Hexaphenylbenzene Nodes Reshape Hydroxide Transport Energetics in Rigid Microporous Membranes

Abstract

Rigid microporous anion exchange membranes (AEMs) can create continuous hydroxide transport pathways while suppressing swelling, but geometric percolation alone does not ensure rapid ion migration in chemically confined pores. Here we show that hydroxide transport in rigid microporous ionomers can be accelerated through topological ionic nodes that regulate local transport energetics. Incorporation of hexaphenylbenzene (HPB) into an ether-free poly(aryl piperidinium) framework simultaneously generates interconnected microporosity and spatially correlates multiple cationic sites within pore walls. Density functional theory and free-energy analysis show that HPB weakens hydroxide binding and lowers intersite hopping barriers by smoothing the local energetic landscape under confinement. The optimized membrane reaches 168.6 mS cm–1 at 90 °C, exhibits an apparent activation energy of 12.7 kJ mol–1, and swells by only 12.1% despite 75.6% water uptake. It retains 97.4% of its conductivity after 2000 h in 2 M KOH at 90 °C. These advantages translate into a peak fuel cell power density of 2.50 W cm–2 and an electrolyzer current density of 8.05 A cm–2 at 2.0 V, with stable operation over 2500 h. Spatially correlated ionic nodes therefore provide a molecular strategy to regulate hydroxide transport energetics in rigid microporous ionomers.