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Structure and Properties of AEMs

Finally, it should be emphasized that a good relative selectivity is a necessary, but not a sufficient property required for an optimal PEM or AEM in DAFC. There are multiple examples of membranes with very high p,. values, which exhibit very poor fuel cell performances. That means that the architecture of the three phases region is probably the bottleneck of the MEA performance and much attention should be paid to the properties of the ionomeric material use as a binder, forming nanometric structures whose properties could be rather different than those of the bulk materials [317]. Consequently, the properties of very thin films of ionomeric membranes on carbon and metal substrates should be studied for enhancing the performance of direct alcohol fuel cells. [Pg.205]

Changes to the fluorescence properties of a probe due to stacking effects can also be exploited in piezochromic macroscopic sensors. One such example is based on the liquid crystalline molecule cyano-substituted oligo(p-phenylene vinylene) (OPV), which forms columnar crystal stacks with pronounced n-n interactions, leading to excimer fluorescence [42]. In the solid state, the monomer emission is observed as a structured band in the green (2em = 481 nm). On exposure to external pressure, such as grinding with a pestle and mortar, the emission band is red-shifted (Aem = 548 nm) and the vibrational stracture is lost. The emission properties can be reversed upon heating the sample at 130 °C. The choice of... [Pg.424]

Morphological study for hybrid/composite manbranes is a very important method to investigate the microstructure and thus correlate with the properties of the composite polyelectrolytes. To better understand the structure-property relationship for PEMs, except for spectral analysis as mentioned earlier, microscopic studies such as field mission (FE) scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AEM) technologies are basically extensively utilized. [Pg.385]

Since many aliphatic PEMs were prepared from some new synthesized polymers in researches, nuclear magnetic resonance (NMR) is a useful tool to characterize the molecular structure of these polymers. In most cases, it was used to verify the coherence of the designed and actual structure of the new polymer [41,47]. Sometimes, it has also been used to identify a series of new polymers, when the researchers need to study on the effect of polymer structure on the properties of PEMs [65]. Confirmation of quaternization was also done by IH NMR spectroscopy (Figure 10.4), such as in cross-linked quaternized PVA (QPVA) [66] and cross-linked quaternized-CS [67] AEMs by observing the chemical shifts (ppm) of related functional groups (OH, CH, CH3) or increase in these peak intensities. [Pg.459]

In 2010, Hickner reported a series of AEMs prepared via the bromination, amination, quaternization, and alkalization of tetramethyl bisphenol A-based PSUs (Figure 11.4). The introduced benzylmethyl moieties could circumvent the polymer postmodiflcation by chloromethylation and control the ion content and distribution more quantitatively along the polymer backbone. Therefore, the ion conductivity and other properties of the AEMs could be tuned over a wide range, and structure-property relationship be clarified more clearly. ... [Pg.499]


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AEM

Structure and Properties of

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