Degradation behavior of free-standing polypyrrole films in NaOH solution

Free-standing polypyrrole (PPy) films hold promising potential in flexible energy storage devices, actuators, and artificial muscles, but they are limited by service failure. In this work, free-standing PPy/p-toluenesulfonate (PPy/pTS) films with different thickness (1.8 and 4.2 mu m) were prepared, and their degradation behavior in aerated and de-aerated 0.5 M NaOH was investigated to make clear the changes of chemical and electrochemical degradation processes on free-standing PPy films. The degradation of electrochemical activity of the free-standing PPy film leads to an obvious increase in its internal resistance and shows similar kinetics as the PPy film with a Pt substrate, i.e. one degradation stage and its rate follows first-order kinetics. The degradation rate constant (k) in aerated NaOH increases largely owing to the existence of the dominant electrochemical degradation process. The k value of the thick film (4.2 mu m) decreases obviously resulting from a more ordered and compact structure, which limits ion diffusion in the polymer matrix so as to greatly inhibit the chemical degradation process. The free-standing PPy film shows lower electrochemical activity and much larger k values compared with the PPy film with a Pt substrate under the same condition. The mechanisms involved were discussed. (C) 2018 Elsevier Ltd. All rights reserved.