Soybean Root-Inspired SWCNT/Ag@Au Composite Electrode for Ionic Polymer–Metal Composite Actuators

Ionic polymer–metal composites (IPMCs), as innovative soft smart polymers, can effectively convert electrical energy into mechanical energy through electrochemically induced ion migration, demonstrating significant potential in soft intelligent robotics. As the actuation characteristics of IPMC actuators are largely determined by the electrochemical kinetics within the electrodes, it is highly desired to fabricate tailored electrodes with excellent electrical conductivity and superior electrochemical characteristics to develop high-performance IPMC actuators. Taking inspiration from the distinctive structure of soybean roots, we propose the concept of developing a soybean root-style composite electrode consisting of single-walled carbon nanotubes, silver nanoparticles, and gold nanoparticles for IPMCs using a combination of spray coating and electroplating technologies. The developed electrodes have a unique hierarchical structure, low surface resistance (2.80 Ω/sq), and greatly enhanced electrochemical characteristics because of the redox reactions of silver nanoparticles during the actuation process, which would facilitate the ion migration and storage in actuation. Accordingly, the resulting IPMC actuator outputs excellent electromechanical work under 2 V voltage, including large peak-to-peak deformation (displacement 14.91 mm, strain 0.94%), high deformation rate (1.07 mm/s), wide frequency response (0.01–10 Hz), and high generated stress (3.67 MPa). The IPMC actuators can be used to construct flexible artificial fingers, enabling efficient grasping and transport of delicate flowers without causing any damage to their surfaces. This study provides insight into the design and optimization of composite electrode materials for advanced IPMC actuators with improved functional capabilities in various applications.