Kinetics and efficiency of aqueous electropolymerization of pyrrole onto low-carbon steel

Abstract

The effect of process parameters on the conversion, P, and current efficiency, η, for the aqueous electropolymerization of pyrrole on low-carbon steel has been investigated. The amount of polypyrrole coatings formed on steel, Wp, increased with the charge passed, Q, and the initial pyrrole concentration [M], but was unaffected by the electrolyte concentration. The conversion of pyrrole into polypyrrole, P = WP/WM, increased with electropolymerization time, and the applied current, and decreased with the initial monomer concentration. The oxalic acid concentration had no significant effect on conversion. The current efficiency for the electropolymerization of pyrrole performed by using high applied current, I(I ≥ 40 mA), and high pyrrole concentration, [M] ≥ 0.5M, rose to its highest value at short polymerization times, t < 300 sec. It then decreased and leveled off at longer times, t ≥ 1,000 sec. At low applied current, I ≤ 20 mA, and low pyrrole concentration, [M] ≤ 0.25M, the current efficiency increased gradually with increased reaction parameters ([M], I, and t) and reached a maximum value at t = 1,000 sec. A retrogression of the current efficiency occurred at t ≥ 1,000 sec, for the reaction performed by using applied current of 10 mA. Overall, the current efficiency varied between 39 and 130%, with the higher values occurring at high pyrrole concentration and high applied current. The current efficiency was determined from the ratio of the experimental and theoretical electrochemical equivalents for polypyrrole. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:617–624, 1997