High Temperature Energy Materials Research Center

KIST, South Korea

High Temperature Energy Materials Research Center

KIST, South Korea
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Seo J.-H.,Advanced Analysis Center | Seo J.-H.,Korea University | Park H.S.,Boston University | Yoo Y.,KAIST | And 5 more authors.
Nano Letters | Year: 2013

Researchers have recently discovered ultrastrong and ductile behavior of Au nanowires (NWs) through long-ranged coherent-twin-propagation. An elusive but fundamentally important question arises whether the size and surface effects impact the twin propagation behavior with a decreasing diameter. In this work, we demonstrate size-dependent strength behavior of ultrastrong and ductile metallic NWs. For Au, Pd, and AuPd NWs, high ductility of about 50% is observed through coherent twin propagation, which occurs by a concurrent reorientation of the bounding surfaces from {111} to {100}. Importantly, the ductility is not reduced with an increase in strength, while the twin propagation stress dramatically increases with decreasing NW diameter from 250 to 40 nm. Furthermore, we find that the power-law exponent describing the twin propagation stress is fundamentally different from the exponent describing the size-dependence of the yield strength. Specifically, the inverse diameter-dependence of the twin propagation stress is directly attributed to surface reorientation, which can be captured by a surface energy differential model. Our work further highlights the fundamental role that surface reorientations play in enhancing the size-dependent mechanical behavior and properties of metal NWs that imply the feasibility of high efficiency mechanical energy storage devices suggested before. © 2013 American Chemical Society.


Choi S.M.,High temperature Energy Materials Research Center | Choi S.M.,Korea University | Lee J.-H.,Korea University | Hong J.,High temperature Energy Materials Research Center | And 8 more authors.
Journal of Power Sources | Year: 2016

The chemical-diffusion and surface-exchange coefficients of a proton-conducting oxide, i.e., Ba(Zr0.84Y0.15Cu0.01)O3-δ upon a sudden change of water-vapor pressure at a fixed oxygen partial pressure are investigated via a conductivity relaxation technique. Conductivity relaxation during the hydration/dehydration process follows typical two-fold non-monotonic behavior that can be explained by decoupled chemical diffusion of H and O. However, the temperature dependence of the measured chemical-diffusion and surface-exchange coefficients is significantly different depending on the direction of the temperature change. In this study, we attempt to identify the origin of these unusual behaviors during the conductivity relaxation experiment via thorough microstructural and compositional analyses on sample surface. © 2016 Elsevier B.V. All rights reserved.


Choi S.M.,High Temperature Energy Materials Research Center | Choi S.M.,Korea University | Lee J.-H.,Korea University | Choi M.-B.,High Temperature Energy Materials Research Center | And 5 more authors.
Journal of the Electrochemical Society | Year: 2015

The total electrical conductivity of BaCeO3-based proton conductors with various dopants was measured using a DC-4 probe method. Yb and In were used as dopants to increase electrical conductivity and chemical stability, respectively. The electronic and ionic partial conductivities of samples of various compositions, i.e., BaCe1-x-yYbxInyO3-δ, where x = 0.1, y = 0.00, 0.05, and 0.10 (BC10Yb, BC10Yb05In, and BC10Yb10In, respectively) and x = 0.15, y = 0.00 (BC15Yb), were calculated based on the relevant defect chemistry model and interpreted as functions of fairly extensive ranges of P(O2) (-4 ≤ log P(O2) ≤ 0) and P(H2O) (-3.5 ≤log P(H2O)≤-1.5) at 700°C. The partial conductivities of all charge carriers, i.e., protons, holes, and oxygen vacancies, increased with Yb doping but decreased as In doping increased. The variations in the partial conductivity of holes and protons induced by the composition of doping constituents can be explained by the difference in electronegativity between dopant cations and oxygen anions as well as A- and B-site cations that are most critical in a general hopping conduction mechanism. Oxygen ion conductivity is controlled by the dopant size and content, which generally alter the lattice spacing and distortion of the perovskite structure. © 2015 The Electrochemical Society.


