Photoelectrochemical Bi2Fe4O9 phase purification - Removing the phase Bi2O3 from Bi2Fe4O9/Bi2O3 thin films

Multiferroic photo(electro)catalysts hold significant potential for various applications, including hydrogen generation, water treatment, and sensor development. In this context, mullite-type bismuth ferrite (Bi2Fe4O9) emerges as a promising material due to its stability and suitable bandgap. However, regardless of the chosen and optimized synthesis protocol, the preparation of Bi2Fe4O9 often results in the formation of unwanted secondary phases, such as Bi2O3, Bi25FeO39, Fe2O3, and BiFeO3. While considerable efforts have been directed toward improving synthesis procedures, an alternative or complementary strategy lies in the development of an effective purification step-a path that has not been pursued until now. In this study, we successfully removed the Bi2O3 phase from Bi2Fe4O9/Bi2O3 thin-film photoelectrodes, achieving a pure Bi2Fe4O9 photoelectrode through a straightforward and accessible method that combines voltammetry and glycerol as a cost-effective complexing agent. Our findings highlight the critical role of the complexing agent in preventing the formation of bismuth(III) species, primarily in the forms of Bi2O3, Bi(OH)3, and BiOOH, within the photoelectrode. This simple yet innovative approach provides a promising pathway to eliminate undesirable secondary bismuth phases, paving the way for the efficient purification of bismuth oxide-based electrodes.