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.