A tantalum electrode on which polypyrrole (PPy) had been previously formed by electropolymerization was galvanostatically electrolyzed in an aqueous solution of 0.01 wt% phosphoric acid. This process contains the irreversible oxidation of a PPy film, the decomposition of solvent, and the formation of Ta2O5 by the reaction of OH− coming through the PPy film, with Ta electrodes. A three layer‐structure (PPy/Ta2O5/Ta) was confirmed by electron spectroscopy for chemical analysis (ESCA). A PPy film containing CIO4 − as dopant [PPy(CIO4 −)] was significantly deteriorated in comparison with PPy(TsO−) at the electrolysis. Therefore, the (PPy(TsO−)/Ta2O5/Ta) system showed better electrical characteristics as a capacitor than the (PPy(CIO4 −)/Ta2O5/Ta) system showed better electrical characteristics as a capacitor than the (PPy(ClO4 −)/Ta2O5/Ta) system.
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