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Zapata J.,Catalan Institute of Nanoscience and Nanotechnology | Burriel M.,Imperial College London | Garcia P.,Catalan Institute of Nanoscience and Nanotechnology | Kilner J.A.,Imperial College London | And 2 more authors.
Journal of Materials Chemistry A | Year: 2013

The layered structure of the orthorhombic GdBaCo2O 5+δ (GBCO) double perovskite compound, currently considered as a promising cathode material in Solid Oxide Fuel Cells (SOFCs), is believed to induce a high degree of anisotropy in the oxygen diffusion coefficient, being maximum along the a-b plane in comparison to the diffusion along the c-axis direction. In this study we have deposited films with different orientation: pure c-axis and a-axis orientation on SrTiO3(001) and NdGaO 3(110) single crystals, respectively. The oxygen diffusion was analysed by isotopic 18O exchange depth profiling (IEDP) and Time-of-flight Secondary Ion Mass Spectrometry (ToF-SIMS) in the films along the longitudinal and transverse directions at different exchange temperatures and exposure times. The magnitude of longitudinal D* at low temperatures shows a clear anisotropy. The oxygen diffusion along the a-axis shows comparable values to the bulk polycrystalline GBCO, while it is about one order of magnitude lower along the c-axis of the structure. The corresponding oxygen surface exchange rates k* do not show any anisotropy having comparable values for c-axis and a-axis orientation. These k* values are slightly larger than those reported for bulk material showing that thin film textured cathodes may have enhanced activity for oxygen reduction at low temperatures. This journal is © The Royal Society of Chemistry 2013.

News Article | December 16, 2016
Site: www.eurekalert.org

Fukuoka, Japan - A potential solution for addressing climate change is to securely store carbon dioxide underground in reservoirs from which oil was previously extracted, an approach known as carbon sequestration. This is expensive, but the costs can be reduced by extracting any remaining oil from these reservoirs at the same time as introducing the carbon dioxide. However, it has been difficult to determine the most appropriate sites in terms of retaining the carbon dioxide for a long time as well as maximizing the recovery of oil. Research from the International Institute for Carbon Neutral Energy Research (I2CNER) at Japan's Kyushu University has now developed a method of simulating a high-pressure mixture of oil, carbon dioxide, and water underground and the extent that it permeates rock, based on images of the rock structure taken at the microscopic level. This approach should help in identifying appropriate sites for applying this technology, thereby increasing the amount of carbon dioxide that can be sequestered and helping impede climate change. For carbon sequestration at sites of spent oil reservoirs, carbon dioxide is injected at such a high pressure that it adopts a fluid-like form called supercritical fluid. There are thus three "fluids": carbon dioxide, water, and oil, at these underground sites, so it is difficult to model their complex behavior. In their study, the researchers used a model called the three-phase lattice-Boltzmann model to predict what will happen to these liquids during carbon sequestration, considering factors such as the size and shapes of empty "pores" within the rock and the levels of saturation of these fluids in the rock. This approach further provides the three-phase relative permeability of natural rocks, although laboratory measurements of this are extremely complicated, costly, and time-consuming. "In carbon sequestration, we can redirect carbon dioxide from sites of major production such as power plants to underground reservoirs, where it should remain for thousands of years," study coauthor Takeshi Tsuji says. "Our method can tell us which storage sites would be best for this. It does this by revealing how much carbon dioxide and oil will pass through the rock at a particular site." Tsuji and author Fei Jiang confirmed the accuracy of this method by testing it with a 3D image of the microstructure of sandstone. The simulation involved setting initial conditions with oil and water present at different levels in the rock, followed by the injection of carbon dioxide at high pressure, after which the changes in the distributions of these three components were predicted. Previous studies were unable to perform such three-phase fluid flow simulation in 3D natural sandstone; therefore this successful simulation in natural rock is an exciting achievement. "The accuracy of the results of our method is very important," Jiang says. "If carbon sequestration practitioners make wrong calculations and choose inappropriate sites, carbon dioxide cannot pass through the rock, and fractures could appear in the rock after the high-pressure injection, which might lead to dangerous emissions at the surface or trigger earthquakes." By improving the efficiency of oil extraction and thus increasing the profitability of this form of carbon sequestration, this method should enable this form of carbon capture to be performed more widely. The article "Estimation of three-phase relative permeability by simulating fluid dynamics directly on rock-microstructure images" was published in Water Resources Research at DOI: 10.1002/2016WR019098.

