Interconnected polyaniline clusters constructed from nanowires: Confined polymerization and electrochemical properties

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eshan Qiu, Chang Yu, and Zongbin Zhaob) Carbon Research Laboratory, School of Chemical Engineering, State Key Lab of Fine Chemicals, Dalian University of Technology, Dalian 116023, China (Received 10 March 2014; accepted 25 August 2014)

By using microemulsion-mediated solvothermal method in the presence of camphorsulfonic acid as a dopant, self-aggregated polyaniline (PANI) nanowires were synthesized and further organized into three-dimensional cluster-connected networks. So-formed PANI exhibited a hierarchically porous structure, which was significantly different from those obtained by conventional chemical oxidation method, hydrothermal method, and other reported methods. Compared with nanofibers presented in this study, the nanowires in the clusters had a great decrease in diameter from ;60 to ;15 nm due to the space-confined polymerization. In addition, the size of the clusters could be easily adjusted by altering the dopant/monomer molar ratio. A probable assembly mechanism for such an interesting morphology was proposed. Used as an electrode material, PANI clusters showed high specific capacitances (510 and 368 F g1 at 0.5 and 2 A g1, respectively) and improved cycling stability (66% capacitance retention over 1000 cycles) as compared to PANI fibers and particles obtained by other methods, which may be related to its unique morphology and high doping level. I. INTRODUCTION

The development of clean and sustainable energy storage and conversion systems is crucial to solve energy and environment issues around the globe.1 Supercapacitor as a typical device has received great attention since some attractive properties such as high power density, fast charge/discharge (CD) rate, and long cycle life, allow them expansive applications in portable electronic devices and hybrid electric vehicles.2,3 So, the controllable fabrication of ideal electrodes with low diffusion resistance of electrolytes, high-rate transportation, and high accessible active area, necessarily becomes a research focus as well as a technological challenge.4 Polyaniline (PANI) based on redox pseudocapacitive charge storage mechanism is considered as one of the leading electrode materials because of its versatile and economic preparation method, nontoxic property, high environmental stability, relatively high capacitance, and reversible doping/dedoping process.5–7 Currently, various PANI micro/nanostructures including wires/fibers/tubes/ rods/hollow capsules/flowers/tetragonal stars/belts/sheets depending on synthetic means have been reported.8–18 For

Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2014.263 2408

J. Mater. Res., Vol. 29, No. 20, Oct 28, 2014

Downloaded: 11 Mar 2015

instance, cyclodextrin-templated “hairy urchin”-shaped PANI was synthesized by microemulsion polymerization.19 By varying the monomer concentration and the feeding ratio of dichloroacetic acid to aniline, the evolution of PANI shape from one-dimensional (1D) nanotubes to