Adjusting Competitive Reaction to Control Nucleation and Growth of MnO₂ for a High-Stress Output Electrochemical Actuator

Manganese dioxide (MnO 2 ) with biocompatibility has promising applications in low-voltage electrochemical actuators of implantable medical devices, which can convert electrical energy to mechanical motion. However, the unsatisfactory actuation strain restricts the generation of a larger output stress of MnO 2 for practical application. Herein, a competitive reaction-driven-MnO 2 (CRD-MnO 2 ) nanorod network was fabricated on a nickel (Ni) thin-film substrate by adjusting the component molar ratios. We find that the competitive reaction between 3,4-ethylenedioxythiophene (EDOT) polymerization and oxidation of Mn 2+ controls the nucleation and growth behavior of MnO 2 . The variation in the electron environment, newly generated oxygen vacancies, and a higher content of structural water effectively improve the electroactivity of MnO 2 and simultaneously cause more serious Jahn–Teller (JT) distortion of the crystal octahedrons. Thus, an excellent output performance simultaneously having a much higher actuating strain of 8.3% and an actuation stress of 390.1 MPa is generated during a redox reaction between Mn 4+ and Mn 3+ under 0–1 V. Moreover, the CRD-MnO 2 /Ni composite actuating films assembled on a 3D-printed resin model of a human hand with separated finger joints can perform smooth grasping and releasing actions, demonstrating a huge potential for in vitro rehabilitation exercises and implantability for people with finger dyskinesia. This work provides a strategy for actuator material fabrication by controlling a nucleation and growth process by adjusting a competitive reaction.