Electrochemical synthesis of polypyrrole nanowires

Abstract

Nanomaterials have wide-ranging applications in a variety of areas, including chemistry, physics, electronics, optics, materials science, and the biomedical sciences. Potential applications in several fields such as micro-devices, catalysis, sensors, and artificial organs are envisaged. Synthetic methods used for preparation of one-dimensional nanomaterials consisted of template, catalysis, surfactant-assistant, and self-assembly systems. Electronically conductive polymers such as polypyrrole (Ppy) have been investigated for the applications in second batteries [1], sensors and actuators [2, 3], and optical devices [4]. Many studies have been made on morphologies, nucleation and growth mechanisms of Ppy [5, 6]. Ppy nanowires and nanotubes are mainly prepared by template methods [7–16]. It is noteworthy that the nanofibers and nanotubules synthesized by the “template method” have shown higher conductivity and strength over conventional bulk-synthesized forms [17, 18]. Ppy nanowires can also be obtained at the edge of lipid-tubules [19], and at the steps and pits defects of highly-ordered-pyrolytic-Graphite (HOPG) [20]. Ppy nanowires are obtained at the HOPG steps at under-potential, with diameters no greater than 10 nm; its growth pattern is two-dimensional type. In the present work, we developed a new method to synthesize the Ppy nanowires by electrochemical polymerization in the presence of polyanion(poly(maleic acid-co-vinyl pyrrolidone)). The electropolymerization was conducted in a one-compartment cell using a saturated calomel electrode (SCE) as the reference electrode, a platinum coil as counter electrode, and a graphite rod with diameter of 8 mm as working electrode. The experiments were performed on TD 73000 Electrochemical System controlled by a computer. The scanning electron microscope (SEM) photographs of Ppy were obtained using Philips XL30. The solution used in the experiments contained 20 mg poly(maleic acid-co-vinyl pyrrolidone), 60 mg lithium perchlorate and 50 × 10−9 m3 pyrrole in 5 × 10−6 m3 aqueous solution. The Ppy nanowires can be electrogenerated on the graphite electrode by either a potential step experiment or cyclic voltammetry. Fig. 1 shows Ppy nanowires prepared with different charge consumption during electropolymerization.