Quaternary phosphonium-branched poly (aryl piperidinium) membrane with dual anion exchange sites for high-efficiency alkaline water electrolysis

Polyarylpiperidiniums polymers with branched architectures generally exhibit superior electrochemical performance compared to their linear analogs. However, the introduction of cationic groups at branching positions remains largely unexplored. Herein, we designed and synthesized a series of quaternary phosphonium-branched poly (arylene piperidinium) polymers that incorporate aromatic phosphorus units as cationic branching agents, thereby creating dual anion-exchange sites. It is found that the positive charge from the cationic P center is not localized but effectively delocalized across the branched framework, which elevates the electrostatic potential at the piperidinium sites. This delocalization facilitates the hopping of OH⁻ by increasing the probability and lowering the energy barrier for finding the next binding site. Moreover, charge delocalization reduces the charge density at both phosphonium and piperidinium sites, thereby enhancing their resistance to OH⁻ attack and improving overall chemical stability. The resulting membrane achieves an exceptional OH⁻ conductivity of 239.7 mS cm⁻¹and retains high conductivity after 3000 h in 1 M KOH. When applied in an anion-exchange membrane water electrolyzer, it delivers a high current density of 4.75 A cm⁻² and demonstrates stable operation for over 600 h with a low voltage decay rate of 68.9 μV h⁻¹.