Fluorenyl phenolphthalein groups containing a multi-block copolymer membrane for alkaline fuel cells

Abstract

An anion-conducting aromatic multi-block copolymer (PEs-A_xB_y) was synthesized by a block co-polycondensation reaction between fluorene and phenolphthalein containing oligomers. The quaternized multi-block copolymers (QPEs) resulted in ductile transparent membranes with well-ordered multi-block structures. In chloroform, a thin polymer film (PE-A₂₂B₂₄) with hexagonal well-ordered geometry was obtained. Meanwhile, in NMP/DMAc a dense thin film for QPE-A₂₂B₂₄ was obtained. As an additional attractive feature, the pore structure and pore-geometry of the membrane thin film may be controlled by the membrane casting medium and conditions. The presence of hydrophilic (biphenyl fluorene)–hydrophobic (connector)–hydrophilic (phenolphthalein) groups was responsible for phase separation, and interconnected ion conducting pathways. Among many synthesized anion exchange membranes (AEMs), QPE-A₂₂B₂₄ exhibited excellent stabilities, 0.95–2.24 meq g⁻¹ ion exchange capacity and 95 mS cm⁻¹ conductivity, at 80 °C. The reported AEM retained the conductivity after 1000 h of boiling treatment. QPE-A₂₂B₂₄ membranes were assessed as suitable candidates for alkaline fuel cell applications.