Crystalline polyoxometalate (POM)–polyethylene glycol (PEG) composites aimed as non-humidified intermediate-temperature proton conductors

Crystalline polyoxometalate (POM)–polyethylene glycol (PEG) composites aimed as non-humidified intermediate-temperature proton conductors were synthesized and characterized by single crystal and powder XRD, solid state MASNMR, and TG-DTA measurements. Among the POM–PEG composites, Cs2.7H0.3[PW12O40]·1.2PEG1000 (CsHPW-PEG1000) possessed one-dimensional channels with diameters of ca. 6 and 8 Å, where PEG probably resided, and showed the best performance as a proton conductor (1.2×10−5 S cm−1 at 443 K). Proton conductivities of POM–PEG composites decreased by the increase in molecular weights of PEG (CsHPW-PEG 12,000) or anion charges (CsHSiW-PEG1000). Variable contact time 13C-CP (cross polarization) MASNMR revealed that local mobility (i.e., segmental motion) of PEG is related to the trends in proton conductivities. These results show that amount of acidic protons (H+) is not the primary factor in proton conduction and that segmental motion of PEG assists the proton hopping among POMs in the crystal lattice of POM–PEG composites.