The effect of pH on the electrochemical polymerisation of pyrrole on aluminium

Attempts to obtain polypyrrole films on aluminium were made by means of cyclic voltammetry, chronoamperometry and chronopotentiometry in nitrate solutions containing pyrrole in the range of pH 4–13. It was found that the solution with pH 12 was the only one that allowed electropolymerisation. The oxide layer formed at this pH was able to inhibit partially the dissolution of the metal without inhibiting the oxidation of the monomer. The passive film formed seemed to be less protective than that obtained in 0.1 M HNO3. The best quality films at pH 12 were produced potentiostatically. Nucleation of the polymer was initiated at defects in the passive film. A competition between the process of metal passivation and Py electropolymerisation resulted in highly localised deposits of the polymer under galvanostatic conditions. The deposited coatings were characterised electrochemically. The influence of Al oxide characteristics and nitrate concentration on the electropolymerisation process is discussed.