Electrocatalytic activities of Sb-SnO2 and Bi-TiO2 anodes for water treatment: Effects of electrocatalyst composition and electrolyte

Abstract

This study compares the electrocatalytic behavior and performance of metal-doped oxide anodes in widely employed electrolytes (i.e., Na2SO4, NaClO4, and NaCl). Sb-doped SnO2 (Sb-SnO2), Bi-doped SnO2 (Bi-SnO2), or Bi-doped TiO2 (Bi-TiO2) are coated onto a Ta-doped IrO2 (Ta-IrO2) electrode using identical fabrication procedures involving coating and annealing cycles. The resultant electrodes display porous morphologies with interparticle connections. Crystalline phases of Sb-associated oxides are not evident in Sb-SnO2, whereas distinct Bi2O3 phases are observed in Bi-SnO2 and Bi-TiO2 because the radius of Bi3+ is larger than those of the base metals. Sb-SnO2 exhibits the highest electrocatalytic activity for the decomposition of phenol irrespective of the type of electrolyte, whereas the activity of Bi-SnO2 is always poor. The activity of Bi-TiO2 is poor in sulfate and perchlorate electrolytes; in contrast, it is remarkably enhanced and comparable to that of Sb-SnO2 in chloride electrolyte. Such chloride-specific activity of Bi-TiO2 is attributed to the effective generation of reactive chlorine species, whereas the generation of OH radicals is limited. On the other hand, Sb-SnO2 effectively catalyzes the generation of OH radicals, leading to mediated generation of reactive chlorine species. The decomposition of phenol is further examined in terms of reaction intermediates and CO2 production using Sb-SnO2 and Bi-TiO2 anodes in sulfate and chloride electrolytes. The electrocatalyst and electrolyte-dependent mechanism is discussed.