Apgar B.A.,University of Illinois at Urbana - Champaign | Martin L.W.,International Institute for Carbon Neutral Energy Research
Crystal Growth and Design | Year: 2014

We explore the evolution of epitaxial TiO2 films on a wide range of (001)-oriented perovskite substrates. We observe epitaxial stabilization of anatase to >150 °C above the bulk anatase-to-rutile transition temperature for films grown on substrates with -2.0% to 6.0% lattice mismatch. Continuum elastic models are used to calculate the strain energy density and to construct a model for the preferred epitaxial orientation of anatase. This model is consistent with experimental observations that the strain energy density dominates and leads to the stabilization of 00l- and h00-oriented anatase below and above lattice mismatch values of 5%, respectively. Additionally, TiO 2 nanocrystallite size is found to decrease with lattice mismatch and is discussed in terms of energy competition and possible changes in the nucleation and growth process. To further probe the competition between bulk free, surface, interface, and strain energies in metastable (kinetically limited) as-grown TiO2 films, ex post facto annealing was completed to assess the equilibrium state of the films. These studies confirm the continuum elastic model and highlight the relative importance of the different energies. We then implement our understanding of energy competition to deterministically increase surface area and enhance light absorption via in situ growth processes and ex post facto annealing. © 2014 American Chemical Society.

Apgar B.A.,University of Illinois at Urbana - Champaign | Apgar B.A.,International Institute for Carbon Neutral Energy Research | Lee S.,University of Illinois at Urbana - Champaign | Lee S.,International Institute for Carbon Neutral Energy Research | And 4 more authors.
Advanced Materials | Year: 2013

n-n Schottky, n-n ohmic, and p-n Schottky heterojunctions based on TiO 2/correlated "metallic" oxide couples exhibit strong solar-light absorption driven by the unique electronic structure of the "metallic" oxides. Photovoltaic and photocatalytic responses are driven by hot electron injection from the "metallic" oxide into the TiO2, enabling new modalities of operation for energy systems. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lee S.,University of Illinois at Urbana - Champaign | Lee S.,International Institute for Carbon Neutral Energy Research | Apgar B.A.,University of Illinois at Urbana - Champaign | Apgar B.A.,International Institute for Carbon Neutral Energy Research | And 2 more authors.
Advanced Energy Materials | Year: 2013

Correlated electron oxides prove a diverse landscape of exotic materials' phenomena and properties. One example of such a correlated oxide material is strontium ruthenate (SrRuO3) which is known to be a metallic itinerant ferromagnet and for its widespread utility as a conducting electrode in oxide heterostructures. We observe that the complex electronic structure of SrRuO3 is also responsible for unexpected optical properties including high absorption across the visible spectrum (commensurate with a low band gap semiconductor) and remarkably low reflection compared to traditional metals. By coupling this material to a wide band gap semiconductor (TiO 2) we demonstrate dramatically enhanced visible light absorption and large photocatalytic activities. The devices function by photo-excited hot-carrier injection from the SrRuO3 to the TiO2 and the effect is enhanced in thin films due to electronic structure changes. This observation provides an exciting new approach to the challenge of designing visible-light photosensitive materials. The correlated electron "metal" SrRuO3 exhibits strong visible light absorption. Overlaid on the AM1.5G solar spectrum, it can be seen that SrRuO3 absorbs more than 75 times more light than TiO2. The structural, chemical, and electronic compatibility of TiO2 and SrRuO3 further enables the fabrication of heterojunctions with exciting photovoltaic and photocatalytic response driven by hot-carrier injection. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wilson R.B.,Urbana University | Apgar B.A.,Urbana University | Apgar B.A.,University of California at Berkeley | Apgar B.A.,International Institute for Carbon Neutral Energy Research | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We report the results of time-domain thermoreflectance (TDTR) measurements of two strongly bonded metal-oxide systems with unusually large thermal conductances. We find that TDTR data for the epitaxial SrRuO3/SrTiO3 interface is consistent with an interface conductance G>0.8GWm-2K-1. For an Al/MgO interface at a pressure of 60 GPa, we find G≈1.1GWm-2K-1. Both are within 40% of the maximum possible conductance for these systems, as predicted by simple theory. © 2015 American Physical Society.

