Formation and electrochemical behaviour of poly(pyrrole) coatings on steel substrates

✍ Scribed by W. J. Hamer; L. Koene; J. H. W. de Wit

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: German
• Weight: 170 KB
• Volume: 55
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.200303778

✦ Synopsis

This paper focuses on the deposition process and the semi-conductive properties of PPy layers on steel. The polymerisation of PPy was performed galvanostatically on steel in an aqueous solution of 0.1 M pyrrole and 0.1 M oxalic acid (H 2 C 2 O 4 ) using a current density of 1 mA/cm 2 . The build-up of a ferrous oxalate (FeC 2 O 4 ) layer, which seals the seel substrate surface, is initially observed. PPy layers made by this method are always doped with oxalate anions. A mechanism is proposed in which PPy deposits at sites where ferrous oxalate is dissolved. PPy is a semiconductor, just like oxide films formed naturally on some metals. Mott-Schottky diagrams for 9.0, 11.6 and 15.0 kHz suggests a frequency dependence of the dielectric constant of polypyrrole (e PPy ). The flatband potential E FB was about À 0.39 V vs. NHE and the charge carrier density was estimated to be about 5 Á 10 20 m À3 . Also, in earlier work by Rammelt et al. and by Miller and Bockris (using different electrolytes and substrate materials) a frequency dependence has been found for a constant phase element that was used to describe the space charge capacitance C SC . The frequency dependence observed can partly be ascribed to surface roughness, which seems experimentally supported by SEM-research.