A study on corrosion and deactivation mechanism of Pt/Nb anodes in sodium chlorate containing solution using EIS

• The electrochemical production of sodium perchlorate is one of the main applications of Pt/Nb or Pt/Ti anode.
• The corrosive solution can diffuse through the cracks and cause a passive layer to form on the substrate and the platinum coating to dissolve.
• Low magnitude of Rf and high magnitude of Cf implicates low thickness of the passive layer (Nb2O5) on the substrate.
• The passivation of substrate is the main reason behind the Pt/Nb anode deactivation.

Due to their high price, the corrosion resistance and lifetime of Pt/Nb anodes, which are usually manufactured through an electrodeposition process, in the sodium perchlorate production is important. In this research, the effect of electrodeposition parameters on the corrosion behaviour of these anodes has been studied. The samples were produced through electrodeposition of platinum on niobium at current densities, electrolyte temperatures and, finally, electrodeposition time extensions. The coated samples were then exposed to accelerated life testing in sodium chlorate containing solution at different extensions. EIS spectra of the samples were obtained in sodium chloride solution at the above-mentioned time intervals. The analysis of EIS spectra showed that the highest corrosion resistance was for the sample electrodeposited for 75 min at current density of 5 mA·cm− 2 and electrolyte temperature of 93 °C. The low thickness of the niobium oxide passive layer in this sample and the presence of more catalytic platinum coating are the reasons for its higher corrosion resistance compared to the samples electrodeposited under other conditions. Therefore, the passive layer of the other samples is thick and more platinum has been dissolved in the solution.

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