Synthesis, characterization and photoelectrochemical performance of Bi2Fe4O9 thin films

Mullite-type Bi 2 Fe 4 O 9 has been little explored in thin film form as a photoanode for photoelectrochemical water splitting. In this study, Bi 2 Fe 4 O 9 thin films have been prepared using the sol-gel technique from a simple precursor solution based on the corresponding metal salts, acetic acid, and polyvinyl alcohol. The films were deposited by dip-coating onto fluorine-doped tin oxide substrates and dried at 350 °C, repeating the dipping-drying cycle six times, and finally sintered at 600 °C. The films were characterized by GIXRD, revealing the formation of the material in its orthorhombic phase. Raman spectroscopy showed the A g and B 1g vibrational modes, validating the formation of the bismuth iron oxide. UV–Vis transmittance measurements revealed that the material exhibits two optical transitions: a direct band gap of 2.86 eV and an indirect band gap of 1.98 eV. FESEM micrographs and AFM images showed a uniform nanostructured surface morphology. The photoelectrochemical properties of the Bi 2 Fe 4 O 9 films were studied using cyclic voltammetry and chronoamperometry with front side illumination, demonstrating the stability of the material in aqueous media and the generation of photocurrent in the presence of H 2 O 2 . Furthermore, results from intensity-modulated photocurrent spectroscopy (IMPS) revealed that the photocurrent is limited by both bulk and surface recombination and a short hole diffusion length. • Orthorhombic Bi 2 Fe 4 O 9 thin films were prepared by a simple Sol-gel procedure. • The films show a direct band gap of 2.86 eV and an indirect one of 2.15 eV. • The films generate a stable anodic photocurrent in the presence of H 2 O 2 . • The photocurrent is limited by recombination and a short hole diffusion length.