Isomeric Poly(arylene piperidinium) Electrolyte Membranes with High Alkaline Durability

Abstract The isomerization strategy is employed to enhance the alkaline stability of poly(arylene piperidinium)s (PAP) while maintaining the monomer commerciality and polymer architecture tunability. Isomeric poly(arylene piperidinium) (i‐PAP) exhibits improved alkali resistance relative to conventional PAP, as evidenced by ex situ alkaline stability and in situ cell durability tests. Following treatment in 10 m aqueous NaOH at 80 °C for 360 h or operation at 0.4 A cm⁻² for 100 h in an anion exchange membrane fuel cell (AEMFC) prototype, the decomposition of the piperidinium moieties in i‐PAP is ≈50% of that observed in PAP. Moreover, through a copolymerization strategy, the i‐PAP‐88 membrane, which has suppressed water absorption, reaches a peak power density of 1.44 W cm⁻² and demonstrates an in situ durability of 310 h. Furthermore, a noble metal‐free (anode) AEM water electrolyzer (AEMWE) achieves a high current density of 6.43 A cm⁻² at 2.0 V and an excellent Faradaic efficiency of 98.3%. This study highlights a strategy for designing alkali‐stable polyelectrolytes that mitigate degradation during the operation of alkaline electrochemical devices.