Electropolymerization of polypyrrole films on stainless steel substrates for electrodes of electrochemical supercapacitors

Polypyrrole (PPY) films were obtained on stainless steel substrates by anodic electropolymerization using 2,6-naphthalenedisulfonic acid disodium salt (NSA) and chromotropic acid disodium salt (CHR) as anionic dopants. The deposition potential of PPY from the solutions containing CHR was ∼0.4 V lower than that for NSA. Adherent PPY films were obtained from pyrrole solutions containing CHR. The comparison of the experimental data for CHR, containing OH groups bonded to the aromatic rings, and NSA without OH groups showed that the interaction of OH groups with metal atoms at the substrate surface promoted the formation of adherent films. The deposition was performed galvanostatically or potentiodynamically and the deposition yield was studied. The PPY films showed capacitive behaviour in the 0.5 M Na2SO4 electrolyte. The specific capacitance (SC) increased with increasing pyrrole and CHR concentration in the solutions used for deposition. Electron microscopy investigations showed that the increase in SC with increasing CHR concentration can be attributed to decreasing particle size and increasing film porosity. The highest SC of 343 F g−1 was observed at 2 mV s−1 for the films prepared from the solutions containing 150 mM pyrrole and 50 mM CHR. The SC decreased with increasing scan rate. The SC decrease in thick films was attributed to increasing electrochemical impedance, which was analysed at different frequencies using an equivalent circuit. The cycling stability of the films was investigated. The PPY films prepared on stainless steel substrates by electropolymerization are promising electrode materials for electrochemical supercapacitors.

► Adherent polypyrrole films were obtained on stainless steel by electropolymerization.
► Chromotropic acid promoted film adhesion and electropolymerization.
► The films showed specific capacitance of 343 F g−1 in 0.5 M Na2SO4 electrolyte.
► The polypyrrole films can be used for electrochemical supercapacitors.