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991.
Seo SJ Woo JJ Yun SH Lee HJ Park JS Xu T Yang TH Lee J Moon SH 《Physical chemistry chemical physics : PCCP》2010,12(46):15291-15300
Interfacial resistances between the polymer electrolyte membrane (PEM) and catalyst layer (CL) in membrane-electrode assemblies (MEAs) have yet to be systematically examined in spite of its great importance on the fuel cell performance. In order to investigate ionic transport through the PEM/CL interface, the symmetrical impedance mode (SIM) was employed in which the same type of gas was injected (H(2)/H(2)). In this study, the ionic transport resistance at the interface was controlled by the additionally sprayed outer ionomer on the surface of each CL. Effectiveness of the outer ionomer on ionic transport at the interface was quantitatively explained by the reduced contact, proton hydration, and charge transport resistances in the SIM. To characterize the ionic transport resistance, the concept of total resistance (R(tot)) in the SIM was introduced, representing the overall ohmic loss due to proton transport in an MEA. This concept was successfully supported via an agreement of the interpretation and the linear correlation that was obtained between the admittance (1/R(tot)) and the performance of a fuel cell in the ohmic loss region. This correlation will enable researchers to predict the performance of a fuel cell under the influence of proton transport by examining the R(tot) in the SIM. 相似文献
992.
Thermoelectric properties of nanocomposite thin films prepared with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) and graphene 总被引:1,自引:0,他引:1
Carbon nanotubes (CNTs), either single wall carbon nanotubes (SWNTs) or multiwall carbon nanotubes (MWNTs), can improve the thermoelectric properties of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT?:?PSS), but it requires addition of 30-40 wt% CNTs. We report that the figure of merit (ZT) value of PEDOT?:?PSS thin film for thermoelectric property is increased about 10 times by incorporating 2 wt% of graphene. PEDOT?:?PSS thin films containing 1, 2, 3 wt% graphene are prepared by solution spin coating method. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses identified the strong π-π interactions which facilitated the dispersion between graphene and PEDOT?:?PSS. The uniformly distributed graphene increased the interfacial area by 2-10 times as compared with CNT based on the same weight. The power factor and ZT value of PEDOT?:?PSS thin film containing 2 wt% graphene was 11.09 μW mK(-2) and 2.1 × 10(-2), respectively. This enhancement arises from the facilitated carrier transfer between PEDOT?:?PSS and graphene as well as the high electron mobility of graphene (200,000 cm(2) V(-1) s(-1)). Furthermore the porous structure of the thin film decreases the thermal conductivity resulting in a high ZT value, which is higher by 20% than that for a PEDOT?:?PSS thin film containing 35 wt% SWNTs. 相似文献
993.
Lee R Kim J Kim SY Jang SM Lee SM Choi IH Park SW Shin JS Yoo KH 《Lab on a chip》2012,12(13):2377-2384
Label-free cell-based assays have emerged as a promising means for high-throughput screening. Most label-free sensors are based on impedance measurements that reflect the passive electrical properties of cells. Here we introduce a capacitance-based assay that measures the dielectric constant (capacitance) of biological cells, and demonstrate the feasibility of analyzing endocytosis and screening chemotherapeutic agents with this assay. Endocytosis induces a change in the zeta potential, leading to a change in the dielectric constant which enables real-time endocytosis monitoring using the capacitance sensor. Additionally, since the dielectric constant is proportional to cell radius and cell volume, cell viability can be estimated from the change in capacitance. Therefore, the capacitance sensor array can also be used for cytotoxicity testing for large-scale chemotherapeutic screening. 相似文献
994.
Two new isostructural mixed metal selenites, PbMSeO(6) (M = Mo(6+) or W(6+)), that are only composed of second-order Jahn-Teller (SOJT) distortive cations have been synthesized by standard solid-state reaction techniques using PbO, SeO(2), and MoO(3) (or WO(3)) as reagents. The structures of the reported materials were determined by single-crystal and powder X-ray diffraction. The materials show a three-dimensional framework structure consisting of chains of corner-shared MO(6) octahedra connected by SeO(3) and PbO(8) polyhedra. All of the constituent cations (M(6+), Se(4+), and Pb(2+)) are in distorted environments attributable to second-order Jahn-Teller (SOJT) effects. While the Mo(6+) cations undergo a C(2)-type intraoctahedral distortion toward an edge, the Se(4+) and Pb(2+) cations are in asymmetric coordination environments attributable to their lone pairs. The SeO(3) polyhedra strongly influence the direction of the Mo(6+) intraoctahedral distortion. Infrared spectroscopy, thermogravimetric analysis, the magnitudes of out-of-center distortions, and dipole moment calculations are also presented. Crystal data: PbMoSeO(6), triclinic, space group P-1 (No. 2), with a = 6.8944(6) ?, b = 7.2219(6) ?, c = 10.8294(9) ?, α = 99.751(2)°, β = 99.996(2)°, γ = 90.041(2)°, V = 523.09(8) ?(3), and Z = 2; PbWSeO(6), triclinic, space group P-1 (No. 2), with a = 6.8689(2) ?, b = 7.2398(2) ?, c = 10.9037(3) ?, α = 99.699(4)°, β = 100.348(3)°, γ = 90.139(4)°, V = 525.50(3) ?(3), and Z = 2. 相似文献
995.
