Long Cycle Life Nanocellulose Polypyrrole Electrodes
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Long Cycle Life Nanocellulose Polypyrrole Electrodes Gustav Nyström1, Henrik Olsson1, Martin Sjödin1, Daniel O. Carlsson1, Albert Mihranyan1, Leif Nyholm2 and Maria Strømme1 1
Division of Nanotechnology and Functional Materials, The Ångström Laboratory, Uppsala University, Box 534, 751 21 Uppsala, Sweden
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Department of Materials Chemistry, The Ångström Laboratory, Uppsala University, Box 538, 751 21 Uppsala, Sweden ABSTRACT
A polypyrrole (PPy) nanocellulose composite was shown to cycle well over 3000 cycles in 2.0 M NaCl electrolyte when used as the active material for both electrodes in an energy storage device. SEM micrographs show a highly porous nature of the conductive paper material and electrochemical charge-discharge measurements, as well as external electrode potential monitoring, confirm the good cycling behavior of the material. INTRODUCTION Limited cycling stability has long been considered one of the main drawbacks of conducting polymer based electrodes [1, 2]. Recent results, however, show progress towards acceptable cycle life [3-5]. In some cases, an improved cycle life was seen as a result of depositing the conducting polymer on a substrate, for instance PPy on Carbon nanotubes (CNTs) [6] or in a Nafion-PPy composite [7]. It was argued that the rigid CNT network may have a stabilizing effect on the PPy during cycling and that Nafion, besides having a mechanical stabilizing effect, also stabilizes the radical cations formed during the electrochemical oxidation of PPy. In both these studies, the CNT and Nafion composites showed a drastically improved cycle life compared to that of the pristine PPy polymer. We have recently reported on an electrode material consisting of cellulose nanofibers extracted from the green algae Cladophora subsequently coated with a thin layer of PPy [8-11]. This composite conductive paper material has a nitrogen BET surface area of 80 m2/g and was found to function as an electrode material in aqueous electrolyte all-polymer batteries [12]. In the present study, it is shown that long cycle life can be obtained with the present nanocellulose PPy electrodes in aqueous electrolytes. EXPERIMENT Cellulose from the Cladophora algae was extracted as previously described [13]. Preparation of the polypyrrole (PPy) nanocellulose composite has been described elsewhere [8]. In short, the nanocellulose PPy composite was prepared by thorough mixing of 300 mg Cladophora cellulose, well suspended in 100 mL water,
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with a 50 mL 0.43 M pyrrole solution followed by chemical polymerization of pyrrole on the cellulose fibers by adding 50 mL 0.3 M FeCl3 while stirring. The electrochemical characterizations were carried out using an Autolab PGSTAT302N potentiostat (Ecochemie, the Netherlands) and 2.0 M NaCl electrolyte solutions. A Pt auxiliary electrode (placed in a separate compartment) and a 3 M NaCl Ag/AgCl reference electrode were used in the 3-electrode measurements. For the 2electrode measurements, small sandwich type battery cells were assembled with a symmetric setup of two nano
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