A path to improve proton conductivity: from a 3D hydrogen-bonded organic framework to a 3D copper-organic framework

Abstract

To conduct a comparative study on proton conductivities of a hydrogen-bonded organic framework (HOF) and its related metal–organic framework (MOF), we selected and fabricated a 3D HOF (HOF-H₃L) (H₃L = [3-(4-methyl-benzoyl)-thioureido]-acetic acid; CH₃C₆H₄C(O)NHC(S)NHCH₂COOH) and its related 3D copper MOF, {[Cu^I₃Cu^II₃L₃(DMF)₂(CH₃OH)(H₂O)]·3CH₃OH}_n (1). Both HOF-H₃L and MOF 1 exhibit high water stability. Their proton conductivities under different relative humidities (RHs) were fully investigated. Note that the MOF 1 exhibited the optimized conductivity of 3.78 × 10⁻⁴ S cm⁻¹ that was nearly one order of magnitude larger than that of HOF-H₃L (6.91 × 10⁻⁵ S cm⁻¹) at 100 °C and 98% RH. Based on the crystal data, E_a calculations, water vapor absorptions and PXRD patterns, the proton-conducting mechanisms were suggested. This comparative investigation provides a new inspiration to researchers to design new proton-conductive materials in the future.