Polypyrrole electrogeneration from a nucleophilic solvent (DMF)

Abstract

In spite of difficulties pointed out in the literature thick polypyrrole film can be obtained on platinum from NaClO 4-DMF solutions. The polymerization rate increases at constant potential when the potential increases from 900 to 2400 mV(SCE) and the rate decreases at higher anodic potentials. The productivity of the consumed charge, as mg of polymer generated per mC of charge, decreases at increasing potentials. When temperature decreases the polymerization rate increases pointing to a high activation energy of parallel passivation reactions during polymerization. From the ‘ex situ’ microgravimetric method the following empirical kinetics was obtained: Rp = k[pyrrole] 0.5[ClO 4 −] 1.3. The formation of polymeric films was controlled by cyclic voltammetry in the background electrolyte. From the stored charge and the polymer weight the stored charge per mg of electrogenerated polymer for each film could be estimated. When the concentration of ClO 4 − ions increases both the polymerization rate and the capacity to store electrical charge in films increases, which indicates that ClO 4 − ions act as retarding agents of passivation processes during polymerization. In general, the ability to store electrical charge in polypyrrole electrogenerated in different solvents decreases when the donor ability of the solvent increases. At higher temperatures a faster nucleophilic attack of the solvent to the positively charged polymer is proposed to occur, promoting an increasing passivity of the film. The productivity of the polymerization charge decreases at increasing temperatures and increases at increasing concentrations of electrolyte and passes through a maximum when the concentrations of monomer increase.