Methylene-Cross-Linked Poly(biphenyl piperidinium) Anion Exchange Membranes: Enhanced Alkaline Stability and Performance for Water Electrolysis Applications

This study presents the development of a methylene-cross-linked poly(biphenyl piperidinium) anion exchange membrane (AEM) designed to overcome the key limitations of cost, durability, and performance in alkaline water electrolysis applications. The cross-linking strategy employed eliminates the need for expensive β-proton-containing cross-linkers while significantly enhancing both dimensional and alkaline stability of the membrane. Systematic variation of cross-linking density revealed that the optimized 10% cross-linked quaternized poly(biphenyl piperidine) (10XQPBP) membrane exhibits exceptional alkaline resistance with only 15.22% degradation after 3024 h in 2 M KOH at 80 °C, representing substantial improvements over non-cross-linked analogues. The membrane demonstrates superior ionic transport properties with a hydroxide ion conductivity of 132.9 mS/cm at 100 °C, which is three times higher than that of commercial FAA-3-50. Electrochemical performance validation in zero-gap water electrolysis configuration achieved a maximum current density of 1.743 A/cm² at 2.4 V in 1 M KOH at 60 °C, with remarkable operational stability evidenced by a voltage degradation rate of only 0.14 mV/h during continuous operation at 500 mA/cm². The developed cross-linking approach offers a cost-effective pathway to high-performance AEMs, addressing critical barriers to commercial deployment of alkaline electrolyzers for sustainable hydrogen production.