Anodic corrosion of indium tin oxide films induced by the electrochemical oxidation of chlorides
Conducting tin-doped indium oxide (ITO) films were prepared by spray\npyrolysis for study of their electrochemical stability as anodes\nin chloride solutions. From reflection high energy electron diffraction\nand transmission electron microscopy observations, ITO films present\na regular polycrystalline structure with a very low density of twins.\nCorrosion was investigated by in situ mass measurements with a quartz\ncrystal microbalance (QCM) and by direct imaging of corrosion morphology\nwith scanning (SEM) and transmission (TEM) electron microscopy. Corrosion\nwas found to occur at potentials positive of chloride oxidation (0.9\nV vs. saturated calomel electrode (SCE)) as long as oxygen is not\nevolved (V<1.3 V(SCE)). The corrosion rate is very low in the\npresence of 0.04 M HCl at pH 8 (â‰¤5 ng sâˆ’1 cmâˆ’2), and very large\nin acidic HCl solutions (3400 ng sâˆ’1 cmâˆ’2 in 0.1 M HCl). TEM\nimages of corroded ITO membranes reveal an important intergranular\nattack. The corrosion mechanism is based on the electrochemical formation\nof ClÂ° and OHÂ° radical species able to withdraw electrons from\nIn-O surface bonds.