1,721,019 research outputs found
A 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
Survey 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
Short 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
Layered zirconium alkylphosphates: Suitable materials for novel PFSA composite membranes with improved proton conductivity and mechanical stability
No full textNanosized α-layered monohydrogen zirconium phosphate (ZP) has been organically modified by reacting the monohydrogen phosphate groups with of 1,2 epoxydodecane solutions in tetrahydrofuran. The materials thus obtained (ZP(C12)x, with x in the range 0.74-2.1) have been characterized by TEM, thermogravimetric analysis, X-ray powder diffraction and solid state 13C CPMAS NMR. The functionalization leads to a disordered layer packing without substantial alteration of the inorganic framework of the α-layer of pristine ZP. Samples with x=0.74 and 1.15 have been used as fillers of membranes based on a recast short side chain perfluorinated ionomer with EW=830. Composite membranes with 5-15wt% filler loadings have been characterized by stress-strain mechanical tests, proton conductivity measurements and water uptake determinations under controlled conditions of temperature and relative humidity (RH). The presence of the filler results in a significant increase in the Young[U+05F3]s modulus of the neat ionomer up to a maximum of 55% and 67% at room temperature and at 80°C/70% RH, respectively. At 100°C and in the RH range 50-90%, the conductivity of the composite membranes is higher than that of the neat ionomer, and the proportional increase in conductivity (+72% for RH=50% and +32% for RH=90%) is maximum for 10wt% filler loading. Surprisingly, under the same conditions of temperature and RH, the hydration of the most conductive composite membrane is lower than the hydration of the neat ionomer
Starch/zirconium phosphate composite films: Hydration, thermal stability, and mechanical properties
No full textComposite films of plasticized potato starch filled with 1, 4, and 6 wt% zirconium phosphate (ZrP) particles have been prepared by casting mixtures of gelatinized starch, a gel of partially exfoliated ZrP in water, and glycerol. The XRD patterns of the composite films reveal the formation of glycerol intercalated ZrP for the highest filler loadings (4 and 6 wt%) while suggest partial filler exfoliation for the composite with 1 wt% ZrP, in agreement with TEM analysis. The presence of the filler improves the thermal resistance of the starch, both at low and, particularly, at high temperature. The composites also exhibit a significant enhancement in the Young's modulus (from ∼700 MPa for neat starch up to ∼1600 MPa for 6 wt% filler loading) and in the yield stress (from ∼17 to ∼38 MPa). The increase in stiffness is concomitant with a water uptake reduction, which is maximum at 100% relative humidity
Aminoalcohol functionalized zirconium phosphate as versatile filler for starch-based composite membranes
No full textMicrocrystalline zirconium phosphate was exfoliated by treatment with aqueous solutions of α,ω-alkylaminoalcohols and employed for the fabrication of potato starch composite membranes. Glycerol-based and glycerol-free composite membranes, containing 5 wt% of filler, were prepared from gelatinized starch and characterized for their physico-chemical properties. Despite of a partial filler reaggregation, as revealed by XRD and SEM analysis, all the composites exhibited a significant increase in the Young's modulus with respect to the glycerol-starch membrane, up to 80% and 190% for the glycerolbased and the glycerol-free composites, respectively. For both kinds of membranes the filler delays to a large extent the starch decomposition above about 300 °C. A significant reduction in the water uptake of the composites was also observed with respect to the neat glycerol-based membrane, up to about 70% for the glycerol-free composites
Nafion - zirconium phosphate nanocomposite membranes with high filler loadings: conductivity and mechanical properties
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