Cation-directed assembly and sequential functionalization enable superprotonic polyanion-organic frameworks for high-power fuel cells.

Proton-exchange membranes are critical for high-performance fuel cells, yet simultaneous enhancement of their power density and operational stability remains challenging. Here we introduce a supramolecular engineering approach for constructing polyoxometalate-organic frameworks through precise integration of trigonal-shaped cationic tectons and polyoxometalate anions. Size-matched anchoring of polyoxometalates via directional C-H···anion hydrogen bonds-enabled by shape-persistent tectons-creates ordered one-dimensional channels lined with imidazolium groups. Post-synthetic modification with sulfonate groups enabled our frameworks to achieve high proton conductivity, with proton transport governed by channel-selective hydration, percolated hydrogen-bond networks and host-guest interactions under confinement. The porous ionic structure and flexible hybrid nature of these frameworks provide exceptional solution processability and compatibility with polymer matrices. Integration into Nafion resins dramatically enhances the proton conductivity and chemical stability of the resulting hybrid membranes, as well as enhancing the peak power density and current density over commercial Nafion. This strategy provides a promising blueprint for developing fillers in proton-exchange membrane design to advance fuel cells towards decarbonization targets.