Enhancing Proton Conductivity in a 3D Metal–Organic Framework by the Cooperation of Guest [Me2NH2]+ Cations, Water Molecules, and Host Carboxylates

A novel proton-conducting MOF material has been synthesized by using 3,3′,4,4′-biphenyltetracarboxylic acid (H 4 bptc) as organic ligands, which linked to four [Zn(COO) 4 ] 2– secondary building units and K ions through four carboxyl groups, and generated a 3D framework [Zn 3 K 2 (bptc) 3 (DMF) 2 ][Me 2 NH 2 ] 4 ( JLU-Liu44 ). The proton-conducting properties of JLU-Liu44 were investigated by impedance spectroscopy. JLU-Liu44 exhibits low conductivity under anhydrous conditions, but the proton conductivity under humidified conditions was significantly enhanced due to the cooperation of guest [Me 2 NH 2 ] + cations, water molecules, and host carboxylates. JLU-Liu44 exhibits high proton conductivity of 8.4 × 10 –3 S cm –1 at ambient temperature (27 °C) and 98% relative humidity; it is comparable to the most reported proton-conducting MOFs materials under the same condition for powdered sample. The activation energy ( E a ) obtained from an Arrhenius plot was 0.25 eV, indicating that the proton conduction behaviors occur through a Grotthuss mechanism.