Polymer Electrolyte Membranes Based on Multiblock Poly(phenylene ether ketone)s with Pendant Alkylsulfonic Acids: Effects on the Isomeric Configuration and Ion Transport Mechanism

Abstract

Two structural variations of multi-block poly(phenylene ether ketone)s (bSPPEKs) with pendant alkylsulfonic acids were prepared by a polycondensation reaction between oligomeric difluoroand diphenoxide-precursors, followed by successive demethylation and sulfonation processes.Two isomers, bis[4-fluoro-3-(4'-methoxylbenzoyl)]biphenyl (p-BFMBP) and bis[5-fluoro-2-(4'-methoxylbenzoyl)]biphenyl (m-BFMBP), were prepared as the difluoro-starting monomers. The corresponding polymer membranes were obtained with good mechanical stability to facilitate the further characterizations. The morphology of bSPPEKs was confirmed by atomic force microscopy (AFM), from which the distinct phase separation could be identified with the average hydrophilic domain size of ca. 15-20 nm for the m-bSPPEKs. It is worth noting that both m-and p-bSPPEKs show quite comparable, or even better, ion conduction capacities than commercially available Nafion membrane, especially under low relative humidity conditions (30-50%), suggesting their promising future as polymer electrolyte membrane candidates.Meanwhile, the proton conductivities of all the m-bSPPEKs were found to be greater than those of the p-bSPPEKs over the entire relative humidity range, indicating better water-retention capacity and lower resistance to the ion transport. In addition, molecular dynamics simulation (MDS) was employed to extensively explore the structure-property relationship between the two polymers. The length, angle and torsion distribution results clearly reveal their steric configurations, i.e., a longer length and smaller angle in the side chain, together with a smaller torsion angle in the main chain for m-bSPPEKs, which produces slightly more free volume inside the polymer matrix. Analysis of the diffusion coefficients and coordination numbers shows that there is more water clustering around the sulfonic acid groups in the meta-polymers, than in the para-polymers.

Multiblock poly(Phenylene ether nitrile)s with pendant sulfoalkoxyl side chain for H2/air fuel cells at low humidity condition

“…Proton exchange membranes (PEMs) are one of the key materials used in these fuel cells, and various types of PEM membranes have been developed. Among these, perfluorosulfonic acid (PFSA) membranes, such as Nafion (Dupont), Aquivion (Solvay Solex Company), and Flemion (Asahi Glass), are widely used in fuel cells due to their chemical stability and high proton conductivity . However, PFSA membranes also have several drawbacks such as the tedious and harsh preparation conditions and release of harmful fluorine …”

Multiblock-copolymerisation-derived sulfonated-poly(p-phenylene)-based polymer electrolyte membranes with simultaneously enhanced proton conductivity and mechanical strength

“…Several groups have reported higher proton conductivities of nanostructured polymer electrolytes than those of random copolymer counterparts. 38–43 Our multiblock copolymers exhibited higher conductivities than those reported previously. These results indicate that the proton conductivity of the nanostructured PEMs was considerably affected by the local structures of the ionic channels.…”

Development of Membranes and Separators to Inhibit Cross‐Shuttling of Sulfur in Polysulfide‐Based Redox Flow Batteries: A Review

“…CEMs with side chains are primarily inspired by Nafion membranes, in which the side chains enhance the mobility of the sulfonic acid groups, which are responsible for the phaseseparation micromorphology (Figure 3d). The growth of these side chains is materialized by introducing side chains to the main polymer backbone through the reaction of phenol groups with the 1,3-porpone sulfate, 1,4-butane sultone, or sodium 6bromohexyl sulfate, [62][63][64][65] as shown in Scheme 4. Additionally, there are other mechanisms to introduce pendant sulfonic acid groups, such as the azide-alkyne click reaction [66] and the nucleophilic substitution reaction mediated by potassium carbonate.…”