Regio‐Regularity as a Decoupled Design Axis for Anion‐Exchange Ionomeric Binders of Anion‐Exchange‐Membrane Water Electrolysis

ABSTRACT Anion‐exchange‐membrane water electrolysis (AEMWE) offers a low‐cost route to green hydrogen, but electrode performance remains constrained by anion‐exchange ionomer (AEI) binders. Although aromatic poly(aryl piperidinium) (PAP) AEIs provide high alkaline stability, their rigid backbones often restrict active‐site accessibility. Here, we identify the regio‐regularity (RR) of an asymmetric biphenyl unit as a design axis that is decoupled from cation chemistry, ion‐exchange capacity, and backbone family, and that tunes catalyst–binder coupling through backbone twist, alkyl density, and chain packing. A series of poly(2,2′‐dipropyl‐biphenyl‐co‐biphenyl‐co‐terphenyl piperidinium) binders (RR X , X = 22‒100) is synthesized via superacid‐catalyzed polyhydroxyalkylation. Bulk, half‐cell, and single‐cell AEMWE characterizations reveal a non‐monotonic RR dependence with an optimum in the intermediate‐RR region (RR42–RR62). This intermediate‐RR binder forms cohesive, thermally adaptive ion channels and exhibits the lowest apparent charge‐transfer resistance among the tested binders. As a cathode binder, RR62 delivers 1.98 V at 3 A cm −2 in 0.1 M KOH. Furthermore, RR62 shows a significantly lower voltage degradation rate than a commercial PiperION reference over 500 h at 0.5 A cm −2 in 0.5 M KOH, and sustains 200 h of solar‐mimicking load cycling, peaking at 2.23 A cm −2 , establishing backbone regio‐regularity as a backbone‐family‐decoupled lever to co‐optimize activity and longevity.