Electrochemical impedance spectroscopic study of dimensionally stable anode corrosion

• Published in: Journal of applied electrochemistry Vol. 28; no. 9; pp. 899 - 905
• Main Authors: ALVES, V. A, DA SILVA, L. A, BOODTS, J. F. C
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01-09-1998
• Subjects: Chemistry; Electrochemistry; Electrodes: preparations and properties; Exact sciences and technology; General and physical chemistry; Other electrodes; Ternary compound; Electrode impedance; Scanning electron microscopy; Iridium Oxides; Transition metal; Experimental study; Acidic solution; Surface structure; Titanium Oxides; Electrodes; Corrosion; Perchloric acid; Electrode reaction; Morphology; Titanium; Electrochemical reaction
• ISSN: 0021-891X; 1572-8838
• DOI: 10.1023/A:1003431130954

An electrode of nominal composition Ti/Ir sub 0.3 Ti sub 0.7 O sub 2 was prepared by thermal decomposition of the chloride precursor mixture at 450 deg C. A systematic study of the corrosion behaviour of this anode was performed under accelerated conditions (j=400 mA cm exp -2 ) in acidic media. Simultaneously, CV and EIS measurements were done at regular time intervals until the end of the electrode service life (approx528 h). It was possible to identify the various stages of the electrode deactivation, and quantify the associated parameters. Three main steps were identified in the electrode deactivation mechanism. During the first 170 h, the loss of the more external (porous) part of the oxide active layer occurred. This is supported by the decrease in the parameter-values related to the electrochemically active surface area of the anode (q sub a and C sub dl ) and an increase in the R sub ct -values. The second stage is evidenced by a potential step afterwards remaining practically constant up to approx380 h, suggesting that the more compact and still very active region of the electrode is now exposed. Finally, for t sub cor > 400 h the anode potential increases again. This behaviour, together with the R sub ct against time, suggests that the most internal part of the original coating, less rich in IrO sub 2 , is now exposed to the solution and is corroded. For t > =approx510 h the anode potential increases rapidly, the electrode being totally deactivated at tapprox =528 h, when the anodically grown TiO sub 2 film is exposed to the solution. During the complete deactivation process, the growth of a TiO sub 2 film, due to Ti-support oxidation, in addition to that already present (IrO sub 2 doped TiO sub 2 film formed during the calcination step), is evidenced by the increase in the R sub f -values, as well as decreasing C sub f -values. However, for t sub cor < 450 h the rate of this process is not significant. Only for t sub cor > 450 h Ti-support oxidation becomes the main feature of the deactivation process.