Oishi J.,University of Tokyo | Otomo J.,University of Tokyo | Oshima Y.,University of Tokyo | Koyama M.,Kyushu University | And 2 more authors.
Journal of Power Sources | Year: 2015

It is known that the minor elements affect the performance of solid oxide fuel cell (SOFC). In this study, we focus on the influence of minor elements on the SOFC cathode properties. The Ca, Ba, Al, and Si, which originate from raw materials and production processes for SOFC cathodes, are investigated as minor elements that may have effect on the properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode. To examine the effects of minor elements on the cathode properties, Ca, Ba, Al, and Si with a controlled concentration are added to the LSCF reference sample. Conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and surface exchange coefficient (ktr), which governs the overpotential characteristics of the LSCF cathode. The results show that Al and Si have negative effects on both Dchem and ktr while Ca and Ba do not alter Dchem and show weakly positive effects on ktr. The effects of Ca and Ba for the cathode properties are discussed on the basis of XPS measurements. © 2014 Elsevier B.V. All rights reserved.

Otsu T.,Kurume National College of Technology | Tanaka H.,Kyushu University | Sugimura J.,International Institute for Carbon Neutral Energy Research
Toraibarojisuto/Journal of Japanese Society of Tribologists | Year: 2014

This paper describes the effect of surrounding temperature on the behavior of cavitation formed in lubrication film. Point contact sliding tests were conducted in the vacuum chamber in which surrounding temperature and gas were controlled. Temperatures used in this study were in the range between 295 K and 350 K, and gases used were helium, argon, carbon dioxide and air. Two stage cavity growths, i.e. initial stage and second stage as reported in previous report, was found at elevated temperature. Although cavity length was not changed by temperature at initial time after its generation, the cavity length at higher temperature was longer than that at lower temperature in the second stage. Cavity growth in the second stage is affected by gas solubility; cavity length in temperature with higher gas solubility is longer. These results suggest that cavity growth in initial stage is related with rapid evolution of negative pressure at outlet of conjunction and that in second stage is related with gradual release of dissolved gas into cavity.

Mishima F.,Kyushu University | Liu J.,Kyushu University | Kondou C.,Kyushu University | Koyama S.,Kyushu University | Koyama S.,International Institute for Carbon Neutral Energy Research
ACRA 2014 - Proceedings of the 7th Asian Conference on Refrigeration and Air Conditioning | Year: 2014

Low GWP refrigerants R1234ze(Z) and R1234ze(E) are anticipated to being potential refrigerants in high-temperature heat pump systems. This study presents flow boiling heat transfer coefficient and pressure gradient in a horizontal micro-fin tube of 5.35 mm ID at higher temperatures for these new refrigerants and conventional refrigerant R134a. The experiments were conducted at a saturation temperature of 30 °C, mass velocities from 100 to 400 kg m-2s-1, and heat fluxes from 5 to 15 kW m-2. The measured heat transfer coefficient (HTC) and pressure gradient of R1234ze(Z) are higher than those of R134a, while the HTC and pressure gradient of R1234ze(E) are as high as those of R134a. The predicted HTC and pressure gradient by selected correlations reasonably agree with the experimental data. The measured circumferential temperature distribution of the tube wall changes the behavior at vapor qualities where the correlations indicate the transition from separated flow to annular flow and the inception of dryout.

Lorenzino P.,CNRS Laboratory for Materials: Engineering and Science | Buffiere J.-Y.,CNRS Laboratory for Materials: Engineering and Science | Okazaki S.,Kyushu University | Matsunaga H.,Kyushu University | And 2 more authors.
Frattura ed Integrita Strutturale | Year: 2015

High resolution synchrotron X-ray tomography has been used to obtain 3D images of arrested cracks initiated at small artificial defects located on the surface of cylindrical steel specimens subjected to mode I fatigue loading. These defects consist in small semi-circular slits tilted at 0°, 30° or 60° with respect to the plane normal to the loading axis; all of them had the same defect size, √area = 188 μm, where the area denotes the area of the domain defined by projecting the defect on a plane normal to the loading axis. Arrested cracks initiated from the notch were observed for all tilt angles at the surface of samples cycled at the fatigue limit (stress amplitude at which the specimen does not fail after 1×107 cycles). High resolution synchrotron X-ray tomography has been used to obtain 3D images of those small defects and non-propagating cracks (NPC). Despite the fact that steel is a highly attenuating material for X rays, high resolution 3D images of the cracks and of the initiating defects were obtained (0.65 μm voxel size). The values of surface crack length measured by tomography are the same as those obtained by optical microscope measurements. The √area values present the same tendency as the surface length of NPC, i.e. larger non-propagating cracks areas were observed in the softer steel. In the extreme case of 60° tilted defect, the crack fronts appear much more discontinuous with several cracks propagating in mode I until arrest. © 2015, Gruppo Italiano Frattura. All rights reserved.

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