KINETICS AND EFFICIENCY OF AQUEOUS ELECTROPOLYMERIZATION OF PYRROLE ONTO LOW-CARBON STEEL

The effect of process parameters on the conversion, P, and current eff iciency, eta, for the aqueous electropolymerization of pyrrole on low- carbon steel has been investigated. The amount of polypyrrole coatings formed on steel, W-p, increased with the charge passed, Q, and the in itial pyrrole concentration [M], but was unaffected by the electrolyte concentration. The conversion of pyrrole into polypyrrole, P = W-P/W- M 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 eff iciency for the electropolymerization of pyrrole performed by using hi gh applied current, I(I greater than or equal to 40 mA), and high pyrr ole concentration, [M] greater than or equal to 0.5 M, rose to its hig hest value at short polymerization times, t < 300 sec. It then decreas ed and leveled off at longer times, t greater than or equal to 1,000 s ec. At low applied current, I less than or equal to 20 mA, and low pyr role concentration, [M] less than or equal to 0.25 M, the current effi ciency 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 greater than or equal to 1,000 sec, for the reaction performed by using applied current of 10 mA. Ov erall, the current efficiency varied between 39 and 130%, with the hig her values occurring at high pyrrole concentration and high applied cu rrent. The current efficiency was determined from the ratio of the exp erimental and theoretical electrochemical equivalents for polypyrrole. (C) 1997 John Wiley & Sons, Inc.