Multiscale modeling and its validation of the trans-cis-trans reorientation-based photodeformation in azobenzene-doped liquid crystal polymer

Yun, J.H.,Li, C.,Chung, H.,Choi, J.,Cho, M. Pergamon Press ; Elsevier Science Ltd 2017 International journal of solids and structures Vol.128 No.-

<P>We propose a new model for predicting the trans-cis-trans reorientation (TCTR)-based photodeformation of the azobenzene-doped liquid-crystal polymer (azo-LCP). The model was validated through the results of a bi-directional photobending experiment performed at various temperatures and mole ratios of the azobenzene monomer within the azo-LCP. Through both numerical and experimental investigations, we found that the photobending curvature of the azo-LCP shows a maximum point at certain temperatures, but only shows a proportional relationship with the azobenzene mole ratio within the azo-LCP. We confirmed that this tendency is caused by the change in the polymeric constraint with the temperature and the low light propagation in azo-LCP. (C) 2017 Elsevier Ltd. All rights reserved.</P>

High-performance ceramic composite electrodes for electrochemical hydrogen pump using protonic ceramics

Choi, J.,Shin, M.,Kim, B.,Park, J.S. Pergamon Press ; Elsevier Science Ltd 2017 International journal of hydrogen energy Vol.42 No.18

<P>Ceramic composite electrodes comprising an electron-conducting ceramic (Sr-doped LaVO3), a protonic ceramic [Cu and Y-doped Ba(Ce,Zr)O-3], and small amounts of CeO2 and Pd as catalysts were fabricated using an infiltration method for use in an electrochemical hydrogen pump and the hydrogen fluxes and the faradaic efficiency were measured by analyzing the gas compositions. This composite electrode performed well; the area-specific resistance of the electrode polarization at 1 A cm (2) was just 0.15 Omega cm(2) at 973 K in hydrogen pumping mode, and the overpotential at a large current density of 2 A cm(-2) was only about 1.1 Vat 973 K. To optimize the operating conditions, the effects of the steam vapor pressure and hydrogen partial pressure on the electrochemical performance of the hydrogen pump were investigated. The steam in the sweep side was consumed by the steam electrolysis due to the partial oxygen conductivity. Therefore, supplying insufficient steam to the cathode was found to cause a steep increase in the voltage at high currents owing to a decrease in the proton conductivity. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.</P>

Fabrication of solid oxide fuel cells (SOFCs) by solvent-controlled co-tape casting technique

Lee, S.,Lee, K.,Jang, Y.h.,Bae, J. Pergamon Press ; Elsevier Science Ltd 2017 International journal of hydrogen energy Vol.42 No.3

<P>A co-tape casting process has an advantage of cost-effectiveness for mass production. To fabricate solid oxide fuel cells (SOFCs) with high electrochemical performance by co-tape casting, high solid loading and binder content of tape cast slurry are required to improve particle network strength. However, high solid loading and binder content cause high viscosity of the slurry, which makes removal of air bubbles and handling difficult. In this study, a new method to fabricate uniform green tapes with high solid loading and binder content by controlling solvent ratio under vacuum condition is proposed. As a result, high solid loading and binder content with 39% improved storage shear modulus, 26% improved LVR length, tensile strength of 5.0 MPa, and packing density of 57.5% were achieved at solvent ratio of 22 wt%. To fabricate unit cells using the green tapes, thermal decomposition and shrinkage behavior are characterized, and heat treatment steps at 250 degrees C, 350 degrees C, and 500 degrees C and co-sintering temperature were determined at 1250 degrees C. A fabricated unit cell showed open circuit voltage (OCV) of 1.10 V and the maximum power density of 1.20 W cm(-2) at 800 degrees C. To fabricate crack-free Phi 5.0 cm unit cells, the mechanical strength of the anode support tapes after thermal decomposition was measured to determine the tape compositions that can minimize cracks at the unit cell. As a result, a crack-free unit cell with a diameter of 5.0 cm was fabricated, achieving OCV of 1.05 V and power of 4.3 W at 800 degrees C. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.</P>

Moire superlattices in strained graphene-gold hybrid nanostructures

Palinkas, A.,Sule, P.,Szendro, M.,Molnar, G.,Hwang, C.,Biro, L.P.,Osvath, Z. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.107 No.-

