Pulse-Plating Electrodeposition of Metallic Bi in an Organic-Free Aqueous Electrolyte and Its Conversion into BiVO₄ to Improve Photoelectrochemical Activity toward Pollutant Degradation under Visible Light

A low-cost and durable BiVO₄ photoelectrode (PE) is herein synthesized to improve the separation of the electron and hole pair in photoelectrochemical applications. A new synthesis method was envisaged depositing metallic Bi on fluorine-doped tin oxide (FTO) in a pure aqueous electrolyte containing Bi(NO₃)₃ and KI via pulse plating at room temperature (pH = 1). The Bi⁰ and intermediate oxides/hydroxides in low content were then transformed into BiVO₄ using thermal treatments. This procedure renders a rapid and low-cost fabrication method, enhancing the catalyst durability. X-ray diffraction and X-ray photoelectron spectroscopy analysis confirmed the composition of the Bi intermediate species during synthesis and the successful deposition of a monoclinic phase of BiVO₄. An optical band gap of 2.42 eV with n-type semiconductive features was estimated for the BiVO₄. An energy band diagram was proposed based on diffuse reflectance spectroscopy analysis and Mott-Schottky plots showing that the BiVO₄ surface was thermodynamically unfavorable to produce hydroxyl radicals. However, this PE presented a relevant photoelectrochemical activity under low energy illumination (Xe lamp) to conduct the degradation of pollutants via direct oxidation. Under this condition, the highest degradation percentage of sulfamethoxazole was achieved in photoelectrocatalysis (around 50%) in comparison with electrocatalysis, photolysis, and photocatalysis techniques. The FTO-BiVO₄ catalyst displayed adequate photostability and reusability during all testing.