Research In Proton Conductive Property Of Polyoxometalate-based Ionic Crystal

Nanoscale polyoxometalates(POMs) with various compositions and structures can be regulated in molecule-level. Thus, polyoxoanions can be viewed transferable blocking units for preparing functional materials. POMs have some advantages in preparing proton conductive materials: first, oxygen atoms of polyoxoanians can be used as proton hopping sites; moreover, polyoxoanions can be regulated in molecule-level to construct proton transfer pathway. Therefore, proton conduction of POM-based ionic crystals was researched.In this paper, a 3D inorganic-organic hybrid proton conductor, [Sm(H2O)5(CO2CH2NH3)2][Al(O H)6Mo6O18]ï¹'10H2O(1), has been synthesized by using coordination cations, [Sm(H2O)5(gly)2]3+(gly =-CO2CH2NH3+), and polyanions, [Al(OH)6Mo6O18]3-([Al Mo6]). The polyanions([Al Mo6]) and the coordination cations([Sm(H2O)5(gly)2]3+) stack to form a 3D supramolecular network structure containing 1D channels along the c axis by electrostatic force and H-bonding. Significantly, the 1D channels are water-filled with a high water content(both Sm coordinated and in lattice). Dynamic adsorption measurements were implemented at 1 atm, and 95% relative humidity(RH). The water adsorption amount(6.51 wt% at 25°C and 5.68 wt% at 80°C) consistent with the number of lattice water molecules of 1 suggests that the water chains were retained at elevated temperatures(80°C) under 95% RH. Alternating-current(AC) impedance measurements of 1 reveal an outstanding conductivity for 1 of 4.53 10-3 S cm-1 at 80°C under 95% RH. The activation energy of 1 calculated from the Arrhenius plots of the proton conductivity is 1.09 e V, which indicated that the protons transfer by a vehicle mechanism.