Highly Enhanced Anion Doping-Undoping Process at the Polypyrrole Electrode of Regulated Morphology Prepared with the Aid of Insulating NBR Film

A polypyrrole (PPy) film grown with the aid of a precoated nitrile rubber (NBR) by an electropolymerization method was found to show a highly enhanced anion doping-undoping process because of its oriented grown structure. In the procedure of the preparation of this special electrode (Pt/NBR/PPy), a NBR film, originally insulating and soluble in electrolyte solution of acetonitrile(AN)/LiC1O₄, played the role of a host polymer regulating the growth of PPy film in the direction perpendicular to the substrate. The guest polymer of PPy film grew through the fine channels etched by the penetration of the electrolyte into the NBR film during electropolymerization. The host polymer of NBR film was subsequently removed in order to leave the backbones of the grown PPy film. The basic electrode kinetics of the thus prepared Pt/NBR/PPy electrode were investigated by contrasting them with a PPy film grown in a straight forward way on Pt substrate (Pt/PPy). Potential step and ac impedance measurements for these electrodes evidenced that a Pt/NBR/PPy electrode showed faster anion doping process than a Pt/PPy electrode. Inspection by SEM revealed that a PPy film grown directly on Pt substrate showed a rather compact structure. In contrast, a PPy film formed with the aid of NBR polymer had rough, porous, and somewhat perpendicularly oriented structure, indicative of the special history of the formation procedure. These micrographs gave scientific support to the evidence of an advantageous electrochemical property of Pt/NBR/PPy electrode when utilizing it for a cathode active material of a rechargeable lithium battery.