Nanostructure and properties of proton‐conducting sulfonated poly(ether ether ketone) (SPEEK) and zirconia–SPEEK hybrid membranes for direct alcohol fuel cells: effect of the nature of swelling solvent and incorporation of heteropolyacid

Abstract

The influence, on membrane nanostructure and properties, of water or ethanol as swelling solvent of sulfonated poly(ether ether ketone) (SPEEK) and zirconia-SPEEK hybrid membranes prepared using the sol-gel process has been investigated. Independent of the solvent, small-angle X-ray scattering measurements reveal the existence of a two-level hierarchical structure in SPEEK of greater sulfonation level, consisting of solvent-swelled spatially correlated primary SO 3 H-rich ionic clusters of around 15 Å in size, forming larger secondary aggregates well dispersed in the PEEK matrix. The size of the primary nanodomains and the connectivity between domains are determining parameters for protonic conductivity, solvent swelling ability and permeability of the membranes. For both SPEEK and zirconia-SPEEK membranes containing ethanol, the pronounced affinity of ethanol molecules with SPEEK leads to an increase in the size of ionic clusters and of the number of connecting channels between clusters compared to membranes containing water. This promotes solvent swelling and proton conductivity. The increase in permeability to water induced by incorporation of ethanol in place of water in both polymeric and hybrid membranes is less in the hybrid membranes. This result suggests that the potential use of zirconia-SPEEK hybrid membranes in direct alcohol fuel cells is more promising than that of pure SPEEK, due not only to the less probable alcohol and water penetration in the membranes associated with their lower permeability, but also to the fact that an eventual penetration of alcohol in hybrid membranes should reduce the risk of cathode flooding compared to zirconia-free SPEEK membranes.

Sulfonated Aromatic Polymers and Organically Modified Montmorillonite Nanocomposite Membranes for Fuel Cells Applications

“…These ionic sites, due to their hydrophilicity, tend to phase separate from hydrophobic back bones of the polymer chains and form interconnected 3D nanochannel networks, rich of hydrophilic functional domains, which are responsible for proton conduction. [26] Kawaguti et al [27] studied these nanochannels in SPEEK. They proved that with an increase in the DS, the proton conducting nanochannels were formed more interconnected, which causes an increase in the proton conductivity.…”

“…The microstructure of the hydrophilic nanochannels in hydrated sulfonated aromatic polymers can be described as being narrower, more branched and less interconnected in comparison with annealed Nafion. [27] Figure 2 shows the microstructure of SPEEK, SPPO, and SPES schematically.…”

Polyelectrolyte microcapsules as ionic liquid reservoirs within ionomer membrane to confer high anhydrous proton conductivity

“…Fig. 6 revealed that all the membranes exhibited a broad crystalline band at 2q ¼ 9e21 , corresponding to the ordered stacking of hydrophobic backbones [39]. Compared with SPEEK control membrane, SP-PMC-6% (Fig.…”

Enhanced anhydrous proton conductivity of polymer electrolyte membrane enabled by facile ionic liquid-based hoping pathways

“…Accordingly, SAXS was utilized to further probe the structure of the membrane and the results were shown in Fig. Fig.3b revealed that all the membranes exhibited a broad crystalline band at 2θ=12-25°, corresponding to the ordered stacking of hydrophobic backbone [43]. It could be found that typical scattering peaks at the q values ranging of 0.50-0.56 nm -1 were observed for all the membranes, inferring the existence of nanophase separation and ionic cluster [41].…”