Synthesis and high proton conductivity of an indium-substituted Keggin-type quaternary heteropoly acid

The synthesis and characterization of an indium-substituted quaternary heteropoly acid with a Keggin structure, H4[In(H2O)PW9Mo2O39]·11H2O (PMo9W2In), is reported. At 18 °C under 80% relative humidity, PMo9W2In displays protonic conductivity of 2.32 × 10-4 S cm-1 with an activation energy of 35.52 kJ mol-1, indicating that it is a potential solid protonic conductor following the vehicle mechanism. Its conductivity increases with temperature in the measured temperature range.