Synthesis and conductive performance of indium-substituted ternary heteropoly acids with Keggin structures

Abstract

Two new high-proton conductors, indium-substituted ternary heteropoly acids with Keggin structures, H₄[In(H₂O)PW₁₁O₃₉]·11H₂O and H₅[In(H₂O)SiW₁₁O₃₉]·8H₂O, have been synthesized and characterized using elemental analysis, IR, UV, XRD and TG-DTA. Their proton conductivities were measured using electrochemical impedance spectroscopy (EIS), and the results indicate that H₄[In(H₂O)PW₁₁O₃₉]·11H₂O and H₅[In(H₂O)SiW₁₁O₃₉]·8H₂O are solid high-proton conductors with a conductivity of 2.60 × 10⁻⁴ S cm⁻¹ and 5.25 × 10⁻⁴ S cm⁻¹, respectively, at 18 °C and 80% relative humidity (RH). Their activation energies are 33.40 kJ mol⁻¹ and 28.52 kJ mol⁻¹, which suggests that the mechanism of proton conduction is the vehicle mechanism. In the range of the measured temperatures, the conductivity of both heteropoly acids increases with higher temperatures.