OVEROXIDATION OF POLYPYRROLE IN PROPYLENE CARBONATE - AN INSITU FTIR STUDY

Irreversible oxidation of thin polypyrrole layers was studied in 0.5M LiClO4/propylene carbonate (PC) by the subtractively normalized interfacial Fourier transform infrared spectroscopy method. For comparison, some measurements were performed in acetonitrile instead of PC. In PC, carbon dioxide, a product of anodic oxidation of propylene carbonate, reacts with trace water present in the electrolyte to give H2CO3. Nucleophilic HCO3- and OH- species then attack the doped polypyrrole chains leaving a yellow, nonconjugated, and electrochemically rather inactive overoxidized polymer. The rate of overoxidation during polymer cycling in the 2.0-4.0 V (vs. Li/Li+) potential range depends strongly on the concentration of water in the electrolyte.