Kosmotrope-Promoted Proton Hopping in Supramolecular Conductors

Scientific interest in the Hofmeister effect has waxed and waned since its discovery over a century ago; however, its ion-specific influence on solvation and molecular organization remains a topic of enduring significance. While extensively studied in aqueous systems, its relevance to solid-state materials and Grotthuss mechanisms has remained largely unexplored. Here, we unveil a class of supramolecular organic cage salts, the Cage1 series, with counteranions spanning the Hofmeister series to systematically probe their ion-specific effects on solid-state proton conduction. Kosmotropic anions, stabilized by the supramolecular organic cage, are found to markedly enhance proton conductivity, promoting the formation of an extended hydrogen-bonded network (HB-network) that facilitates Grotthuss-type proton hopping. The conductivity increases by over 2 orders of magnitude from chaotropic Cage1-HI to kosmotropic Cage1-H₂SO₄, reaching up to 1.03 × 10^-1 S cm^-1 at 333 K under 95% RH. Single-crystal and molecular dynamics (MD) analyses reveal how distinct cage-anion-water interactions modulate proton mobility at the molecular level. These findings establish an unprecedented link between Hofmeister chemistry and proton transport in solids, offering a new ion-specific design principle for next-generation supramolecular proton conductors.