Flexibly linked and isomeric piperidinium-based anion exchange membrane with enhanced alkaline stability for durable alkaline water electrolysis

A critical challenge in developing anion exchange membrane (AEM) water electrolysis is to design high-performance AEMs with chemical and mechanical stability under harsh alkaline environments. Herein, we report the rational design and synthesis of QP(T-3-Pip) featuring flexibly linked isomeric piperidinium cations via a Friedel-Crafts polyhydroxyalkylation between terphenyl and commercial 3-piperidinaldehyde. Two key molecular engineering strategies are employed: (i) introducing a methylene linker to relieve ring strain, and (ii) strategically positioning the quaternary nitrogen at the 3-position of the piperidinium ring to suppress β-hydrogen elimination. Compared to the benchmark quaternized poly(terphenyl piperidinium) (QPTP), QP(T-3-Pip) demonstrates substantially improved water uptake (77 %), comparable ionic conductivity and superior tensile strength (∼20 MPa). Notably, QP(T-3-Pip) retains over 78 % of its cationic functionality after 40 days in 5 M KOH at 80 °C, while QPTP shows pronounced degradation after 24 days. During electrolyzer tests using non-noble metal catalysts, QP(T-3-Pip) reveals a high current density of 2.3 A cm −2 at 1.8 V, and exceptional operational durability over 750 h at 1.0 A cm −2 . This work highlights the critical role of piperidinium isomerism and linker engineering in tuning alkaline stability and mechanical integrity, offering a robust and scalable platform for next-generation AEMs in cost-effective alkaline water electrolyzers. • QP(T-3-Pip) featuring flexibly linked isomeric piperidinium cations is synthesized. • QP(T-3-Pip) exhibits an excellent alkaline stability under harsh alkaline conditions comparing with QPTP. • PGM-free AEMFC with QP(T-3-Pip) achieves 2.29 A cm −2 at 1.8 V and 80 °C in 2 M KOH. • PGM-free AEMFC with QP(T-3-Pip) maintains 750-h durability at 1.0 A cm −2 and 60 °C using 1 M KOH.