Lee J.-H.,High Temperature Energy Materials Research Center | Choi S.M.,High Temperature Energy Materials Research Center | Choi S.M.,Korea University | Lee J.-H.,Korea University | And 4 more authors.
International Journal of Hydrogen Energy | Year: 2014

The phase stability and electrical conductivity of a proton-conducting oxide, Ba(Zr0.84Y0.15Cu0.01)O 3-δ (BZYCu), sintered under various atmospheres was systematically investigated. The partial pressures of oxygen (PO2) and barium (PBa) were used as the tunable experimental parameters to control the surrounding atmosphere during sintering. According to the analysis, the potentially volatile species BaCO3, formed by the decomposition of BZYCu under a CO2-containing atmosphere at around 600 °C, was found to induce barium losses by evaporation. These barium losses, and the associated Y2O3 segregation, were the decisive factor in determining the phase stability and electrical conductivity of the resulting BZYCu; both of these properties deteriorated with barium evaporation. Maintaining the optimum balance of PO2 and PBa during sintering is crucial for minimizing Y2O3 segregation by kinetically suppressing the volatilization of barium. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Choi S.M.,High Temperature Energy Materials Research Center | Choi S.M.,Korea University | Lee J.-H.,Korea University | An H.,High Temperature Energy Materials Research Center | And 7 more authors.
International Journal of Hydrogen Energy | Year: 2014

We fabricated a uniquely designed anode-supported-type protonic ceramic fuel cell (PCFC) with a dual-electrolyte layer containing BaCe0.9Y0.1O3-δ (BCY) as the higher-proton-conducting phase and BaZr0.85Y0.15O3-δ (BZY) as the chemically stable protecting phase. In order to overcome the poor sinterability of the BZY electrolytes, which is a critical limitation in making thin and dense dual-electrolyte layers for anode-supported PCFCs, we employed aid-assisted enhanced sintering of BZY by adding 1 mol% of CuO. We also promoted the densification of the BZY layer by utilizing the higher sinterability of BCY that is attached to the top of the BZY layer. By properly adjusting the shrinkage behaviors of both the anode substrate and the dual-electrolyte layers, we were able to fabricate a fairly dense BZY/BCY dual-layer electrolyte with a thickness of less than 20 μm. In this paper, the novel strategies used to fabricate the PCFC based on dual-electrolyte layers are reported. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Ji H.-I.,High temperature Energy Materials Research Center | Hong J.,High temperature Energy Materials Research Center | Yoon K.J.,High temperature Energy Materials Research Center | Yoon K.J.,Korean University of Science and Technology | And 6 more authors.
Journal of Power Sources | Year: 2016

A more quantitatively controllable triple phase boundary (TPB) of a lanthanum strontium manganite/yttria-stabilized zirconia (LSM/YSZ) interface was constructed by using an YSZ ionic probe with well-defined dimensions. A bar-shaped, dense YSZ sintered body was employed as an ionic probe and embedded in the pellet-shaped, dense LSM bulk. The TPB length of the LSM/YSZ interface can be simply determined from the circumference of the YSZ bars. To identify the reaction mechanism of the oxygen reduction reaction (ORR) at the TPB of the LSM/YSZ interface, limited-contact AC impedance spectroscopy was used; this distinguished the LSM/YSZ interface related polarization from other polarizations present in the Pt/LSM/YSZ/Pt electrochemical cell. By analyzing the electrode-related polarizations in the electrochemical cell with the geometrically quantified YSZ ionic probe, the rate determining step of the ORR was the diffusion of adsorbed oxygen along the LSM bulk surface. In this paper, emphasis is placed on the experimental versatility and the limitations of our designed electrochemical analysis with bar-shaped ionic probes. © 2016 Elsevier B.V.


Jaiswal S.K.,High Temperature Energy Materials Research Center | Jaiswal S.K.,National Institute of Technology, Patna | Choi S.M.,High Temperature Energy Materials Research Center | Hong J.,High Temperature Energy Materials Research Center | And 5 more authors.
Ionics | Year: 2016

