Effect of fluoride ion on the electrochemical formation of polypyrrole and the role of point of zero charge on the polymerisation

Abstract

The unusual effect of fluoride ion in the oxidation of pyrrole in trifluroacetic acid (TFA) at Pt and indium in oxide glass electrode (ITO) is reported. The oxidation produces a redox couple with <i>E</i>_pa = 0.40 V and <i>E</i>_pc = - 0.30 V at both the electrode surfaces. At ITO glass electrode the oxidation is characterised by increasing peak currents in cyclic voltammetry upon repetitive cycling. The formation of polypyrrole has been confirmed by <i>in situ</i> spectro electrochemical studies which show a characteristic absorption beyond 500 nm. The presence of fluoride ion in the medium inhibits the formation of polypyrrole at Pt electrode. However, experiments conducted with Au sputtered on microscopic glass plate as the working electrode show the formation of polypyrrole film in the presence of fluoride ion. These results have been interpreted on the basis of specific adsorption of fluoride ion on the Pt electrode (point of zero charge=0.15 V versus NHE).