Characterization of Lifetimes and Mode of Deactivation of Dimensionally Stable Anodes in Current Reverse Applications

"The effect of current reversal on two commercially manufactured electrodes (RuO2-TiO2 and IrO2-Ta2O5 coated Ti) in a chloride bearing electrolyte was evaluated. Accelerated lifetimes were found to decrease with increasing current density and increasing reversal frequency. Ru: Ti coated electrodes exhibited longer lifetimes than Ir: Ta coated electrodes even though they had one-third as much precious metal content. Chloride concentration did not affect lifetime in the range examined. Using energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS), the failure mode of the electrodes was determined to be coating dissolution leading ultimately to passivation by the presumed growth of a highly resistive oxide at the coating/substrate interface.INTRODUCTIONCatalytic titanium anodes (CTAs) were developed in the 1960’s to replace graphite anodes in chlor-alkali cells. CTAs exhibited much better dimensional stability than graphite leading to lower operating potentials by promoting smaller electrode gaps and better operational efficiencies as they had to be replaced less often. CTAs are simply Ti substrates coated with precious metal oxides (such as IrO2 and RuO2) mixed with other components (such as TiO2 and TasO5) (Trasatti, 2000).CTAs are used in many other electrochemical industries, including water disinfection, wastewater treatment, cathodic protection and metal plating. RuO2 based coatings are typically used for chlorine evolution. IrO2 based coatings are for the most part utilized for oxygen evolution (Comninellis & Nerini, 1991; Forti, Olive, & De Andrade, 2001; Kotz, Stucki & Carcer, 1991; Trasatti & Lodi, 1981)"