Anion-exchange
membrane (AEM) degradation during fuel cell operation
represents the main challenge that hampers the implementation of AEM
fuel cells (AEMFCs). Reported degradation values of AEMs are difficult
to reproduce as no standard methods are used. The present use of different
techniques based on exposure of membranes to aqueous KOH solutions
under different conditions and measuring different outputs during
time does not allow for a reliable and meaningful comparison of reported
degradation data of different AEMs. In this study, we present a practical
and reproducible
ex-situ
technique to measure AEM
degradation in conditions that mimic an
operando
fuel
cell environment. In this novel technique, we measure the change of
the true hydroxide conductivity of the AEM over time, while exposing
it to different relative humidity conditions. The technique does not
make use of liquid alkaline solution, thus simulating real fuel cell
conditions and providing a good baseline for comparative degradation
studies.
Water
content plays a major role in the properties of anion-exchange
membranes (AEMs) and, therefore, in the AEM fuel cell (AEMFC) performance
and performance stability. Characterization of AEMs during membrane
degradation is critical in order to understand the membrane behavior
during fuel cell operation time. In spite of its importance, the relationship
between different membrane properties during chemical degradation
has yet to be investigated. In this study, we measure the changes
in AEM propertiesin particular, ion exchange capacity (IEC),
water uptake (WU) and conductivityduring membrane chemical
degradation in alkaline medium. To the best of our knowledge, this
is the first time this kind of data has been investigated. While all
the properties change during AEM degradation, results indicate that
membrane WU decreases linearly with decreasing IEC; however, AEM ion-conductivity
shows a sigmoidal-like shape relationship with IEC. We introduce a
simple model to explain these effects.
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