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

An indium-substituted Keggin quaternary heteropoly acid, H₄[In(H₂O)PW₉Mo₂O₃₉]·11H₂O, is reported. It owes high protonic conductivity as 2.32 ×10⁻⁴ S cm⁻¹, with 35.52 kJ mol⁻¹ as the activation energy, implying a potential solid protonic conductor.