High proton conduction in two highly stable phenyl imidazole dicarboxylate-based Cd(II)-MOFs

In recent years, carboxylic acid-based MOFs have gathered a lot of attention because of their high stability and excellent proton conductivity, and are likely to be promising candidates as proton-exchange membranes. In this work, we synthesized two MOFs by reference method, namely [Cd4(μ3-PhIDC)2(μ4-PhIDC)2(H2O)]n (1) (H2PhIDC ​= ​2-phenyl-4,5-imidazole dicarboxylic acid), [Cd2(μ2-PhIDC)2(phen)2]n (2) (phen ​= ​1,10-phenanthroline), which have high water stability. Therefore, this work focuses on their intrinsic proton conductivity. The results showed that under the conditions of 98% RH/100 ​°C, the proton conductivities of 1 and 2 can achieve 2.71 ​× ​10−3 and 2.67 ​× ​10−3 ​S ​cm−1, respectively. Finally, based on the structural analysis and calculations of activation energies, the principle of proton transfer is inferred, which will afford new inspiration for the design of the proton conduction crystalline materials.