<P>Graphene-metal nanoparticle hybrid materials potentially display not only the unique properties of metal nanoparticles and those of graphene, but also additional novel properties due to the interaction between graphene and nanoparticles. This study shows that gold nanoislands can be used to tailor the local electronic properties of graphene. Graphene on crystalline gold nanoislands exhibits moire superlattices, which generate secondary Dirac points in the local density of states. Conversely, the graphene covered gold regions undergo a polycrystalline -> Au (111) phase transition upon annealing. Moreover, the nanoscale coexistence of moire superlattices with different moire periodicities has also been revealed. Several of these moire periodicities are anomalously large, which cannot be explained by the standard lattice mismatch between the graphene and the topmost Au (111) layers. Density functional theory and molecular dynamics simulations show for the first time that in such cases the graphene and the interfacial metallic layer is strained, leading to distorted lattice constants, and consequently to reduced misfit. Room temperature charge localization induced by a large wavelength moire pattern is also observed by scanning tunneling spectroscopy. These findings can open a route towards the strain engineering of graphene/metal interfaces with various moire superlattices and tailored electronic properties for nanoscale information coding. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential

Kwon, K.D.,Newton, A.G. Pergamon Press ; Elsevier Science Ltd 2016 Geochimica et cosmochimica acta Vol.190 No.-

<P>The surfaces of clay minerals, which are abundant in atmospheric mineral dust, serve as an important medium to catalyze ice nucleation. The lateral edge surface of 2:1 clay minerals is postulated to be a potential site for ice nucleation. However, experimental investigations of the edge surface structure itself have been limited compared to the basal planes of clay minerals. Density functional theory (DFT) computational studies have provided insights into the pyrophyllite edge surface. Pyrophyllite is an ideal surrogate mineral for the edge surfaces of 2: 1 clay minerals as it possesses no or little structural charge. Of the two most-common hydrated edge surfaces, the AC edge, (110) surface in the monoclinic polytype notation, is predicted to be more stable than the B edge, (010) surface. These stabilities, however, were determined based on the total energies calculated at 0 K and did not consider environmental effects such as temperature and humidity. In this study, atomistic thermodynamics based on periodic DFT electronic calculations was applied to examine the effects of environmental variables on the structure and thermodynamic stability of the common edge surfaces in equilibrium with bulk pyrophyllite and water vapor. We demonstrate that the temperature-dependent vibrational energy of sorbed water molecules at the edge surface is a significant component of the surface free energy and cannot be neglected when determining the surface stability of pyrophyllite. The surface free energies were calculated as a function of temperature from 240 to 600 K and water chemical potential corresponding to conditions from ultrahigh vacuum to the saturation vapor pressure of water. We show that at lower water chemical potentials (dry conditions), the AC and B edge surfaces possessed similar stabilities; at higher chemical potentials (humid conditions) the AC edge surface was more stable than the B edge surface. At high temperatures, both surfaces showed similar stabilities regardless of the water chemical potential. The equilibrium morphology of pyrophyllite crystals is also expected to be dependent on these two environmental variables. Surface defects may impact the surface reactivity. We discuss the thermodynamic stability of a possible Si cation vacancy defect which provides additional hydroxyl group on the surface. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Extension of an effective MCFC kinetic model to a wider range of operating conditions

Audasso, E.,Bosio, B.,Nam, S. Pergamon Press ; Elsevier Science Ltd 2016 International journal of hydrogen energy Vol.41 No.12

<P>The aim of this work is to improve the semi-empirical MCFC kinetics model previously developed by the authors for laboratory and industrial simulation to make it applicable to a wider range of feeding compositions. New parameters are taken into account and identified to describe O-2 and cathode induced flux effects, which were neglected in the previous formulation. The newly obtained equation is integrated as kinetic core in the SIMFC (SIMulation of Fuel Cells) code, an MCFC 3D model set up by the UNIGE PERT group, to test its reliability. Validation is performed using experimental data collected through experimental tests carried out at the Fuel Cell Research Centre laboratories of the Korea Institute of Science and Technology (KIST) using 100 cm(2) single cell facilities. The results will be discussed in detail giving examples of the simulated performance varying operating conditions and evaluating the different polarisation contributions. Through the final formulation the average percentage error obtained for all the simulated cases respect to experimental results is maintained around 1% despite the very wide operating range. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.</P>

Genetic variation in a freshwater prawn species, Palaemon paucidens, in South Korea

Song, K.H.,Jung, J.,Kim, W. Pergamon Press ; Elsevier Science Ltd 2016 Biochemical systematics and ecology Vol.65 No.-

<P>The biogeography of freshwater biota in the Korean Peninsula has been affected by recent geological processes and anthropogenic activity. The freshwater prawn, Palaemon paucidens, can serve as a non-fish model organism suitable for assessing these factors, as it is found in all river systems in the Korean Peninsula and may have been introduced by humans in some regions. In this study, we investigated the geographical distribution of genetic variation and the genetic structure of P. paucidens populations using mitochondrial DNA sequences and genotypes identified from four microsatellite loci. Our results showed that populations from westward-flowing river systems that drain into the Yellow Sea have more genetic diversity than those from southward-flowing river systems, and that the highest genetic variance revealed by analysis of molecular variance (AMOVA) using both genetic markers was observed in river systems grouped as HAN + GEUM, NAKDONG + JEJU, YOUNGSAN, and SEOMJIN. These results suggest that HAN and GEUM, in which freshwater prawn populations have higher levels of genetic diversity, were the most recently isolated river systems from Asian continental systems. Therefore, populations from HAN and GEUM experienced less severe bottlenecks than those from YOUNGSAN and SEOMJIN. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Hydrogen production by steam reforming of ethanol over mesoporous Cu-Ni-Al₂O₃-ZrO₂ xerogel catalysts

