Importance of Flexibility in Polymerized Ionic Liquid-Coated Nanoparticles for HT-PEFC

Polymer electrolyte membranes (PEMs), which combine nanoparticles or nanofibers with ion-conductive polymers, have demonstrated enhanced mechanical properties, thermal stability, and ionic conductivity, while enabling the formation of continuous ion-conducting channels. Ionic liquids (ILs) have attracted attention as ionic conductors for high-temperature and nonhumidified environments. However, the high fluidity of ILs causes them to leach out from the PEMs, reducing ionic conductivity. Therefore, stabilizing ILs within the PEM matrix is essential. In this study, core–shell nanoparticles were prepared by coating silica nanoparticles with a polymerized ionic liquid (PIL). The influence of the content of 1-vinylimidazole, a key component of the PIL, on ionic conductivity was evaluated. The prepared core–shell nanoparticles achieved a maximum ionic conductivity of 2.3 × 10–4 S/cm (160 °C, 0% RH). Furthermore, the flexibility of the PIL was found to enhance the ionic conductivity. These findings can inform the design of PEM materials incorporating PILs for effective operation under high-temperature and nonhumidified conditions.