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.