A composite consisting of polypyrrole and cellulose from the Cladophora sp. green algae is shown to exhibit excellent cycling stability when used as the electrodes in an aqueous symmetric supercapacitor device. The capacitance of the device, which was 32.4 F g- 1, only decreased by 0.7% during 4000 galvanostatic cycles employing a current of 10 mA and potential cut-off limits of 0 and 0.8 V. No change in the electrode material's morphology could be seen when comparing cycled and pristine materials with scanning electron microscopy. Furthermore, no significant loss in capacitance was observed even when charging the device to 1.8 V. Measurements of the electrode potentials versus a common reference show that this effect was due to a device intrinsic self-protective mechanism which prevented degradation of the polypyrrole.
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