Proton Conductivity Variations in Hydrogen-Bonded Crystals Induced by Cyclic Steric Hindrance

Abstract

Hydrogen-Bonded Crystals (HBCs) hold potential as proton conduction materials, yet they face challenges in achieving high proton conductivity, despite their well-defined structures and abundant inherent hydrogen bonding networks. To enhance the proton conductivity, a strategy involving molecule design with cyclic steric hindrance to facilitate proton transfer is proposed. Three HBCs, named HBC-29, HBC-30, and HBC-31 are reported here. HBC-29 and HBC-31 incorporating a cyclic steric hindrance group through a cyclocondensation reaction significantly enhance proton conductivity compared with HBC-30 without a hindrance group. HBC-31 achieves high proton conductivity of 6.18 × 10^–2 S cm^–1 at 60 °C and 95% RH. These findings demonstrate the key role of the cyclic steric hindrance effect in augmenting proton conductivity in HBCs, offering valuable insights for future HBC material design.