Incorporation of Poly(vinyl alcohol) into an Inorganic Framework Based on Eu-Bonded Preyssler-Type Phosphotungstate for Enhanced Proton Conduction

To construct an environmentally friendly crystalline proton conductor and establish a composition–structure–function relationship, polyoxometalate and poly(vinyl alcohol), an anionic metal-oxide cluster, and a polymer with hydroxyl groups, respectively, providing proton carriers and conduction pathways, were combined with a lanthanide ion with a large coordination sphere to trap water effectively. The crystalline composite exhibited a high proton conductivity of 8.3 × 10–3 S cm–1 at 368 K and 75% relative humidity. We demonstrate the potential for achieving high performance under mild humidification with a simple polymer like poly(vinyl alcohol).