Electrochemical polymerization of para-chloroaniline as highly redox-active poly(para-chloroaniline) on graphitized mesoporous carbon surface

Owing to the high demand of conducting molecular systems for various electronics and technological applications, development of new polyaniline (PANI)/carbon nanomaterial is a continued research interest in cross-disciplinary area of material chemistry. In the literature, for the preparation of PANI/carbon nanomaterial composite electrode systems ex-situ preparation method, in which, chemical oxidation of aniline in presence of carbon nanomaterial, followed by modification on solid substrate has been widely adopted. In this work, a systematic study has been carried out for in-situ electrochemical polymerization of 4-chloroaniline and other substituted aniline monomers to respective PANI on graphitized mesoporous carbon (GMC), that show porous structure and enormous sp2 sites to aniline and PANI for π-π interaction, unusually in neutral pH condition. The new [email protected] modified electrode showed a highly redox active peak at Eo' = 0.12 V vs Ag/AgCl in pH 7 phosphate buffer solution. No such behaviour was noticed when an unmodified glassy carbon was used as working electrode for the polymerization in the above mentioned condition. The redox peak is found to be stable, surface-confined and Nernstian type of proton-coupled electron-transfer in nature. Based on the physicochemical characterization techniques using Raman, IR, X-Ray photoelectron-spectroscopy, scanning electron-microscope and scanning electrochemical microscope (SECM) instruments and electrochemical studies with several ortho, para and meta substituted aniline monomers, mechanism for the in-situ polymerization has been revealed that 4-chloroaniline monomer has undergone a surface-confined electrochemical oxidation reaction with involvement of aniline(4-Cl)-cation radical species, anti-orientation of the monomer (that exist in solution phase), head-to-tail collision (C-N bonding), ejection of the para-substituents as Cl- and Cl•, partial chlorination and PANI(4-Cl) formation mechanism. Such a PANI(4-Cl) film showed a wave-like 2D molecular film structure with enhanced redox and electrical property over the conventional PANI system.