Conducting polymers as electrode materials in supercapacitors Marina Mastragostino a, * , Catia Arbizzani b , Francesca Soavi a a Radiochimiche e Metallurgiche, Unita’ Complessa di Istituti, Scienze Chimiche, Radiochimiche e Metallurgiche, University of Bologna, via San Donato 15, I-40127 Bologna, Italy b Department of Chemistry ‘‘G. Ciamician’’, University of Bologna, via Selmi 2, I-40126 Bologna, Italy Abstract This paper summarizes the performance data of conventional and especially designed thiophene-based conducting polymers for use as positive and negative electrodes in n/p type supercapacitors. Performance data of polymer composite electrodes are also compared with those of high surface area carbon-based composite electrodes. On the basis of capacity, capacitance and electrode charging resistance data, we selected the best electrode materials, and assembled and tested galvanostatic charge – discharge cycles n/p type pMeT-based supercapacitors and hybrid supercapacitors with pMeT as positive electrode active material and activated carbon as negative. The results of this investigation demonstrate that a conventional polymer such as pMeT can be successfully used in the supercapacitor technology when a hybrid configuration is realized; its use is, indeed, a great advantage because the hybrid supercapacitor outperforms the double-layer carbon supercapacitors presently on the market in terms of specific energy and power. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Electrochemical supercapacitor; Hybrid supercapacitor; p-Doping; n-Doping; n/p type supercapacitor; Poly3-methylthiophene 1. Introduction Supercapacitors and batteries are energy storage and conversion systems which satisfy, in a comple- mentary way, the requirements of high specific power and energy, respectively. In the last years, the signi- ficative advances achieved in the materials for super- capacitors brought about an extension of their application to the field of rechargeable batteries and, at present, the best performing devices on the market are the double-layer supercapacitors with activated carbons of high surface area (1500–2400 m 2 g À1 ) as electrode active materials. Amelioration in these types of devices is expected by lowering the equiv- alent series resistance (ESR) and this can be attained by optimizing the pore size distribution of the carbon materials. Electronically conducting polymers (ECPs) are promising materials for the realization of high per- formance supercapacitors, as they are characterized by high specific capacitances (the charge processes per- tain to the whole polymer mass and not only to the surface, as in the case of double-layer activated carbons) and by high conductivities in the charged states; furthermore, their charge–discharge processes are generally fast. These features suggest the possi- bility to develop devices with low ESR and high specific energy and power. The most promising poly- mer supercapacitor configuration in terms of charge storage capacity and cell voltage and able to outper- form the double-layer carbon supercapacitors is the n/ p type, i.e. the configuration in which an n-doped 0167-2738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-2738(02)00093-0 * Corresponding author. Tel.: +39-051-209-9798; fax: +39-051- 209-9365. E-mail address: mastrag@ciam.unibo.it (M. Mastragostino). www.elsevier.com/locate/ssi Solid State Ionics 148 (2002) 493 – 498