Preparation of LaB{sub 3}O{sub 6}:Eu{sup 3+} phosphors by a facile precursor method and their luminescent properties

Graphical abstract: LaB{sub 3}O{sub 6}:Eu{sup 3+} phosphor was obtained by calcining the precursor which was synthesized by boric acid melting method. It (a) exhibits much stronger PL intensity than that (b) prepared by conventional solid state reaction method. - Highlights: • A calcining precursor method was used for preparation of LaB{sub 3}O{sub 6}:Eu{sup 3+} phosphor. • Precursor was prepared by boric acid melting method. • The luminescence intensity of LaB{sub 3}O{sub 6}:Eu{sup 3+} was enhanced by the present method. - Abstract: The LaB{sub 3}O{sub 6}:Eu{sup 3+} phosphors were prepared by calcining the precursors which were synthesized by boric acid melting method using rare earth oxide and boric acid as raw materials, and they were characterized by EDS, XRD, IR, SEM and PL. The influences of reaction temperature for the preparation of precursor and subsequent calcination temperature and time of precursor on the luminescence properties of LaB{sub 3}O{sub 6}:Eu{sup 3+} phosphor were investigated. The results showed that the LaB{sub 3}O{sub 6}:Eu{sup 3+} phosphors with maximum luminescent intensity were obtained by calcining precursor at 1000 °C for 6 h, in which the precursor was prepared at 200 °C for 72 h. Compared with the conventional high temperature solid-state reaction method, the pure LaB{sub 3}O{sub 6}:Eu{sup 3+} phosphor can be obtained at relatively lower calcination temperature by the precursor method and exhibits much stronger emission intensity.

36 MATERIALS SCIENCE↗