Electrochemical Chlorine Evolution by Bi-Ti Oxide with a Heterojunction on Ir-Ta Oxide: Insights from the Effects of Layer Configurations

When coated on top of Ir-based dimensionallystable anodes,binaryBi-Ti oxides could enhance the chlorine evolution reaction(ClER) efficiency for chlor-alkali and mediated water treatment. However,the underlying mechanism and the effects of Bi necessitated furtherclarification. This study prepared Bi x Ti10-xO y heterojunctionlayers on an existing Ir7Ta3O z anode by thermal decomposition (425 degrees C) of TiOSO4 and Bi-(NO3)(3) under varied Ti:Bi ratiosand precursor matrix (inorganic versus organic solvents). Plain materialcharacterizations (scanning electron microscopy and X-ray diffraction)were performed together with voltammetry and potentiostatic electrolysis(in 50 mM NaCl, 50 mM HCOONa, and 0.1 M NaClO4). The topBi( x )Ti(10-x )O( y ) was nominated as the Cl- binding site with Ir7Ta3O z as the ohmic contact. Bi12TiO20 and beta-Bi2O3 (formed at x > 5) on the outer layer could elevate the reactivityofsurface bound hydroxyl radicals and the ClER selectivity. However,relatively loosely packed and thick overlayers (due to glycolate andisopropanol in precursor) aggravated the current and energy efficiencyof ClER as well as the anodic stability.

Automated summary

This study found that coating bismuth-titanium composite oxides on top of iridium-based anodes could enhance the efficiency of the chlorine evolution reaction for chlor-alkali and water treatment. The mechanism and effects of bismuth needed further clarification. Bi x Ti10-xO y heterojunction layers were prepared on an existing iridium-tantalum oxide anode, and various characterizations and electrolysis experiments were performed. The results showed that the outer layer of Bi12TiO20 and β-Bi2O3 could improve the reactivity and selectivity of the chlorine evolution reaction, but the loosely packed and thick overlayers worsened the efficiency and stability.