Electrochemical synthesis of polypyrrole: Influence of current density on structure

Abstract

A systematic study of the influence of the current density during electropolymerization on the properties of polypyrrole has been carried out. 0.5 M LiClO 4 in propylene carbonate has been used as electrolyte. The current density was varied between 6.4 μA/cm 2 and 3.84 mA/cm 2. Two types of polypyrrole films can be identified: low current (i ≤ 300 μA/cm 2), and high current forms (i ≥ 500 μA/cm 2). The limiting modifications are obtained when using i ≤ 60 and i ≥ 2000 μA/cm 2, respectively. The low current density form shows detailed structure with narrow peaks in cyclic voltammograms, and has a high degree of conjugation, as seen from the low value of the π−π transition (2.83 eV). This form is able to accomodate up to 0.37 ClO 4 − ions per pyrrole unit up to 3.5 V vs Li compared to only 0.22 for the high current form. Since PPy films have often been formed at current densities from 0.5 to several mA/cm 2, much previous work has been based on forms approaching the high current modification to varying degrees. This explains part of the discrepancies in the literature. As the low current form seems to be closer to the intrinsic properties of pure polypyrrole, it is to be preferred as a point of reference for investigating the effects of changing conditions on properties.