W. Lee, Kyungwhan Min, Eun Kyu Sun, Hyeonjun Maeng, Junsu Kim, Tae‐Hyun Kim
Hydrogen production via water electrolysis has attracted attention as a key technology for achieving a carbon-neutral society. Anion exchange membrane water electrolysis (AEMWE) has emerged as a promising electrolysis technology, as it combines the benefits of alkaline electrolysis and proton exchange membrane electrolysis. However, the realization of high-performance AEMWE systems necessitates the development of AEMs combining high ionic conductivity with strong alkaline stability. In this study, polymer packing structure and microphase separation were systematically controlled through copolymer composition engineering to obtain AEMs exhibiting balanced water uptake and phase-separated morphology. A series of poly( p -terphenyl- co -biphenyl N -methyl-piperidinium) (PTB- m -QP) copolymers composed of rigid p -terphenyl and rotationally flexible biphenyl units were synthesized with varying biphenyl contents ( m = 0, 25, 50, and 75 mol %). Among them, the PTB-50-QP membrane exhibited the most distinct phase-separated morphology and optimal water uptake, resulting in the highest hydroxide conductivity and alkaline stability, although its relatively high water uptake led to reduced dimensional stability and mechanical strength. To address this limitation, trifluoroisopropyl-functionalized poly( p -terphenyl- co -biphenyl N -methyl-piperidinium) copolymers (PTB-50-QP-F n ) were synthesized ( n = 5 and 10 mol % trifluoroisopropyl). The PTB-50-QP-F5 membrane showed the most well-defined phase-separated morphology, where enhanced hydrophobic interactions among fluorinated groups suppressed swelling and improved dimensional stability and mechanical properties compared with PTB-50-QP. The improved structural stability also enabled higher conductivity retention under strong alkaline conditions and enhanced membrane-electrode interfacial stability. Consequently, the PTB-50-QP-F5 achieved a higher current density of 3.58 A cm –2 at 2.0 V in AEMWE single-cell tests, compared with 1.51 A cm –2 for PTB-50-QP. These results demonstrate that copolymer composition optimization combined with fluorinated group incorporation is an effective strategy for developing high-performance AEMs with improved ionic conductivity, alkaline stability, and mechanical durability for AEMWE applications.