Ionomers for proton exchange membrane fuel cells with sulfonic acid groups on the end‐groups: Novel branched poly(ether‐ketone)s with 3,6‐ditrityl‐9H‐carbazole end‐groups

Abstract

Branched wholly aromatic poly(ether‐ketone)s (PEKs) bearing clusters of sulfonic acid groups on a novel end‐group, 3,6‐ditrityl‐9H‐carbazole, were synthesized by the polycondensation of activated aromatic difluorides and 4,4′‐dihydroxybenzophenone in the presence of the above end‐group and trifunctional branching agent, 1,3,5‐tris(4‐(4‐fluorophenylsulfonyl)phenyl)benzene, followed by postsulfonation to introduce up to 8 sulfonic acid groups on each endgroup in PEKs. PEMs of these sulfonated branched PEKs with the same level of IECs (0.99–1.25 mequiv./g) as Nafion® (0.91 mequiv./g) showed proton conductivities (66–95 mS/cm) comparable to that (98 mS/cm) of Nafion®®. TEM analysis showed significantly phaseseparated, and worm‐like, highly connected morphology in the PEK membranes.

Ion Transport by Nanochannels in Ion-Containing Aromatic Copolymers

“…Significantly phaseseparated, highly interconnected, and wormlike morphologies (nanochannels) with a size of 2−3 nm were observed by TEM. 79 The high ion channel connectivity could be the principal reason for the relatively high conductivities comparable to Nafion, at IEC values similar to Nafion.…”

Structure‐Morphology‐Property Relationships of Non‐Perfluorinated Proton‐Conducting Membranes

“…A similar system but where the chains are terminated with carbazole-based functionalities also exhibits a worm-like, highly connected morphology and high levels of proton conductivity. [ 50 ] …”

Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs)

“…These designs included linear [136], branched [137,138], and dendritic multiblock [139,140] structures. Since the authors used the post-polymerization sulfonation method, electron-withdrawing groups, such as ketone and/or sulfone groups, were introduced onto the PEM backbone to avoid main chain sulfonation and enhance the solubility of the resulting polymers.…”

“…For the former strategy, sulfonated branched PEKs were synthesized in accordance with the concept of PEMs with sulfonatable end groups, as shown in Fig. 35(b) [137,138]. Hexaphenylbenzene moieties and 3,6-ditrityl-9H-carbazole moieties were used as end groups for sulfonation, where six and eight sulfonic acid groups, respectively, were successfully introduced.…”