Abstract
Membranes based on sulfonated synditoactic polystyrene (s-sPS) were thoroughly characterized by contrast variation small-angle neutron scattering (SANS) over a wide Q-range in dry and hydrated states. Following special sulfonation and treatment procedures, s-sPS is an attractive material for fuel cells and energy storage applications. The film samples were prepared by solid-state sulfonation, resulting in uniform sulfonation of only the amorphous phase while preserving the crystallinity of the membrane. Fullerenes, which improve the resistance to oxidation decomposition, were incorporated in the membranes. The fullerenes seem to be chiefly located in the amorphous regions of the samples, and do not influence the formation and evolution of the morphologies in the polymer films, as no significant differences were observed in the SANS patterns compared to the fullerenes-free s-sPS membranes, which were investigated in a previous study. The use of uniaxially deformed film samples, and neutron contrast variation allowed for the identification and characterization of different structural levels with sizes between nm and μm, which form and evolve in both the dry and hydrated states. The scattering length density of the crystalline regions was varied using the guest exchange procedure between different toluene isotopologues incorporated into the sPS lattice, while the variation of the scattering properties of the hydrated amorphous regions was achieved using different H2O/D2O mixtures. Due to the deformation of the films, the scattering characteristics of different structures can be distinguished on specific detection sectors and at different detection distances after the sample, depending on their size and orientation.
Highlights
Owing to their high conversion efficiency, high power density, low weight and volume, fast startup time, low operating temperature, and clean exhaust, polymer electrolyte membrane (PEM) fuel cells (PEMFC) are considered an attractive energy conversion technology for transportation applications, as demonstrated by the prototyped fuel cell vehicles and announced near future production plans by almost all major car manufacturers [1,2]
It has been demonstrated that the incorporation of CeO2 and amine-functionalized carbon nanotubes (ACNTs) into the Nafion matrix has a bifunctional consequence toward improving the proton transport due to acid–base interaction between the proton donor sulfonic group and proton acceptor amine group without the aid of water and the mitigating chemical degradation of membranes due to free radical reduction, which is promoted by the ceria [12]
The Fourier-transform infrared (FTIR) spectra of the films doped with C60 or C70 fullerenes are shown in Figure 2 in parallel to that from a δ-form sPS film
Summary
Owing to their high conversion efficiency, high power density, low weight and volume, fast startup time, low operating temperature (below 100 ◦ C), and clean exhaust, polymer electrolyte membrane (PEM) fuel cells (PEMFC) are considered an attractive energy conversion technology for transportation applications, as demonstrated by the prototyped fuel cell vehicles and announced near future production plans by almost all major car manufacturers [1,2]. The Nafion (Du PontTM ) is the most well-known material, and was established as benchmark for such applications [9] Despite their excellent properties, the PSFI materials present several drawbacks such as their high cost, lack of safety, and the requirement of supporting equipment during manufacturing and use [10]. They have limitations under operating conditions at high temperature (>80 ◦ C) and low relative humidity (RH), when a decrease in conductivity appears due to dehydration of the membrane at the anode side [11]. It has been demonstrated that the incorporation of CeO2 and amine-functionalized carbon nanotubes (ACNTs) into the Nafion matrix has a bifunctional consequence toward improving the proton transport due to acid–base interaction between the proton donor sulfonic group and proton acceptor amine group without the aid of water and the mitigating chemical degradation of membranes due to free radical reduction, which is promoted by the ceria [12]
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