Tantalum oxide effect on the surface structure and morphology of the IrO2 and IrO2 + RuO2 + TiO2 coatings and on the corrosion and electrochemical properties of anodes prepared from these

Alterations in the phase composition, porosity, and surface morphology of coatings are examined following the insertion of a quantity of Ta2O5 into active coatings prepared from IrO2 or IrO2 + RuO2 + TiO2 (OIRTA). It is shown that even an insignificant concentration of Ta2O5 in a coating renders it substantially amorphous and leads to the appearance of a large number of wide protracted cracks in the coating. The latter extends the surface of anodes and boosts their apparent catalytic activity in the chlorine evolution reaction. In addition, this accelerates the diffusion of chloride ions toward the front surface of anodes, which noticeably reduces the overvoltage of the chlorine evolution reaction when manufacturing sodium chlorate. The coatings’ amorphization and the development of their surface substantially reduce the corrosion resistance of these anodes as compared with OIRTA.