Ti|Ir-Sn-Sb oxide anode: Service life and role of the acid sites content during water oxidation to hydroxyl radicals

This work describes the preparation of four Ti|Ir-Sn-Sb oxide anodes by the Pechini method under different conditions and the evaluation of their service life, envisaging a future application in electrochemical advanced oxidation processes for water treatment. This was estimated by means of accelerated life tests (1 A cm−2, 1 M HClO4), which highlighted the dependence of durability on the Ir and Sn content in the mixed metal oxide (MMO) as well as on the required heat treatment time for its preparation. The best MMO anode reached up to 351 h of service life under such extreme conditions. SEM-EDS and XRD analyses were performed before and after the accelerated life tests, evidencing that the failure of the MMO coatings occurred by detachment from the titanium substrate, thus losing the anode electroactivity. Great amounts of acid sites in the range 0.21-0.26 meq g−1 were determined on the MMO surfaces by Boehm titrations. From the apparent rate constants determined for the decay of N,N-dimethyl-4-nitrosoaniline used as spin trap, before and after acid sites neutralization, a higher activity of adsorbed hydroxyl radicals at the MMO surface cannot be correlated with a greater amount of acid sites. The results obtained suggest that other active sites affect the formation of such radicals from water discharge.