Investigation of bi-ionic contribution for the enhancement of bending actuation in polypyrrole film

Electrochemomechanical deformation (ECMD) in the electrodeposited polypyrrole (PPy) films was examined by judicious selection of the supporting electrolytes during electropolymerization and cyclic voltammetry (CV). A critical perusal of the ECMD characteristics corroborates the cation-driven and/or anion-driven deformation in the PPy films. It was found that a freestanding PPy film successively electrodeposited as a cation-driven layer followed by an anion-driven layer works as a bimorph actuator. The large bending motions were observed in 1 M NaCl solution in which both anion-driven and cation-driven layers are electroactive. In contrast, the bending motions were found to be suppressed in both 1 M ethylbenzene sulfonic acid sodium salt and 1 M tetrabutylammonium chloride, in which only one of the cation-driven or the anion-driven layer is electroactive. The results indicate that the bimorph actuator driven by the synchronized insertion and deinsertion of anion and cation, which can be expressed as the bi-ionic actuator, clearly enhances its bending motion compared to that observed in the conventional bimorph actuators driven by mono-ionic ECMD behaviors.