Ruthenium based DSA in chlorate electrol

Ruthenium based DSA® have been investigated in chlorate electrolyte using rotating disks made from commercial electrodes. Measurements of the voltammetric charge, q*, and of iR-corrected polarisation curves up to current densities of 40 kA/m2 were recorded on new and aged anodes from 3 years of production in a chlorate plant. Anodic polarisation curves in chloride containing electrolytes bend towards a higher slope at approximately 1.2 V versus Ag/AgCl, likely due to oxidation of ruthenium. The potential and current density at which the curves bend have been defined as the critical potential, Ecr, and the critical current density, icr. New anodes operating at a relatively high potential, >Ecr, display an increase in real surface area, subsequently decreasing anode potential and selectivity for oxygen formation during initial months of operation. Experiments at constant ionic strength under chlorate process conditions demonstrated that Ecr decreased with increasing chloride concentration by a factor of -0.09 V/log Cl-, whereas icr increased with rising chloride levels. The chlorine evolution reaction exhibited first order behavior with respect to chloride concentration. A possible reaction mechanism for chlorine formation is suggested.