15 research outputs found
Anhydrous Proton-Conducting Membrane Based on Poly-2-Vinylpyridinium Dihydrogenphosphate for Electrochemical Applications
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
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
Comparison of the off-resonance artifacts scores within four groups.
<p>Comparison of the off-resonance artifacts scores within four groups.</p
RF homogeneity data acquisition and image post-processing.
<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
Imaging parameters of the B-TFE sequence for short-axis ventricular cine.
<p>Notes: <i>TR</i> repetition time, <i>TE</i> echo time, <i>FA</i> flip angle.</p
Artifacts on the short-axis B-TFE images of four groups.
<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.
<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.
<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
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 polyÂ(tetrafluoroÂethylene)-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
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