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Communications was dried only to about 30 of its weight before the crosslinking step A drop of 1 M MgSO4 was added for the crosslinking and after about 15 min the electrode was equilibrated with aqueous 0 25 M MgSO4 for at least 2 h The PPy was grown on the polymer gel as described above The unswelled PEDOT PSS PPy electrode was prepared by electropolymerizing pyrrole on an uncrosslinked PEDOT PSS coated electrode from acetonitrile solution containing 0 25 M pyrrole and 0 1 M LiClO4 at a constant potential of 0 85 V vs an Ag AgCl electrode The PPy coated electrode was prepared by growing PPy on a gold electrode under the same conditions as in the case of PEDOT PSS PPy electrodes The electrochemical cell in the supercapacitor geometry for the cyclic voltammetric and the chrono potentiometric studies was a two electrode set up with two identical electrodes face to face and parallel in aqueous 1 M Na2SO4 For the swelled polymer electrodes i e in the cases where high power density was applied the electrodes were at a fixed separation of 1 mm whereas in other cases the distance was about 1 cm The cells were in ambient atmospheric conditions The chrono potentiometric studies of galvanostatic charging discharging were carried out in the potential range of 0 V to 0 8 V For calculation of the energy and power densities the first discharge curve after equilibration of the cell at 0 8 V was analyzed and the dry mass of the polymeric material on a single electrode was considered The mass of the PEDOT PSS was determined from the weight of the dispersion of known concentration that was applied to the electrode The mass of PPy was calculated from the coulomb of charge passed for its electropolymerization assuming 2 25 electrons per pyrrole unit are needed for the polymerization of PPy at 25 doping level Received January 14 1999 Final version June 7 1999 1 G S Attard P N Bartlett N R B Coleman J M Elliott J R Owen J H Wang Science 1997 278 838 2 C Niu E K Sichel R Hoch D Moy H



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