Evaluation of corrosion resistance of polypyrrole/functionalized multi-walled carbon nanotubes composite coatings on 60Cu–40Zn brass alloy

•PPy/MWCNT and PPy/MWCNT-COO− films were electropolymerized on brass.•Strongly adherent and smooth nanocomposite film was obtained.•MWCNT improves both alloy passivation and coating cationic permselectivity.•PPy/MWCNT-COO− provided higher corrosion resistance than PPy/MWCNT alone.

Polypyrrole/multi-walled carbon nanotubes (PPy/MWCNT) and its carboxylic functionalized (PPy/MWCNT-COO−) composite films were successfully electropolymerized by cyclic voltammetry as protective coating against corrosion on 60Cu–40Zn brass alloy surface. It yielded to strongly adherent and smooth nanocomposite films. Kinetics of the corrosion protection was investigated in 3.5 wt% NaCl solutions by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The results showed that the presence of MWCNT in PPy coat considerably reduces the corrosion rate of 60Cu–40Zn brass alloy. The enhanced inhibition is most likely due to interaction between MWCNT and PPy. This in turn, improves the alloy passivation improvement and alters the permselectivity of the coating from anionic selectivity to the cationic selectivity. Moreover, PPy/MWCNT-COO− functionalized nanocomposite provided higher corrosion resistance coating than PPy/MWCNT alone.