Influence of the Cation Nature of the Sulphate Salt on the Electrochemical Synthesis of Sulfate-Doped Polypyrrole

In this work, polypyrrole films were electrosynthesized from aqueous media onto a graphite-epoxy resin composite electrode (GCE) using sulphate ions as dopant. Potentiostatic electrosynthesis studies were done using different salts as SO4-2 source, namely: Na2SO4, Li2SO4, (NH4)2SO4 and K2SO4. The potentiometric response of the diverse Ppy-SO4-2 films was evaluated by means of calibration plots; according to the slope sign the behavior of the different films can be classified in three responses: anionic, cationic and anionic-cationic. Such behaviors were observed for all synthesized films, independently of the sulphate salt used. When analyzing the current transients obtained for the different salts, similarities were found for those with the same potentiometric behavior, but significant differences were observed when comparing transients of different potentiometric responses. From the analysis of the experimental current transients it was determined that the nature of the cation of the sulphate salt influences the number density of active sites on the electrode surface where the Ppy-SO4-2 is deposited. Moreover, the kind of Ppy-SO4-2 potentiometric response also depends on the type of cation used during the polymer electrochemical synthesis. According to the results obtained, some boundaries for the potentiostatic synthesis parameters are suggested to induce a specific potentiometric response.