Ultrathin multilayer Sb-SnO2/IrTaOx/TiO2 nanotube arrays as anodes for the selective oxidation of chloride ions

The oxidation of chloride ions (Cl−) to oxidized chlorine species (chlorine/hypochlorous acid/hypochlorite) is emerging as a promising alternative to the oxygen evolution reaction because it has a lower overpotential than the latter, and can also produce value-added anodic products. Here, an ultrathin multilayer electrode (Sb-SnO2/IrTaOx/TiO2 nanotube (TNT)) has been fabricated by simple dipping and electrodeposition methods for the production of hypochlorous acid by Cl− oxidation. The use of non-noble metal-based electrodes significantly reduced the use of noble metals and increased the selectivity for Cl− oxidation even at the neutral pH and low concentration of NaCl, resulting in the reduction of cost and energy consumption. The nanotube structure of Sb-SnO2/IrTaOx/TNT affords an increased active surface area and loading amounts of the catalysts compared to the structure of the flat electrodes, making the Sb-SnO2/IrTaOx/TNT more efficient than flat electrodes for Cl− oxidation. The Faradaic efficiency of Sb-SnO2/IrTaOx/TNT for Cl− oxidation was ∼95%, indicating that water oxidation was almost suppressed. Compared to the commercial dimensionally stable anode (DSA), the overpotential of Sb-SnO2/IrTaOx/TNT for water oxidation is much larger than for Cl− oxidation, therefore, the Sb-SnO2/IrTaOx/TNT could exhibit the high selectivity for Cl− oxidation by suppressing the competitive water oxidation.