The possibility of incorporating 4-(pyrrole-1-yl) benzoic acid, (PyBA), and heteropolyacids (SiMo12) during the electrodeposition of poly (3,4-ethylenedioxythiophene), PEDOT, is demonstrated in the paper. The formed novel composite material was applied on the electrode surface as a moderately thin (ca. 0.9-1 mu m thick) PEDOT/PyBA/SiMo12 coating. The physicochemical identity of our composite coating was established with the use of electrochemical, spectroscopic, and microscopic techniques. The fact that carboxylate-containing PyBA units link with positively charged and PEDOT structures tend to improve the overall stability and adherence of composite coatings to glassy carbon and stainless steel. The PEDOT/PyBA composite serves as a stable host matrix for large negatively charged silicium hetero-polymolybdates inorganic species. Consequently, due to the formation of denser polymeric structures and due to the existence of electrostatic repulsion effects, the large polyanion-containing composite coatings are capable of blocking the access of smaller pitting-causing anions (chlorides) to the surface of stainless steel. (C) 2014 Elsevier B.V. All rights reserved.