Multiday operable ionic polymer-metal composites prepared using a stacking method for practical actuator applications

Ionic polymer-metal composites (IPMCs) with water as an internal solvent (water-IPMCs) lose all their function after 20 minutes of actuation due to water depletion, despite superb initial performance. Studies have attempted to replace water with ionic liquid (IL), but conventionally made IL-based IPMCs (conventional IL-IPMCs) maintained only a quarter of displacement and blocking force of water-IPMCs. Here, we propose a new method in which a polymer membrane is soaked with IL at high temperatures, and then stacked between two individually-prepared electrode layers. The layers were combined through compression, and the resulting IPMCs (stacked IL-IPMCs) had a surface resistance 10 times lower than conventional IL-IPMCs, and showed actuation performance comparable to water-IPMCs. More importantly, stacked IL-IPMCs maintained more than 95% of their performance even after several days of actuation. This is a level of stability that has not been reported and therefore a huge breakthrough in the development of IPMC actuators. • Ionic liquid-based IPMC was made by stacking individual layers of Nafion and Pt • Soaking Nafion in IL at high temperature raised its swelling and ionic conductivity • Stacking method prevented electrode damage, lowering the surface resistance of IPMC • Reduced resistance and enhanced capacitance enabled superb actuation performance • Multiday operation of IPMC was achieved due to electrochemical stability of IL