Occurrence and mobility of major and trace elements in groundwater from pristine volcanic aquifers in Jeju Island, Korea

Koh, D.C.,Chae, G.T.,Ryu, J.S.,Lee, S.G.,Ko, K.S. Pergamon Press ; Elsevier Science Ltd 2016 Applied geochemistry Vol.65 No.-

<P>Major and trace elements in groundwater from basaltic aquifers in pristine conditions were investigated in a volcanic island to evaluate sources, sinks, and mobility of elements over a wide range of mineralization conditions with total dissolved solids from 50 mg/L to 3400 mg/L. Groundwater was highly undersaturated with respect to primary silicate minerals, indicating that dissolution of basaltic rocks may continue under conditions with precipitation of calcite and secondary silicates. Evolution of B/Cl ratio in groundwater from marine aerosols to basaltic rocks showed that the ratio could be used as a conservative tracer for interactions between water and basaltic rocks. Relative mobility (RM) of elements calculated using the concentrations of elements in the local basaltic rocks and those in groundwater showed that mobility decreased in the order of B > Rb > Na > K > Mg > Ca > Mo > V > Si > Sr > Sc > P > U > Zn > Pb > Cr > Cu > Ba > Ni > Ti > (Mn, Al, Fe, Co, Th) indicating that oxyanion-forming elements and alkali metals had the highest mobility. Compared to average RM, V had decreased mobility, and Fe and Mn had increased mobility in anoxic groundwater while V, Mo, and U had higher mobility in oxic-alkaline water. The sources of V, Cr, Cu, and Zn in rocks were estimated using the partition coefficients between minerals and basaltic melt, and the disparity between sources and mobility indicated that sinks are more important for controlling the concentrations of these elements in groundwater than the contents in the rocks. Principal component analysis (PCA) of hydrogeochemical parameters in groundwater produced three principal components (PC) which represent dissolution of basaltic rocks without significant attenuation of released solutes, higher degree of water-rock interactions resulting in oxic-alkaline conditions, and attenuation of Zn and Cu in higher pH, respectively. Spatial distribution of PCs revealed that groundwater with elevated concentrations of mobile elements was concentrated in the southwestern area and that concentrations of V and Cr were more scattered, which is likely to be controlled by pH and redox states of groundwater as well as degree of water-rock interactions. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Ultrahigh electrically and thermally conductive self-aligned graphene/polymer composites using large-area reduced graphene oxides

Kumar, P.,Yu, S.,Shahzad, F.,Hong, S.M.,Kim, Y.H.,Koo, C.M. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.101 No.-

<P>In this work, for the first time we fabricated highly self-aligned large-area reduced graphene oxide/poly (vinylidene fluoride-co-hexafluoropropylene) (rLGO/PVDF-HFP) composite films through simple solution casting followed by low temperature chemical reduction process. The resulting free-standing rLGO/PVDF-HFP composite thin film revealed excellent electrical conductivity of similar to 3000 S/m and ultrahigh inplane thermal conductivity of similar to 19.5 W/mK at rLGO content of 27.2 wt %. This ultrahigh electrical and thermal conductivity were attributed to the good interfacial interaction, effective chemical reduction, high aspect ratio, and preferential orientation of graphene sheets along the film direction. We believe that our new fabrication procedure can be effectively used for large-scale production and commercialization of conductive composite materials for many thermal and electrical conduction applications. (C) 2016 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>

Electrical properties of transferred graphene films on pre-treated polyimide substrate by inductively coupled plasma

Kim, J.K.,Kang, K.H.,Lee, J.M. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.109 No.-

<P>In this study, the effects of the pre-treatment of PI films using inductive coupled plasma, according to the gas species, on the electrical properties of a graphene/PI substrate system were investigated. The surface treatment of PI films using inductively coupled O-2, Ar, CH4, and CHF3 plasma was performed. It was found that surface morphology and hydrophobicity are critically important substrate conditions that determine the improvement of the electrical properties of graphene transferred onto the plasma-treated PI substrate. Compared to the electrical properties of untreated PI, the CH4 and CHF3 plasma treated samples showed enhanced electrical conductivity of the graphene devices. However, the electrical conductivities of the PI treated by Ar and O-2 plasma were degraded. CHF3 plasma treatment leads to the sheet resistance of 528 Omega/sq, which is the best result in this experiment. The enhanced electrical properties of the graphene on CHF3- and CH4-treated PI film was attributed to the reduced roughness and the removal of C-O and O-H chemical species by hydrophobization of the PI substrate. The fluorine groups led to a decrease of the surface free energy of the PI films, which resulted in the lowest sheet resistance. (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>

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>