Electrografting Polyaniline on Carbon through the Electroreduction of Diazonium Salts and the Electrochemical Polymerization of Aniline

Electroreduction of diazonium salts and electropolymerization of conductive polymers are two widely used techniques for producing modified electrodes. In this work, these two techniques are combined in order to functionalize glassy carbon electrodes. In a first step, a thin layer of diphenyl amine (DPA) is grafted through the electrochemical reduction of the 4-aminodiphenylamine (ADPA) diazonium salt. The DPA grafted layer has been studied using XPS and SECM. It appears to act as a switch giving diode-like behavior for probes with a redox potential below 0.4 V. As a consequence, aniline oxidation remains possible on this substrate, and polyaniline (PANI) can easily be deposited on the DPA-modified electrodes. The PANI films generated on such modified electrodes show electrochemical behavior similar to that of PANI electrodeposited on bare carbon electrodes but exhibit better chemical stability and high resistance to aggressive environments, that is, high temperatures and ultrasonic etching. Such results, associated with the scanning electrochemical microscopy response of the modified electrodes, strongly suggest that PANI is grafted covalently on the DPA layer. From a fundamental point of view, the results show that surface graft polymerization can be extended to surface graft electropolymerization. From a practical point of view, the method described in this work is a simple and efficient process for improving the stability of an electrodeposited conducting polymer, that is, polyaniline, on a carbon substrate and could be of considerable importance in the synthesis of PANI/carbon nanotube composites.