Humidity-Gated Dual Proton–Electron Conduction in a Redox-Active Ionic Hydrogen-Bonded Organic Framework

Abstract

Hydrogen-bonded organic frameworks (HOFs) are promising proton conductors because of their hydrogen-bond networks. However, single-phase HOFs that conduct both protons and electrons remain rare. We report an ionic HOF, iHOF-100, assembled from an anthraquinone disulfonate anion and a bipyridinium diamine cation. Its single-crystal structure shows two carrier pathways along the a-axis: a charge-assisted hydrogen-bond network for proton conduction and π–π stacks of redox-active units for electron hopping. Electrochemical impedance spectroscopy and direct-current measurements reveal humidity-gated dual proton–electron conductivity. At 30 °C and 33% RH, only low proton transport occurs, and the material is electronically insulating. At 98% RH, dual transport emerges, with proton and electron conductivities reaching 1.19 × 10–1 and 5.61 × 10–3 S cm–1, respectively. Kinetic isotope effects (>4) support a proton-gated hopping mechanism. Density functional theory identifies bipyridinium and anthraquinone as redox hubs. Integrating charge-assisted hydrogen-bond networks with redox-active groups provides a strategy for dual proton–electron conductors.