Piperidinium-crosslinked block copolymer anion exchange membranes: Effect of crosslinking degree on membrane properties and water electrolysis performance

초록

Anion exchange membranes (AEMs) are key components in anion exchange membrane water electrolysis (AEMWE) and require both high ionic conductivity and long-term durability. In this study, a quaternizationbased crosslinking strategy was employed using 4,4 '-trimethylenebis(1-methylpiperidine) (TMBMP), a chemically stable crosslinker under alkaline conditions, to enhance the ion exchange capacity (IEC), suppress membrane swelling, and improve alkaline stability. Polystyrene-b-poly(6-bromohexyl acrylate)-b-polystyrene (PSBHAS) block copolymers with various polystyrene contents (30, 44, 50, and 60 wt%) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, and four types of crosslinked PSBHAS membranes (CPSBHAS30, CPSBHAS44, CPSBHAS50, and CPSBHAS60) were prepared to investigate the correlation between the degree of crosslinking and membrane properties. As the degree of crosslinking increased, both IEC and microphase separation improved. As a result, CPSBHAS30, with the highest degree of crosslinking, exhibited the highest hydroxide ion conductivity of 67.4 mS/cm at 80 degrees C. However, considering the core properties required for long-term durability, CPSBHAS50 exhibited the most balanced performance. CPSBHAS50 exhibited a low swelling ratio (22.6 % at 80 degrees C), high tensile strength (17.6 MPa), and excellent alkaline stability, retaining 86.7 % of its initial hydroxide ion conductivity after 720 h of immersion in 1 M KOH at 60 degrees C. Furthermore, under AEMWE operating conditions (1 M KOH, 60 degrees C, 2.0 V), it achieved a higher current density (0.926 A/cm2) than the commercial FAA-3-50 membrane (0.854 A/cm2) and maintained stable voltage operation for over 100 h at a constant current of 0.2 A/cm2, demonstrating significant practical performance.

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