Polyaniline/carbon nanotube composite films electrosynthesis through diazonium salts electroreduction and electrochemical polymerization † Luisa Pilan,* Matei Raicopol, Alina Pruna and Viorel Branzoi In this work, we combine two widely used techniques to produce modified electrodes, that is, the electroreduction of diazonium salts and the electropolymerization of conductive polymers in order to obtain polyaniline (PANI)/carbon nanotube (CNTs) composites. Thus, in a first step, a CNTs electrode was functionalized with 4-nitrophenyl group by electrochemical reduction of 4-nitrobenzenediazonium salt in nonaqueous media. Then, the nitro group was reduced elec- trochemically to amine functionality. Cyclic voltammetry and electrochemical impedance spectroscopy were used to trace the reactions in each step. The PANI film can easily be grafted onto the surface of such obtained aminophenyl-modified CNTs electrodes. The PANI/CNTs films generated by this strategy show electrochemical behavior similar to that of PANI simply electrodeposited on CNTs electrodes, but exhibit significantly improved stability and higher capacitance values. Copyright © 2012 John Wiley & Sons, Ltd. Keywords: diazonium salts; polyaniline; carbon nanotube; composite films; electrosynthesis Introduction Since the discovery of carbon nanotubes (CNTs), extensive research in the fields of applied physics, chemistry, materials science, and engineering has rapidly emerged. [1] Owing to their outstanding mechanical properties, good electronic conductivity, nanometer size, and high-accessible surface area, CNTs can be used to prepare the multi-functional composites with excellent electronic and mechanical properties. On the other hand, conducting polymers (CPs) such as polypyrrole, polyaniline (PANI), and polythiophene have attracted much attention due to their unusual electronic and optical properties with potential applications in solar cells, capacitors, gas and ion sensors, and elec- tronic devices. Due to their poor mechanical properties, CPs usually are mixed with other polymers, though this fact has a negative impact in the conductivity, since the charge transfer path is broken after the addition of the macromolecular chains. [2] Over the past decade, tremendous efforts have been made to prepare CP/CNT composites with an aim to synergistically combine the merits of each individual component. [3] The strong interaction between the highly delocalized p-electrons of CNTs and the p-electrons correlated with the lattice of the polymer skeleton favors the electron/hole transfer between CNTs and CPs. [4,5] Among various CPs, PANI has potential uses in synthesiz- ing CP/CNT composites owing to its environmental stability, good processability, and reversible control of conductivity both by protonation and charge-transfer doping. [6] CP/CNT composites can be obtained using three major syn- thetic methods: electrodeposition of the CP onto a preformed CNT-modified electrode, [7] chemical synthesis, [8] and electro- co-deposition of the CNTs and CP onto a bare electrode. [9] Lack of strong interfacial bonding between CNTs and the polymer invalidates load transfer, resulting in tube pullout and subsequent catastrophic failure. [10] Various strategies have been reported in the literature to enhance the interaction between the CP matrix and the nanotubes. [11–13] Thus, functionalization represents an effec- tive way to improve interfacial bonding. Noncovalent approaches, such as wrapping, [12] are capable of preserving intrinsic properties when improving exfoliation and interfacial bonding. However, it was reported wrapping works poorly for small-diameter tubes. [13] The covalent methods of functionalization through grafting specific functional groups onto the surface of the CNTs provide strong covalent bond between tubes and polymer so that load-transfer capability is significantly enhanced. In this work, we report a simple and efficient approach for electrochemical preparation of nanocomposite films of PANI and single-walled CNTs (SWCNTs) with improved stability and electrochemical properties. For this, we combine two widely used techniques to produce modified electrodes, that is, the electrore- duction of diazonium salts and the electropolymerization of conductive polymers. Thus, in a first step, a CNTs electrode was functionalized with 4-nitrophenyl group by electrochemical reduction of 4-nitrobenzenediazonium salt in nonaqueous media. Then, the nitro group was reduced electrochemically to amine functionality. [14,15] Cyclic voltammetry (CV) and electrochemical * Correspondence to: Luisa Pilan, University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, 1 Polizu, 010737 Bucharest, Romania. E-mail: luisa_pilan@yahoo.com † Paper published as part of the ECASIA 2011 special issue. University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, 1 Polizu, 010737, Bucharest, Romania Surf. Interface Anal. (2012) Copyright © 2012 John Wiley & Sons, Ltd. ECASIA special issue paper Received: 23 August 2011 Revised: 20 January 2012 Accepted: 7 February 2012 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/sia.4920