Naphthalenedisulfonic Acid-Regulated Ionic HOFs Enabling Single-Crystal Superprotonic Conductivity

Abstract

Designing ionic hydrogen-bonded organic frameworks (iHOFs) with single-crystal superprotonic conductivity is of great significance for unraveling the mechanisms of proton-conductive materials at the molecular level. To regulate proton transport pathways, we synthesized two novel ionic hydrogen-bonded organic frameworks, iHOF-60 and iHOF-61, by adjusting the spatial configuration of the sulfonate groups. Both materials exhibit three-dimensional hydrogen-bonding networks and highly anisotropic proton conductivity, and clear proton transport pathways were identified through single-crystal structure analysis. Notably, experimental results show that iHOF-60 achieves a proton conductivity of up to 0.216 S cm−1 along the a-axis at 80 °C and 85% relative humidity, demonstrating exceptional superprotonic conduction performance. Density functional theory (DFT) calculations further confirm that iHOF-60 possesses superior proton transport properties compared to iHOF-61, which is attributable to its more continuous hydrogen-bonding network, smoother proton-transport pathway, and lower steric hindrance. These findings provide new experimental and theoretical insights for the design of high-performance proton-conducting materials.