Increased Redox-Reaction Rate of Quinhydrone at N-Substituted Polypyrrole Film Electrodes

A poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium] perchlorate-coated glassy carbon electrode noticeably decreased the charge-transfer resistance (Rt) of quinhydrone relative to a naked glassy carbon electrode. The redox species was not concentrated into a polymer film; this result differs markedly from the very good absorption of anthraquinonesulfonates and indigosulfonates by a polymer film. The dependence of Rt and the interfacial capacitance on the film thickness implies that the charge-transfer process occurs at the film-solution interface, because the polymer film is appreciably electronically conductive at positive potentials. Because of a change in the film conductivities with the potential, the polymer-coated electrode increased the anodic peak current of quinhydrone by three times, but decreased its cathodic peak current by two fifths, relative to that of a naked electrode. Although the decrease in Rt at a polymer-film electrode is somewhat ascribed to an increasing area, which is due to a porous film surface, the electrocatalytic effect of the polymer film can be attributed to an increasing standard rate constant of the charge-transfer process; this increase may be due to the adsorption of quinhydrone on the polymer surface