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

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-H 3 L ) (H 3 L = [3-(4-methyl-benzoyl)-thioureido]-acetic acid; CH 3 C 6 H 4 C(O)NHC(S)NHCH 2 COOH) and its related 3D copper MOF, {[Cu I 3 Cu II 3 L 3 (DMF) 2 (CH 3 OH)(H 2 O)]·3CH 3 OH} n ( 1 ). Both HOF-H 3 L 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-H 3 L (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. The proton conduction in one HOF and related MOF have been investigated and discussed.