High performance electrochemical supercapacitor from electrochemically synthesized nanostructured polyaniline Vinay Gupta a,b, ⁎ , Norio Miura a a Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga-shi, Fukuoka 816-8580, Japan b Japan Science and Technology Agency, Saitama, 332-0012, Japan Received 12 September 2005; accepted 15 November 2005 Available online 7 December 2005 Abstract Polyaniline nanowires were electrochemically deposited on stainless steel electrode at the potential of 0.75 V vs. SCE and characterized by cyclic voltammetry in 1 M H 2 SO 4 electrolyte for supercapacitive properties. A high specific capacitance of 775 F g - 1 was obtained at the sweep rate of 10 mV s - 1 . A long-term cyclic stability of the polyaniline nanowires demonstrated its implications for the high performance supercapacitors. © 2005 Elsevier B.V. All rights reserved. Keywords: Polyaniline; Deposition; Nanowire; Cyclic voltammetry; Supercapacitor Electrochemical supercapacitors are the charge-storage devices having high power density and long cyclic life [1–5]. The increasing pollution due to electrical vehicles and explosive growth of portable electronic devices have pushed the development of high performance supercapacitors as the urgent requirement. Supercapacitors store energy in the form of charge at the electrode/electrolyte interface and can be divided into two categories: (i) redox supercapacitors, in which the pseudocapa- citance arises from faradic reactions occurring at the electrode interface and (ii) electric double layer capacitors (EDLCs), in which the capacitance arises from the charge separation at the electrode/electrolyte interface. The main materials that have been studied for the super- capacitor electrode are (i) carbons, (ii) metal oxides and (iii) polymers. The polymers are considered the most promising material in the supercapacitors. Among the polymers, such as polymethyl methacrylate (PMMA) [6], p-phenylenevinylene (PPV) [7], polypyrrole (PPy) [8–10] and polyaniline (PANI) [11–13], polyaniline is considered the most promising material in the supercapacitors due to its high capacitive characteristics, low cost and ease of synthesis. The materials in the nano-size form with high surface area and high porosity give the best performances as the electrode materials for supercapacitors because of their distinctive characteristics of conducting pathways, surface interactions, and nanoscale dimensions. Therefore, the synthesis and the capacitive characterization of the high surface area nanomater- ials such as nanotubes, nanowires, [14–16] etc. have been carried out extensively in the past few years. Consequently, different indirect methods were used to synthesized nanosized polyaniline, such as template synthesis [17], self-assembly [18], emulsions [19] and interfacial polymerization [20]. However, such methods require relatively large amounts of surfactants, which are rather tedious to recycle after polymerization, and it is difficult to attach nanosized polyaniline onto a substrate without involving large contact resistance. Therefore nanosized polyani- line synthesized by such methods is not suitable for super- capacitors applications. The best way is direct deposition of the nanostructured polyaniline onto a substrate electrode. In the present work, for the first time, we have performed cyclic votammetric measurements of the polyaniline nanowires electrochemically deposited directly on the stainless steel electrode for supercapacitor application. Materials Letters 60 (2006) 1466 – 1469 www.elsevier.com/locate/matlet ⁎ Corresponding author. KASTEC, Kyushu University, Kasuga-shi, Fukuoka 816-8580, Japan. Tel./fax: +81 92 583 7886. E-mail address: drvinaygupta@netscape.net (V. Gupta). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.11.047