Sequential Monomer Addition Regulates Hydration in Branched Poly(aryl piperidinium) Membranes for Water Electrolysis

The conductivity-swelling trade-off limits anion exchange membranes (AEMs) for water electrolysis. Here, we investigated how the timing of tetraphenylmethane (TPM) incorporation influences precursor assembly and membrane hydration in poly(aryl piperidinium) AEMs. Introducing TPM before backbone extension alters precursor formation and favors a more uniform distribution of hydrophilic domains in the resulting membranes. Spectroscopic and NMR analyses further associate this route with enhanced hydrogen-bond organization and increased local mobility within the hydrated membranes. The optimized P-TPM5 membrane reaches an OH– conductivity of 229.4 ± 6 mS cm–1 at 80 °C while maintaining a swelling ratio of approximately 15%. In an AEM water electrolyzer containing a NiFe-LDH anode and Pt/C cathode, the membrane delivers 5.74 A cm–2 at 2.0 V and operates for more than 1100 h in a staged-current test. These results identify the timing of branching-unit incorporation as a synthesis variable for tailoring hydration environments and improving the conductivity-swelling balance of AEMs.