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.