1,721,018 research outputs found
Relative humidity influence on proton conduction of hydrated pellicular zirconium phosphate in hydrogen form☆
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Frequency response of polycrystalline samples of α−Zr(HPO4)2·H2O at different relative humidities☆
No full textSurvey on the Phase Transitions and Their Effect on the Ion-Exchange and on the Proton-Conduction Properties of a Flexible andRobust Zr Phosphonate Coordination Polymer
No full textThe flexible zirconium tetraphosphonate coordination
polymer with formula Zr(O3PCH2)2N-C6H10-N-
(O3CH2P)2X2−xH2+x·nH2O (X = H, Li, Na, K, 0 < x < 1, 4
< n < 7.5) (1) possesses an open framework structure with 1D
cavities decorated with polar and acids PO and POH
groups. 1 has been fully protonated by adding HCl and then
subjected to several acid−base ion-exchange reactions with
alkaline metals hydroxides. 1 is a very robust coordination
polymer because it can be regenerated in H- form using strong
acid solutions and ri-exchanged several times without
hydrolysis and loss of crystallinity. The flexibility of 1 has
been also studied by means of TDXD (temperature dependent X-ray diffraction) evidencing remarkable phase transformations
that lead to a different disposition of the water molecules. These transformations also influence the accessibility of the cations on
the P−OH groups placed inside the channels and thus the ion-exchange properties. The dependence of the proton conductivity
properties on these phase transitions has been also investigated and discussed
Composite membranes for fuel cells containing zirconium phosphate sulfophenylene phosphonates
No full textA critical investigation of the effect of hygrothermal cycling on hydration and in-plane/through-plane proton conductivity of Nafion 117 at medium temperature (70–130 °C)
No full textHydration, in-plane and through-plane conductivity of Nafion 117 membranes are investigated in the temperature range 70-130 degrees C and in the relative humidity (RH) range 50-90% upon cycling RH, at constant temperature, and cycling temperature at constant RH. Both temperature and RH cycling result in hysteresis of conductivity and hydration. During the RH cycle, conductivity changes at decreasing RH are faster than hydration changes, thus indicating the presence of water molecules contributing weakly to conductivity. During the temperature cycle, the in-plane conductivity shows a hysteresis loop where, as expected, the more hydrated state is the more conductive state as well. However, under the same conditions of temperature and RH, the through-plane conductivity exhibits an anomalous behaviour where the lower conductivity is associated with the higher hydration level. Upon temperature cycling, through-plane and in-plane conductivity show different temperature dependence during heating but the same dependence during cooling. This behaviour is attributed to irreversible structural changes occurring during heating when the membrane is pressed between the electrodes in the through-plane conductivity cell. The possible influence of the through-plane conductivity hysteresis on the performance of a PEM fuel cell in the range 70-130 degrees C is also discussed. (C) 2013 Elsevier B.V. All rights reserved
Composite membranes for fuel cells containing layered zirconium phosphate-sulfophenylene phosphonates
No full textShort side chain perfluorosulfonic acid membranes and their composites with nanosized zirconium phosphate: hydration, mechanical properties and proton conductivity
No full textAqueous dispersions of a short side chain perfluorosulfonic acid ionomer (equivalent weight 830 g eq.-1) and gels of nanosized zirconium phosphate (ZrP) in propanol are used for the preparation, by solution casting, of composite membranes with ZrP loading up to 13 wt%. These membranes, together with reference neat ionomer membranes, are characterized by mechanical stress-strain tests and in-plane conductivity determinations under different conditions of temperature and relative humidity (RH). The membrane hydration is also determined under the environmental conditions of mechanical and conductivity measurements. The conductivity of the neat ionomer membrane, at 90 and 120 °C, is weakly dependent on temperature but strongly influenced by changes in RH going from values around 0.02 S cm-1 at 25% RH to values around 0.25 S cm-1 at 90% RH. The conductivity of the composite membranes decreases with increasing filler content being however in the range of 0.01-0.02 S cm-1 at 25% RH and in the range of 0.16-0.23 S cm-1 at 90% RH at both temperatures. On the other hand the presence of the filler results in a significant increase in the Young's modulus (up to 80%) and in the yield stress (up to 124%) not only under ambient conditions but also at 80 °C and 80% RH
Proton conductivity of zirconium carboxy n-alkyl phosphonates with an α-layered structure
No full textIntercalation compounds of α-zirconium hydrogen phosphate with heterocyclic bases and their ac conductivity
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