Controlled Assembly of a Hexameric Iridium-Substituted Polytungstate with Excellent Proton Conductivity Performance

With strong water retention and hydrophilic oxygen-rich surfaces for efficient proton transport, polyoxometalate (POM) is an important class of crystalline proton-conducting materials. The POM-based materials have achieved amazing progress in the field of proton conduction. Here, we have successfully constructed an unprecedented purely inorganic Ir-substituted POM K₂Na₁₆H₂₀[(SbW₉O₃₃)₆(W₃IrO₇)₂(W₄O₁₁)]·69H₂O (1) using raw materials as precursors with a traditional one-pot hydrothermal strategy. The crystallographic characterization of compound 1 indicated that it is the largest Ir-substituted POM in the Ir-based POM family and composed of six Keggin trivacant {SbW₉O₃₃} fragments interconnected by two {W₃IrO₇} units and four adjoining {WO₆} octahedra, exhibiting a rare cyclohexane configuration like a boat. Proton conducting measurements of compound 1 showed outstanding proton conductivity with a measured conductivity value of 2.7 × 10^-2 S cm^-1 at 338 K and an 85% relative humidity, along with praisable cycling stability and tolerance. The activation energy of compound 1 in the temperature interval from 318 to 338 K was roughly estimated by the Arrhenius equation to be 0.63 eV (>0.4 eV), providing evidence that the proton transport process of compound 1 followed the vehicle-type mechanism.