Different Protonic Species on Affecting Proton-Conductivity in Hollow Sphere-Like Polyoxometalates.

The polyoxometalates (POM), which possess strong acidity and chemical stability, are promising solid proton conductors and potential prospects for proton exchange membrane fuel cell applications. To investigate how the factors such as proton concentration and carrier affect the overall proton conduction, we have synthesized the new compounds, HImMo132 (Im: imidazole), HMeImMo132, ILMo132 and TBAMo132 with hollow structures and HImPMo12 with solid sphere structure. Those crystal models were prepared by POM encapsulated 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 one order of magnitude greater than the solid cluster HImPMo12 containing the same proton sources, and three orders of magnitude greater than 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.