Abstract
A class of phenolphthalein anilide (PA)-based poly(ether sulfone) multiblock copolymers containing pendant quaternary ammonium (QA) and imidazolium (IM) groups were synthesized and evaluated as anion exchange membrane (AEM) materials. The AEMs were flexible and mechanically strong with good thermal stability. The ionomeric multiblock copolymer AEMs exhibited well-defined hydrophobic/hydrophilic phase-separated morphology in small-angle X-ray scattering and atomic force microscopy. The distinct nanophase separated membrane morphology in the AEMs resulted in higher conductivity (IECw = 1.3–1.5 mequiv./g, σ(OH−) = 30–38 mS/cm at 20 °C), lower water uptake and swelling. Finally, the membranes were compared in terms of microbial fuel cell performances with the commercial cation and anion exchange membranes. The membranes showed a maximum power density of ~310 mW/m2 (at 0.82 A/m2); 1.7 and 2.8 times higher than the Nafion 117 and FAB-PK-130 membranes, respectively. These results demonstrated that the synthesized AEMs were superior to Nafion 117 and FAB-PK-130 membranes.
Highlights
Due to the higher transport of cations other than protons through cation exchange membrane (CEM) (e.g., Nafion) which usually leads to pH splitting into the chambers, anion exchange membrane (AEM) are seen as an alternative for use in microbial fuel cells (MFCs)
The multiblock copolymers can self-assemble into well-defined hydrophobic/hydrophilic phase separation where the hydrophilic domain creates pathways for ion transport while the hydrophobic domains provide mechanical stability
A new series of phenolphthalein-based multiblock poly(arylene ether sulfone) AEMs were synthesized by block polycondensation, bromination, and quaternization
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In our previously synthesized membranes [12], controlled ordering of the sequenced hydrophilic and hydrophobic blocks in multiblock copolymers led to distinct well-defined hydrophilic/hydrophobic phase-separated morphology which resulted in higher ion conductivity, lower uptake and swelling. In a slightly different technique, Rao et al [19] used benzylmethyl bromination to synthesize imidazolium functionalized phenolphthalein-based poly(ether sulfone) AEMs which exhibited high thermal stability and ion conductivity (PI-PES, ~100 mS/cm at 80 ◦ C). The AEMs are synthesized by a low-temperature polycondensation (using HFB as a linkage group) reaction between telechelic oligomer blocks to synthesize a precursor multiblock copolymer followed by benzylmethyl bromination and quaternization. The AEMs are synthesized by a low-temperature polyconden of 22 sation (using HFB as a linkage group) reaction between telechelic oligomer blocks to synthesize a precursor multiblock copolymer followed by benzylmethyl bromination and quaternization.
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