Different Protonic Species Affecting Proton Conductivity in Hollow Spherelike Polyoxometalates

Polyoxometalates (POMs), which possess strong acidity and chemical stability, are promising solid proton conductors and potential candidates for proton exchange membrane fuel cell applications. To investigate how factors such as proton concentration and carrier affect the overall proton conduction, we have synthesized new compounds HImMo₁₃₂ (Im, imidazole), HMeImMo₁₃₂, ILMo₁₃₂, and TBAMo₁₃₂ with hollow structures and HImPMo₁₂ with a solid spherelike structure. These crystal models were prepared by encapsulating POM with organic molecules with different proton contents. Among them, the single-crystal sample of the hollow structure HImMo₁₃₂ containing more proton sources shows a high proton conductivity of 4.98 × 10^-2 S cm^-1, which was approximately 1 order of magnitude greater than that of the solid cluster HImPMo₁₂ with the same proton sources and 3 orders of magnitude greater than that of the proton-free organic cation-encapsulated giant ball TBAMo₁₃₂. This study provides a theoretical guidance toward designing and developing new-generation proton conductors and studying their performances at the molecular level.