Electrosynthesis of polyindole-carboxylic acids on stainless steel and their corrosion protection at different temperatures in acidic solution

Poly (indole-5-carboxylic acid) (5-PICA), Poly (indole-6-carboxylic acid) (6-PICA), and Poly (indole-7-carboxylic acid) (7-PICA) were electrowinning onto AISI304 stainless steel by cyclic voltammetry. They were characterized structurally and morphologically by IR spectroscopy and scanning electron microscopy (SEM). In addition, the study about corrosion protection was carried out using linear scanning voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in 0.5 mol·L⁻¹ H₂SO₄ at temperatures of 20 °C and 45 °C. The results showed a close relationship between the morphology of the polymer and the carboxylic group (–COOH) position, which also presented a spatial arrangement according to its branching. Furthermore, it directly modified its hydrophobicity, influencing the anticorrosive protection of AISI304 stainless steel. It provides a corrosion potential between 0.198 and 0.402 V, which is more positive than unprotected steel. Finally, the study revealed better protection at low temperatures, decreasing at 45 °C.