KS Lim DW Ryu WR Lee EK Koh HC Kim CS Hong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(37):11541-11544
Crystal clear: An end-on (EO) azide-bridged Co(II) layer (see scheme; 1) with coordinated water molecules, long spacer p-XBP4 ligands, and unbound azide anions was evacuated to generate a dehydrated sample of 2. A reversible crystal-to-amorphous structural transformation accompanied by color and magnetic changes takes place between 1 and 2 by using a desolvation-solvation protocol. 相似文献
996.
Lee YR Kim IY Kim TW Lee JM Hwang SJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(8):2263-2271
Homogeneously mixed colloidal suspensions of reduced graphene oxide, or RGO, and layered manganate nanosheets have been synthesized by a simple addition of the exfoliated colloid of RGO into that of layered MnO(2). The obtained mixed colloidal suspensions with the RGO/MnO(2) ratio of ≤0.3 show good colloidal stability without any phase separation and a negatively charged state with a zeta (ζ) potential of -30 to -40?mV. The flocculation of these mixed colloidal suspensions with lithium cations yields porous nanocomposites of Li/RGO-layered MnO(2) with high electrochemical activity and a markedly expanded surface area of around 70-100?m(2) g(-1). Relative to the Li/RGO and Li/layered MnO(2) nanocomposites (≈116 and ≈167?F?g(-1)), the obtained Li/RGO-layered MnO(2) nanocomposites deliver a larger capacitance of approximately 210?F?g(-1) with good cyclability of around 95-97?% up to the 1000th cycle, thus indicating the positive effect of hybridization on the electrode performances of RGO and lithium manganate. Also, an electrophoretic deposition of the mixed colloidal suspensions makes it possible to easily fabricate uniform hybrid films composed of graphene and manganese oxide. The obtained films show a distinct electrochemical activity and a homogeneous distribution of RGO and MnO(2). The present experimental findings clearly demonstrate that the utilization of the mixed colloidal suspensions as precursors provides a facile and universal methodology to synthesize various types of graphene/metal oxide hybrid materials. 相似文献
997.
998.
The effect of longitudinal optical phonon field on the ground state and low lying-excited state energies of a hydrogenic impurity in a Zn1−xCdxSe/ZnSe strained quantum dot is investigated for various Cd content using the Aldrich-Bajaj effective potential. We consider the strain effect considering the internal electric field induced by the spontaneous and piezoelectric polarizations. Calculations have been performed using Bessel function as an orthonormal basis for different confinement potentials of barrier height. Polaron induced photoionization cross section of the hydrogenic impurity in the quantum dot is investigated. We study the oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of incident photon energy for 1s-1p and 1p-1d transitions with and without the polaronic effect. It is observed that the potential taking into account the effects of phonon makes the binding energies more than the obtained results using a Coulomb potential screened by a static dielectric constant and the optical properties of hydrogenic impurity in a quantum dot are strongly affected by the confining potential and the radii. It is also observed that the magnitude of the absorption coefficients increases for the transitions between higher levels with the inclusion of phonon effect. 相似文献
999.
1000.
Byung Sun Park Sang Woo Lee In Tae Kim Jin Sung Tae So Ha Lee 《Heteroatom Chemistry》2012,23(1):66-73
A series of new ceramidine derivatives 8a–f has been synthesized in 4–5 steps involving a Wittig reaction of ceramidonine with various triphenylphosphonium bromides. Their UV and photoluminescence (PL) properties are reported. The compounds showed medium to strong PL between 502 and 522 nm at a concentration of 1 × 10−5 M CH2Cl2. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:66–73, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20753 相似文献