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

Abstract

Crystalline polyoxometalate (POM)-polyethylene glycol (PEG) composites aimed as nonhumidified 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 onedimensional 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 © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 of POM-PEG composites decreased by the increase in molecular weights of PEG (CsHPW-PEG12000) or anion charges (CsHSiW-PEG1000). Variable contact time 13 C-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.

Polyoxometalate/Polyethylene Glycol Interactions in Water: From Nanoassemblies in Water to Crystal Formation by Electrostatic Screening

“…Hence, composite materials of POM and EO x oligomers may become important as the combination of both the catalytic performance of POMs and above mentioned benefits of PEG could lead to advantageous materials with superior performances. Therefore, lots of work has already been performed on this subject . In 1989, Neumann et al.…”

“…In materials science, layered PEG–POM structures consisting of PEG chains covalently grafted to a POM, have been constructed . Only recently, non‐covalently bound POM–PEG composites were produced through a hydrothermal route and characterized as intermediate temperature proton conductors …”

“…Therefore, lots of work has already been performed on this subject. [35][36][37][38][39] In 1989, Neumann et al observed an elevated catalytic activity of POMs in the presence of PEG. [39] In materials science, layered PEG-POMs tructures consisting of PEG chains covalently grafted to aP OM, have been constructed.…”

“…[36,37] Only recently,n on-covalently bound POM-PEG composites were produced through ah ydrothermal route and characterized as intermediate temperature proton conductors. [38] In the present work, PEG-PW interactions were probed in water at room temperature anda tl ow concentrations (< 100 mm), much below the solubility limits of the components, by varying the chain length of PEG for as eries of compounds from pure EO 1 to EO 4 .L onger EO x weret ested as well but as they are difficult to obtain with ap ure grade, industrial mixtures wereu sed:P EG200 (equivalenti na verage to EO 4 ), PEG300 (% EO 6 ), PEG400 (% EO 8 ), and PEG20000( % EO 400 ). Industrial grade PEG x show dispersity in their chain lengths, that is, in their number of EO units.…”

Conductive Supramolecular Architecture Constructed from Polyoxovanadate Cluster and Heterocyclic Surfactant

“…Heteropolyacids, Keggin-type POMs with a proton as counter cation, have been investigated as high proton conductors [20][21][22][23][24][25][26]. Such POMs have been successfully hybridized by surfactant cations to form inorganic-organic hybrids [27][28][29][30][31][32][33][34][35] and single crystals [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55].…”