EIS Analysis on the Effect of Current Density on Corrosion Behavior of Platinum Anodes in Sodium chlorate electrolysis cell

Platinum anodes, including platinum coating on the substrate of niobium, are used for electrolysis of sodium chlorate. Due to the high price of these anodes, their corrosion resistance in this environment is important. In this research the effect of current density has been investigated on corrosion the behavior of Pt/Nb anode. Platinum coating was deposited on the niobium substrate by electrodeposition method. The samples were then exposed to accelerated life test in chlorate electrolysis cell at current densities of 0.5, 1.2 and 2 A/cm2 for 3, 10, 40 and 70 hours at constant temperature of 35°C. Cyclic voltammetry and electrochemical impedance spectroscopy was done on the samples at each time extension. The samples finally were characterized using SEM. The results showed that at any current density, the solution in the vicinity of the anode is acidic and with increasing current density, the corrosion of the coating through the formation of chloroplatin complexes, from local to uniform, is converted at a high rate.As well as, it was revealed that the Pt/Nb anodes are deactivated in to two manners; Spontaneous dissolution of platinum coating and growth of passive layer or dissolution of coating together with passive layer. The electrolysis with current density of 1.2 A/cm2 is the best operating condition in which the platinum anode has its highest corrosion resistance, lowest destruction and optimum catalytic effect.