The effect of MWCNT content on electropolymerization of PPy film and electromechanical behavior of PPy electrode-based soft actuators

This study investigates the effects of multi-walled carbon nanotubes (MWCNTs) content on the electropolymerization potential of polypyrrole (PPy) on both surfaces of carbon nanoparticle/MWCNT (CN/M)-coated Nafion membranes and on the electrical, electrochemical and electromechanical properties of PPy- electrode based soft actuators. SEM analysis revealed that the surface morphology of actuators changes considerably by altering the MWCNT content and the most porous PPy films formed in actuator comprising of 25 wt% MWCNT. The electrochemical characteristics of the prepared actuators were compared in terms of double layer capacitance (Cdl), pseudo capacitance (CF) and ionic conductivity (σ). The capacitive nature of the prepared actuators was followed by waveform analysis of applied voltage and output current. Cdl and σ increased by increasing the MWCNT content up to 25 wt% and afterward decreased considerably, while a reverse trend was observed for CF. The electrochemical impedance spectroscopy (EIS) measurements confirmed that this sample had the highest surface roughness. These data were in good agreement with the data obtained from water uptake (WUP) and ion exchange capacity (IEC) measurements. The electro-chemo-mechanical performances of the actuators were followed by studying the maximum tip displacement and IV curves. The largest tip displacement was obtained in actuators comprising of 25 wt% MWCNT which showed to have the highest capacitive characteristic (243.52 mF. cm− 2). The specific electro-mechanical energy efficiency (1.18) and the maximum tip displacement (25 mm) of these metal-free actuators were 18% and 9% higher than that considered for Pt-based actuators, respectively. This strategy is therefore of considerable interest for increasing the applicability of low cost carbon-based soft actuators in medicine and robotics.