15 research outputs found

    Anhydrous Proton-Conducting Membrane Based on Poly-2-Vinylpyridinium Dihydrogenphosphate for Electrochemical Applications

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    Anhydrous electrolytes with high proton conductivity and adequate chemical stability in the temperature range of 120–180 °C can be very useful in electrochemical devices such as fuel cells, sensors, and electrolyzers. Developing such proton-conducting materials has been challenging. We have fabricated and characterized the performance of such membranes, based on poly-2-vinylpyridinium dihydrogenphosphate (P2VP-DHP), that can operate in the range of 105–180 °C under anhydrous conditions. The ionic conductivity of the membrane was 0.01 S cm<sup>–1</sup> at 140 °C. Proton conduction occurs by ionization of the quaternary ammonium group and by Grotthus-type transport that involves the rapid rotation of the dihydrogenphosphate anion. The activation energy for proton transport was 50 kJ/mol. The transport number of the proton was measured by impedance spectroscopy and potential-step techniques. The measured value was in the range of 0.17–0.20. A membrane-and-electrode assembly using the P2VP-DHP was tested as an electrochemical hydrogen pump. This demonstration shows the advantage of membranes based on a polymer amine salt in electrochemical applications that require operating under water-free conditions. Weight loss measurements at 120 °C in air confirmed the thermal and oxidative stability of the membrane. The properties of the P2VP-DHP membrane reported here provide the basis for further development of proton-conducting polymer electrolyte membranes for operating temperatures above 100 °C in anhydrous environments

    Near-Infrared Emission and Photon Energy Upconversion of Two-Dimensional Copper Silicates

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    BaCuSi<sub>4</sub>O<sub>10</sub> (Han blue), CaCuSi<sub>4</sub>O<sub>10</sub> (Egyptian blue), and SrCuSi<sub>4</sub>O<sub>10</sub> are pigments found in many ancient artifacts all over the world. Behind their brilliant color, we demonstrate here that these ancient pigments are strong candidates for photonic materials due to their bright Stokes and anti-Stokes emissions. These pigments give near-infrared emissions (NIR) from Cu<sup>2+</sup> centered at around 930 nm under excitation of 440–800 nm light. This NIR emission can also be produced by pumping using a NIR laser diode. With the rise of pumping density, the emission bandwidth increases notably and stretches to the visible region, giving rise to bright and broadband photon upconversion (UC). This photon UC process is interpreted in terms of laser-driven blackbody radiation from the ancient pigments

    RF homogeneity data acquisition and image post-processing.

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    <p>Short axis cardiac modulus images (a, d) and B1 maps (b, e) acquired with single-source (a, b) and dual-source (d, e) RF excitation. The ROIs outlining the heart were placed on the modulus images (a, d), and then the same ROIs were copied to B1 maps (b, e) to evaluate the B1 homogeneity. Improved B1 homogeneity and reduced areas of dark spots were seen on (e) compared with (b). The distribution of the mean percentage of the achieved FA calculated from all pixels inside the ROI of the B1 maps was shown on figure c (without) and f (with dual-source RF excitation). The distribution of FA on (f) was more concentrated and uniform than that on (c). In addition, the average percentage of achieved FA on (f) was higher than that on (c).</p

    Artifacts on the short-axis B-TFE images of four groups.

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    <p>The cine images acquired in groups M0 (a), M1 (b) and M2 (c) were all suffered from dark banding artifacts (thin arrows) seriously. Compared with group M0 (a), group M1 (b) reduced the dark banding artifacts to some extent and was better on the image homogeneity. Within the four groups, the CR of group M2 (c) was largest when the FA was increased, however, the off-resonance artifacts of group M2 (c) was pronounced in the ventricular wall (thin arrows). The off-resonance artifacts (thin arrows) of group M3 (d) were reduced and shifted away from the heart with dual-source RF shimming and a shortest TR, furthermore, group M3 (d) achieved good CR of blood-to myocardium contrast.</p

    Image contrast at B-TFE cine imaging.

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    <p>Bar graphs showed CRs at LV-to-septum contrast (a) and RV-to-septum contrast (b) imaging with and without dual-source RF shimming. For CRs, the images with use of dual-source RF shimming (M1, M2, M3) revealed greater LV-to-septum and RV-to-septum versus the corresponding images with single-source mode. The CR of M2 was the largest with the FA = 58°. *** P<0.001 vs. single-source mode.</p

    Comparison of the LV(RV)-to-septum contrast within the four groups.

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    <p>Notes: The <i>P</i> value was comparison between group M0 and groups M1, M2, M3, separately.</p

    Improved Thermal Stability of Ferroelectric Phase in Epitaxially Grown P(VDF-TrFE) Thin Films

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    In recent years ferroelectric polymers have attracted much attention due to their potentials in flexible electronics. To satisfy the requirements of low operation voltage and low power consumption, it is required to reduce the ferroelectric film thickness down to, for example, 100 nm. However, decreased film thickness results in low crystallinity and thus worse electrical performance. One possible solution is to realize the epitaxial growth of ferroelectric thin films via effective control of structure and orientation of ferroelectric crystals. Here we report our work on poly­(tetrafluoro­ethylene)-template-induced ordered growth of ferroelectric thin films. We focus on the study of thermal stability of ferroelectric phase in these ferroelectric films. Our work indicates that epitaxial growth effectively increases the crystallinity and the melting and ferroelectric phase transition temperatures and implies the extended application of ferroelectric devices at higher temperature

    Luffa-Sponge-Like Glass–TiO<sub>2</sub> Composite Fibers as Efficient Photocatalysts for Environmental Remediation

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    Structural design of photocatalysts is of great technological importance for practical applications. A rational design of architecture can not only promote the synthetic performance of photocatalysts but also bring convenience in their application procedure. Nanofibers have been established as one of the most ideal architectures of photocatalysts. However, simultaneous optimization of the photocatalytic efficiency, mechanical strength, and thermal/chemical tolerance of nanofibrous photocatalysts remains a big challenge. Here, we demonstrate a novel design of TiO<sub>2</sub>–SiO<sub>2</sub> composite fiber as an efficient photocatalyst with excellent synthetic performance. Core–shell mesoporous SiO<sub>2</sub> fiber with high flexibility was employed as the backbone for supporting ultrasmall TiO<sub>2</sub> nanowhiskers of the anatase phase, constructing core@double-shell fiber with luffa-sponge-like appearance. Benefitting from their continuously long fibrous morphology, highly porous structure, and completely inorganic nature, the TiO<sub>2</sub>–SiO<sub>2</sub> composite fibers simultaneously possess high photocatalytic reactivity, good flexibility, and excellent thermal and chemical stability. This novel architecture of TiO<sub>2</sub>–SiO<sub>2</sub> glass composite fiber may find extensive use in the environment remediation applications
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