Proton-conducting ceramics have been very useful due to their potential applications in fuel cells, electrolysers, and hydrogen membranes. The proton-conducting fuel cell electrolytes (Ba1−xSrx)(Ce0.75Zr0.10Y0.15)O3−δ (x = 0–1.0) have been synthesized through sol-gel method and characterized with regard to phase, structural stability, and electrical conductivity. The structural behavior has been investigated by X-ray diffraction and theRaman spectroscopy. The XRD analysis shows perovskite-type cubic structure and values of lattice parameter lie in the range of ~4.29 to ~4.40 Å. Strontium substitution leads to lattice contraction, strengthening of the metal-oxygen bond, and increase of oxygen content (3−δ). The Raman spectra show different types of stretching/vibrations corresponding to octahedral, M-O stretching, and oxygen vacancies. The electrical conduction was found to be protonic in nature and decreases with increase of strontium insertion. The composition x = 0.4 shows relatively better structural stability against humid air/boiling water condition while inferior in carbon dioxide atmosphere. © 2016 Springer-Verlag Berlin Heidelberg


Kim S.-K.,High Temperature Energy Materials Research Center | Kwon E.-S.,High Temperature Energy Materials Research Center | Kwon E.-S.,Andong National University | Kim T.-H.,Andong National University | And 2 more authors.
Ceramics International | Year: 2014

The effects of atmospheric annealing on electrochemical performance for Nb2O5-doped Li4Ti5O12 anode materials have been investigated. The annealing of Nb2O 5-doped Li4Ti5O12 in Ar-gas suppressed the capacity fade, under the condition of a high charge-discharge rate, by virtue of an enhanced exchange reaction at the electrode/electrolyte interface. Under Ar-gas, Nb2O5-doped Li4Ti 5O12 was primarily reduced to increase the density of Ti3+ ions. This caused expansion of the Li4Ti 5O12 lattice, but had little impact on Li-ion diffusion into the lattice. When concurrent doping and annealing induced such compositional and electrical modification of Li4Ti5O 12, the polarization resistance of exchange reactions at the electrode/electrolyte interface decreased. Therefore, we have demonstrated that annealing in Ar-gas is capable of decreasing the resistance of exchange reactions at the electrode/electrolyte interface. © 2014 Elsevier Ltd and Techna Group S.r.l.


An H.,High Temperature Energy Materials Research Center | An H.,Hanyang University | Shin D.W.,Hanyang University | Choi S.M.,High Temperature Energy Materials Research Center | And 5 more authors.
ECS Transactions | Year: 2015

In this study, BaCe0.55Zr0.3Y0.15O3-δ was synthesized via solid state reaction (SSR) method and successfully sintered at relatively low temperature below 1400°C using various types of nickel oxide additives (simple oxide form, NiO and compound form, BaY2NiO5). In order to compare the effect of different forms of sintering additives, we investigated the electrical conductivity, chemical stability and sinterability via dilatometry, DC 4-probe conductivity measurement, XRD and TG analysis. In addition to the experimental results, possibility and limitation of compound form of sintering aid will also be addressed in this paper. © The Electrochemical Society.


Jaiswal S.K.,High Temperature Energy Materials Research Center | Jaiswal S.K.,National Institute of Technology, Patna | Choi S.M.,High Temperature Energy Materials Research Center | Yoon K.J.,High Temperature Energy Materials Research Center | And 4 more authors.
International Journal of Hydrogen Energy | Year: 2015

Deficiency in proton conducting perovskite-type oxides can be strongly influence the fuel cell properties. The effect of barium deficiency on the phase structure, cerium oxidation states, electrical conductivity and phase stability under carbon dioxide atmosphere of proton conducting oxides with composition of (Ba0.6-pSr0.4)(Ce0.75Zr0.10Y0.15)O3-δ (p - barium deficiency; 0.025 ≤ p ≤ 0.20) was systematically investigated. Rietveld refinement of the X-ray diffraction patterns shows the cubic structure in the space group Pm-3m up to p = 0.10. The lattice parameter decreases with 'p' and lie in the range ∼4.358 to ∼4.333 Å. XPS data show the percentage of Ce4+ increases which in turn, reduces the oxygen non-stoichiometry (δ) - values with deficiency (p). Raman spectra show the presence of oxygen vacancies which decreases with 'p'. The conduction behavior depicts the protonic nature with activation energy lying in the range of 0.24-0.29 eV. The stability of deficient compositions (0.025 ≤ p ≤ 0.20) enhances in carbon dioxide (CO2) atmosphere in compare to p = 0. © 2015 Hydrogen Energy Publications, LLC.

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