Confinement of Polymers in Polyoxometalate-based Ion Crystals for Enhanced Proton Conductivity

Abstract

The performance of cation-conducting solid polymer electrolytes is a key to improving the efficiency of fuel cells and secondary batteries. However, commercial polymers such as perfluorosulfonic acids and polyethylene glycols (PEGs) have drawbacks in stability. On the other hand, polyoxometalates (POMs), which are nano-sized anionic metal-oxygen clusters, can efficiently transport protons, while low durability due to hygroscopicity has been a problem. According to these observations, we have synthesized a series of POM-polymer composites as solid proton conductors to overcome these problems. Spectroscopic studies have shown that the segmental motion of the polymers contribute to the proton conduction. Neutron scattering techniques have revealed that a single PEG chain in the crystalline composite with Keggin-type POM stays as a distorted helix in the nanochannel. While numbers of proton-conducting amorphous POM-polymer composites have been reported, these results show both structure-property relationship and high functionality in POM-polymer crystalline composites.