Nature Chemistry, Published online: 01 June 2026; doi:10.1038/s41557-026-02169-8 Achieving simultaneous gains in power density and operational stability in proton-exchange membranes remains a formidable challenge. Now it has been shown that cation-directed assembly and sequential functionalization enable superprotonic polyanion–organic frameworks to serve as multifunctional fillers, delivering both high performance and durability in hybrid membranes for next-generation fuel cells.