Han, S.J.,Song, J.H.,Bang, Y.,Yoo, J.,Park, S.,Kang, K.H.,Song, I.K. Pergamon Press ; Elsevier Science Ltd 2016 International journal of hydrogen energy Vol.41 No.4

<P>A series of mesoporous Cu-Ni-Al2O3-ZrO2 (XCNAZ) xerogel catalysts with different copper content (X, wt%) were prepared by a single-step epoxide-driven sol gel method, and they were applied to the hydrogen production by steam reforming of ethanol. All the calcined XCNAZ catalysts retained a mesoporous structure, and their surface area increased with increasing copper content. Metal-support interaction of XCNAZ catalysts decreased with increasing copper content due to the electronic effect. Nickel surface area and ethanol adsorption capacity of the catalysts exhibited volcano-shaped trends with respect to copper content. Among the catalysts, 0.2CNAZ catalyst exhibited the highest nickel surface area and the largest ethanol adsorption capacity. Catalytic performance in the steam reforming of ethanol over XCNAZ catalysts showed a volcano-shaped trend with respect to copper content. This result was well matched with the trend of nickel surface area. Thus, nickel surface area played a key role in determining the catalytic activity for steam reforming of ethanol. Among the catalysts tested, 0.2CNAZ catalyst with the highest nickel surface area (52.7 m(2)/g-Ni) showed the highest hydrogen yield (86.6%). That is, an optimal copper content was required for efficient hydrogen production by steam reforming of ethanol over XCNAZ catalysts. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.</P>

Effect of cathode geometry on the electrochemical performance of flat tubular segmented-in-series(SIS) solid oxide fuel cell

Mushtaq, U.,Kim, D.W.,Yun, U.J.,Lee, J.W.,Lee, S.B.,Park, S.J.,Song, R.H.,Kim, G.,Lim, T.H. Pergamon Press ; Elsevier Science Ltd 2015 International journal of hydrogen energy Vol.40 No.18

<P>A flat tubular segmented in series (SIS)-SOFC was fabricated with variable cathode thicknesses and the performance characteristics were analyzed. Vacuum slurry dip coating and screen printing technique were employed to coat the NiO-Ce(1)ScSZ(10) anode, Ce(1)ScSZ(10) electrolyte, and La0.6Sr0.4Co0.2Fe0.8 cathode on the extruded 3YSZ ceramic support. A sub module consisting of 5-cell with a total active electrode area of 4 cm(2) was interconnected in series using Ag-glass composite. Electrochemical performance analysis was conducted between 600 and 800 degrees C using 300 CC/min. 3 vol.% humidified hydrogen fuel and 1500 CC/mm air as oxidant. The results obtained from electrochemical impedance spectroscopy and current voltage polarization curves revealed a 57 mu m thick cathode layer as the optimum thickness. An application of LSCo as the cathode current collector on the surface of the cathode enhanced the performance by approximately 30% at 750 degrees C. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.</P>

Field-induced stretching and dynamic reorientation of functionalized multiwalled carbon nanotube aggregates in nematic liquid crystals

Tie, W.,Bhattacharyya, S.S.,Zhang, Y.,Zheng, Z.,Lee, T.H.,Lee, S.W.,Kim, T.H.,Lee, Y.H.,Lee, S.H. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.96 No.-

<P>Multiwalled carbon nanotubes (MWCNTs) exhibited distinct electrical stretching behavior in nematic liquid crystals (NLC) depending on nanotube surface state. We found that two different samples prepared by chemical functionalization (f-CNT) and physical grinding (g-CNT) revealed distinct field dependence from each other. The threshold stretching field was lower in the f-CNT aggregates than in g-CNT aggregates. This was attributed to polar functionality induced weakened van der Waals interaction in f-CNTs, which was confirmed in infrared (IR) and Raman spectroscopy. Dynamic reorientation of f-CNTs was observed under polarized optical microscopy where f-CNTs were found to follow orientation of NLC director. Uniformly aligned f-CNTs also exhibited selective light absorption in sufficiently long transient field off-state which could find potential applications in memory and modulator devices as well as the versatile functional composites. (C) 2015 Elsevier Ltd. All rights reserved.</P>