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The role of H+ ions in the electrochemical polymerization of pyrrole

Pyrrole was found to polymerize electrochemically in a smooth and facile way when the immediate vincinity of the anode is at a pH of 3 ([H+] = 10−3 mol/dm3). The polymerization is inhibited by the presence of a H+ scavenger, di-tert-butylpyridine. Polymerization of pyrrole in a buffered solution of pH 4 gives a polypyrrole (PPy) film of slightly different chemical structure from that obtained in a buffered solution of pH 3, as shown by their IR spectra. No polymerization takes place in the buffered solution at pH > 7. These facts show the important role of H+ ions played in the electrochemical polymerization of pyrrole. Pyrrole might go through a protonated structure before it transfers an electron to the electrode, to form a cation radical which starts the polymerization. A new mechanism of polymerization is proposed in conformity with observed facts about the structure of PPy.