When coated on top of Ir-based dimensionally stable anodes, binary Bi–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 further clarification. This study prepared BixTi10-xOy heterojunction layers on an existing Ir7Ta3Oz anode by thermal decomposition (425 °C) of TiOSO4 and Bi(NO3)3 under varied Ti:Bi ratios and precursor matrix (inorganic versus organic solvents). Plain material characterizations (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 top BixTi10–xOy was nominated as the Cl– binding site with Ir7Ta3Oz as the ohmic contact. Bi12TiO20 and β-Bi2O3 (formed at x > 5) on the outer layer could elevate the reactivity of surface bound hydroxyl radicals and the ClER selectivity. However, relatively loosely packed and thick overlayers (due to glycolate and isopropanol in precursor) aggravated the current and energy efficiency of ClER as well as the anodic stability.​