Ionic polymer–metal composite actuators driven by methylammonium formate for high-voltage and long-term operation

Ionic liquids (ILs) have been exploited as the internal solvent in the development of ionic polymer–metal composite (IPMC) actuators capable of long-term operation. However, a major issue is that most IPMCs impregnated with conventional ILs are yet to be practically applied due to insufficient actuation performance. Herein, methylammonium formate (MAF), an IL with low viscosity, small ionic size, high ionic conductivity, and excellent electrochemical stability, is introduced as a new internal solvent for IPMCs to achieve both excellent operation characteristics and long-term stability. The actuation characteristics of a series of IPMCs impregnated with four types of ILs, including MAF, were analyzed. The MAF-based IPMCs had more than twice the displacement and three-fold higher blocking forces compared with other IL-based IPMCs. Moreover, unlike conventional water-driven IPMCs, the MAF-driven IPMCs operated even at high voltages (4V) without solvent loss and electrolysis. Their initial displacement remained above 81% even after operating for 2160 cycles (6h). This simple change of media in IPMC actuators is expected to advance the design of IPMCs with improved displacement, force generation, and stability.