Cyclic step-voltammetric analysis of cation-driven and anion-driven actuation in polypyrrole films

Cation-driven and anion-driven electrochemomechanical deformations (ECMD) in electrodeposited polypyrrole (PPy) films have been investigated by means of cyclic voltammetry and cyclic step-voltammetry (CSV). The film deposited from hydrochloric acid (PPyCl) expanded upon anodic reaction (anodic expansion) while that deposited from dodecyl-benzene sulfonic acid (PPyDBS) exhibited cathodic expansion. In the case of the film deposited from p-phenol sulfonic acid (PPyPPS), it was found to show the anodic expansion at 600 mV (vs Ag wire as a reference electrode) along with the cathodic contraction at -800 mV in CSV. The film obtained from the same lot, however, showed cathodic contraction and anodic expansion only by changing the oxidative potential from 600 mV to - 100 mV. This phase inversion indicates that not only the polymerization electrolyte but also the redox potential determines the (de)insertion of ions in the PPyPPS film. Contractive electrochemical creeping was only observed in PPyPPS film in chloride salt electrolytes, indicating that the cation insertion induces the deinsertion of initial-dopant anion from the film.