ELECTROCHEMICAL POLYMERIZATION OF PYRROLE IN AQUEOUS BUFFER SOLUTIONS

Studies of the electrochemical polymerization of pyrrole on indium tin oxide coated glass and platinum electrodes in several aqueous buffer solutions are presented. It was found that the polymerization proceeded smoothly in Kolthoff buffers of pH 2-3.5, leading to conducting polypyrrole (PPy) films. In the buffers of pH 4-5, films of non-uniform thickness were produced with a structure rather different from that of conducting PPy. No film formation occurred on the bulk surfaces of the working electrodes in buffers of pH greater-than-or-equal-to 7. In other buffer systems the suppression of pyrrole polymerization was also observed when the buffer pH was higher than 5-7. The critical pH values depended on the supporting electrolytes, buffer species, and the working electrode substrates. However, scanning electron microscopy images and the electroactivity study of the platinum electrode indicated that a thin layer deposit had been produced on the platinum surfaces, though the bulk electropolymerization was hindered. The causes for the suppression are considered to be (1) the formation of a thin layer of electro-inactive deposit at the initial stage of electrolysis, (2) the removal of H+ ions by the buffers, and (3) nucleophiles present in the solution.