How Dimensionally Stable Anodes Used for Electrochemical Wastewater Treatment?

Jun 16, 2021

How Dimensionally Stable Anodes Used for Electrochemical Wastewater Treatment?

Dimensionally stable anodes (DSAs) have been investigated in electrochemical wastewater treatment. They typically consist of mixed metal oxide coatings on valve metal substrates. The functionality and selectivity of these electrodes are highly dependant on their physical structure and composition. These anodes conventionally use titanium as the substrate with either IrO2 or RuO2 as the electrocatalyst and TiO2, Ta2O5, ZrO2, or SnO2 as the stabilizer that also improves the selectivity of the anode. The oxide mixtures are usually prepared by thermal decomposition of precursor solutions. The resulting electrodes have a limited service life at high anodic potentials and elevated temperatures because the active oxides dissolve and the titanium substrate undergoes significant oxidation; these processes increase the anode resistance until it is no longer feasible to use them. The anode stability can be improved by modifying the composition and structure of the coating.

Sol-gel processing allows for easy adjustment of both of these properties and can lead to considerable changes in service life. Sol-gel processes are based on the hydrolysis of molecular precursors, such as metal alkoxides, in aqueous solutions. A benefit of this approach is that the weak interactions, including Vander Waals forces and hydrogen bonding, are not broken. These interactions lead to the formation of self-assembled structures in the oxide network. Also, extended mixing of these solutions leads to improved electrochemical behavior due to a more homogenous coating. Ta2O5 is often used as the stabilizing element in mixed oxide coatings because it is highly resistant to corrosion; however, it is conventionally mixed with an electrocatalyst in order to obtain a conductive coating.  

Electrodes with mixed oxide coatings of ruthenium oxide and titanium oxide on titanium substrates prepared by sol-gel methods and thermal decomposition. Mixed oxide coating prepared by the sol-gel process remained active longer but was inactivated through the dissolution of ruthenium species, making the near-surface 12layer of the coating rich in titanium oxide. Conversely, the anodes produced through thermal decomposition were inactivated by the growth of an insulating layer between the coating and the substrate.