Potentiodynamic deposition of polyaniline on non-platinum metals and characterization

Polyaniline (PANI) was potentiodynamically deposited on stainless steel (SS), Ni, Ti, Al and Pb electrodes from aqueous solutions of $NaClO_4$, oxalic acid and $H_2SO_4$ of different concentrations. Platinum was also used as a substrate for the purpose of comparison. Although, the non-platinum metals showed reactivity in the electrolytes, the adsorption of aniline monomer occurred leading to initiation and growth of PANI during repeated potential sweeps. The nature of voltammograms of the non-platinum metals during PANI deposition differed from that of the Pt electrode. Subsequent to potentiodynamic deposition, the electrodes were studied for their electrochemical activity in $0.5 M H_2SO_4$ without and with dissolved redox species. On all metals, the PANI exhibited the potentiodynamic peak at about 0.2 V corresponding to transition from leucoemaraldine (LE) state to emeraldine (EM) state at low scan rates. However, this peak disappeared on repetition of potential scan and also at high scan rates. The PANI deposited on non-platinum metals showed response to dissolved redox species, viz. hydroquinone/quinone, ferrous/ferric, ferrocyanide/ferricyanide, as reflected in the potentiodynamic and ac impedance measurements. However, the peak potential separation of cyclic voltammograms was very large