Sonochemical-Assisted In Situ Electrochemical Synthesis of Ag/α-Fe₂O₃/TiO₂ Nanoarrays to Harness Energy from Photoelectrochemical Water Splitting

Numerous protocols in heterostructure engineering hold promise for effectively improving the optical properties of nanomaterials for energy-harvesting applications. In this work, we successfully fabricated Ag/α-Fe₂O₃/TiO₂ heterostructures via electrochemical anodization assisted by pulse sonication. The morphological features of the silver (Ag) deposited on α-Fe₂O₃/TiO₂ showed a layered distribution of the α-Fe₂O₃ nanoparticles (NPs) over the TiO₂ nanotube arrays (NTAs), whereas Ag existed in a pseudocubical form. X-ray diffraction (XRD) patterns and X-ray photoelectron spectrometer (XPS) analysis validated the formation of α-Fe₂O₃ and anatase TiO₂ crystalline phases and Ag/α-Fe₂O₃/TiO₂ heterostructure. The diffuse reflectance spectroscopy (DRS) UV–vis spectroscopy results displayed a gradual decrease in the band gap with enhanced absorption in the visible region of the spectrum due to optically active heterostructure formation in the order Ag/α-Fe₂O₃/TiO₂ (470 nm) > α-Fe₂O₃/TiO₂ (424 nm) > TiO₂ (386 nm). The DRS absorption spectrum of Ag/α-Fe₂O₃/TiO₂ also exhibits a characteristic plasmon shoulder of Ag at ∼420 nm. The photocurrent density of Ag/α-Fe₂O₃/TiO₂ (2.59 mA/cm²) is almost 2.5- and 5-fold higher than that of α-Fe₂O₃/TiO₂ (1.05 mA/cm²) and pristine TiO₂ (0.54 mA/cm²), respectively, which can be related with the plasmonic behavior of Ag and lower band gap of α-Fe₂O₃. The results of electron impedance spectroscopy (EIS) analysis also showed facile charge transfer in the same order observed using UV–vis spectroscopy. These results demonstrate the effectiveness of the in situ electrochemical protocol to fabricate tunable heterostructures for efficient solar-driven water splitting