Journal of Power Sources 162 (2006) 735–737 Short communication A novel galvanostatic polymerization for high specific capacitance poly(3-methylthiophene) in ionic liquid Catia Arbizzani, Francesca Soavi, Marina Mastragostino ∗ Dipartimento di Scienza dei Metalli, Elettrochimica e Tecniche Chimiche, Via S. Donato 15, 40127 Bologna, Italy Received 12 June 2006; accepted 16 June 2006 Available online 9 August 2006 Abstract For the first time it is here reported a novel and clean galvanostatic procedure to polymerize poly(3-methylthiophene) in the 1-ethyl- 3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI) ionic liquid (IL). The strategy consists in the use of the acid additive trifluoromethanesulfonimide (HTFSI) displaying the same anion of the IL and which provides an acid proton that is reduced to H 2 at the counter electrode upon the anodic polymer growth on the working electrode and prevents consumption of the ionic liquid with great advantage in terms of costs. This procedure provides a pMeT electrode featuring 250 F g -1 in EMITFSI at 60 ◦ C, a very interesting result in view of application of such pMeT in IL-based hybrid supercapacitors. Here are reported the results of the galvanostatic polymerization of pMeT in EMITFSI–HTFSI as well as the performance in EMITFSI at 60 ◦ C of the obtained pMeT electrode. © 2006 Elsevier B.V. All rights reserved. Keywords: Poly(3-methylthiophene); Galvanostatic electropolymerization; Supercapacitor; Ionic liquid 1. Introduction Supercapacitors of high specific power and energy play a crucial role in the development of electric and hybrid vehi- cles, where they may provide the required power peaks during acceleration and energy recovery during braking [1]. The typi- cal operating temperatures for such application are higher than room temperature (RT) and do not allow the use of commer- cially available double layer carbon supercapacitors based on low boiling point organic electrolytes such as acetonitrile as well as worse the performance of those featuring propylene car- bonate (PC). The use of ionic liquids (ILs) as electrolytes for supercapacitors is a very promising strategy to increase the max- imum operating voltage and hence the energy and power of these electrochemical devices at temperatures higher than RT [2–4]. The viability of ionic liquids has been already demonstrated in a hybrid supercapacitor with carbon as negative and poly(3- methylthiophene) (pMeT) as positive electrode over more then 15,000 cycles with cell voltage higher than 3.4 V at 60 ◦ C. This very interesting result was achieved with electrode materials ∗ Corresponding author. Tel.: +39 051 2099798; fax: +39 051 2099365. E-mail address: marina.mastragostino@unibo.it (M. Mastragostino). which were developed for operation in conventional organic electrolytes, and that displayed high specific capacitances in PC-based electrolyte but significantly lower values in the inves- tigated ILs [3,4]. To further increase the performance of the IL-based hybrid supercapacitor the polymer and carbon electrode materials should be properly designed in view of their use in the IL. As it concerns the conducting polymer, it has been demonstrated that electrochemical polymerization in the same IL used for capac- itance tests provides high performing polymers [4,5] and in the case of pMeT a high specific capacitance value of 195 F g -1 at 60 ◦ C in IL can be obtained [4]. However, this result has been obtained by voltammetric polymerization which cannot be used for preparation of large amount of pMeT, whereas galvanos- tatic technique is more viable for practical applications. The main drawback with galvanostatic preparation of large quanti- ties of polymer is the formation of by-products at the counter electrode which typically poison the polymerization bath as elec- tropolymerization proceeds, and this is more important when cells without separate compartments for the working and counter electrodes are used. In the case of the electropolymerization in IL at the counter electrode takes place the reduction of the IL which is progressively poisoned and consumed and this is a great disadvantage given its high cost. Thus, it is necessary 0378-7753/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2006.06.051