Imidazolium functionalized block copolymer anion exchange membrane with enhanced hydroxide conductivity and alkaline stability via tailoring side chains

Abstract

To develop polymer electrolyte membrane with both high hydroxide conductivity and good alkaline stability, series of poly(arylene ether sulfone)s block copolymers bearing varied imidazolium functionalized aromatic pendants are synthesized, and the relationship between ionic pendants and the membrane properties are investigated and discussed. Atomic force microscopy (AFM) results suggest that, the well-controlled block copolymers and pendent aromatic chain structures are responsible for the formation of the well-defined microphase-separated morphology which is benefit to construct highly conductive ionic transport channels in membrane. The membranes tethering longer imidazolium functionalized aromatic pendants (Im-DFDM-bPES) exhibit large hydroxide conductivity than those bearing shorter ones (Im-DFDB-bPES) in spite of their comparable IEC values, this is in accordance with their sizes of hydrophilic domains in membrane. Among the membranes, Im-DFDM-bPES-x7y32 with IEC of 1.30 mequiv g−1 gives the highest hydroxide conductivity (34.2 and 98.7 mS cm−1 at 25 and 80 °C, respectively). Besides, both Im-DFDM-bPES and Im-DFDB-bPES membranes exhibit high alkaline stability after aging under severe conditions (4 M NaOH at 80 °C) for 144 h, where the aged Im-DFDM-bPES and Im-DFDB-bPES give hydroxide conductivity remaining by 74.8%–77.2% and 64.5%–66.4%, mechanical properties with maximum stress of 47.36–51.30 MPa and 60.03–62.28 MPa, respectively, indicating good chemical stability of both imidazolium moiety and block copolymer backbone.