THE ION-EXCHANGE MECHANISM OF POLYPYRROLE IN PROPYLENE CARBONATE AND DIMETHYLSULFITE BASED ELECTROLYTES - AN INSITU PROBE BEAM DEFLECTION STUDY

In situ probe beam deflection (PBD) along with cyclic voltammograms have been used to monitor the ion exchange between polymer film and bulk electrolyte during the redox reactions of polypyrrole (PPy) in propylene carbonate (PC) and dimethylsulfite (DMSU) based electrolytes containing LiClO4. During the reversible oxidation and reduction of PPy in PC the PBD results confirmed that anion exchange takes place in the faradaic as well as in the pseudocapacitive part of the cyclic voltammogram. In the potential region where significant irreversible changes occur (E > 4 V vs. Li/Li+), the negative sign of the beam deflection signal during the positive scan shows expulsion of species; previous in situ Fourier transform infrared spectroscopic (FTIRS) results showed expulsion of anion-containing species from the polymer. In DMSU based electrolyte, however, Li+ insertion/expulsion takes place during the reversible cycling of polypyrrole in the potential interval from 2.0 to 4.0 vs. Li/Li+. In the latter electrolyte, up to one electron per pyrrole ring can be transferred reversibly which leads to a charge density of about 160 Ah/kg.