Electrochemical and electromechanical behavior of Nafion-based soft actuators with PPy/CB/MWCNT nanocomposite electrodes

Abstract

In this work, as an alternative to precious platinum electrodes in IPMC actuators, PPy/CB/MWCNT electrode actuators were successfully fabricated by electropolymerization of PPy on both sides of the CB/MWCNT-coated Nafion membranes. Electropolymerization of PPy was performed using cyclic voltammetry (CV) and chronopotentiometry (CHP) in water and acetonitrile (AN) to study the effect of the synthesis parameters on the physical, electrochemical and electromechanical characteristics of actuators. The electrochemical characteristics of the actuators were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The physical and structural properties of the actuators were characterized using scanning electron microscopy (SEM), water uptake (WUP) and ion exchange capacity (IEC) determination methods. SEM analysis revealed that the surface morphology of actuators changes considerably by altering the synthesis parameters and that the finest cauliflower-like structure of the PPy film is formed in actuators prepared in AN using the CHP technique. These metal-free actuators showed ionic conductivity (29.88 mS cm⁻¹) and capacitive characteristics (39.23 μF) about eleven and thirty six times higher than that considered for Pt-based IPMC actuators, respectively. The deposition of PPy/CB/MWCNT electrodes on the Nafion membrane also resulted in higher WUP (79.9%) and IEC (6.7 meq g⁻¹) of the actuators, confirming the hydrophilic nature of the PPy-based electrodes. The maximum tip displacement of these actuators (at optimized conditions) was however about 26% lower than that of Pt-based IPMC actuators which can be improved by decreasing the thickness and surface resistance of the PPy film via altering the synthesis parameters.