Performance evaluation of CNT/polypyrrole/MnO2 composite electrodes for electrochemical capacitors

A ternary composite of CNT/polypyrrole/hydrous MnO2 is prepared by in situ chemical method and its electrochemical performance is evaluated by using cyclic voltammetry (CV), impedance measurement and constant-current charge/discharge cycling techniques. For comparative purpose, binary composites such as CNT/hydrous MnO2 and polypyrrole/hydrous MnO2 are prepared and also investigated for their physical and electrochemical performances. The specific capacitance (SC) values of the ternary composite, CNT/hydrous MnO2 and polypyrrole/hydrous MnO, binary composites estimated by CV technique in 1.0 M Na2SO4 electrolyte are 281, 150 and 35 F g(-1) at 20 mV s(-1) and 209, 75 and 7 Fg(-1) at 200 mV s(-1), respectively. The electrochemical stability of ternary composite electrode is investigated by switching the electrode back and forth for 10,000 times between 0.1 and 0.9 V versus Ag/AgCl at 100 mV s(-1). The electrode exhibits good cycling stability, retaining up to 88% of its initial charge at 10,000th cycle. A full cell assembled with the ternary composite electrodes shows a SC value of 149 F g(-1) at a current loading of 1.0 mA cm(-2) during initial cycling, which decreased drastically to a value of 35 F g(-1) at 2000th cycle. Analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Brunauer-Emmet-Teller (BET) surface area measurement and inductively coupled plasma-atomic emission spectrometry (ICP-AES) are also used to characterize the composite materials. (C) 2007 Elsevier Ltd. All rights reserved.