Constructing Fe₂O₃/TiO₂ core-shell photoelectrodes for efficient photoelectrochemical water splitting

In this study, plasma enhanced chemical vapor deposition (PECVD) was utilized to co-axially modify hydrothermally grown Fe₂O₃ nanorod arrays by depositing a TiO₂ overlayer to create Fe₂O₃/TiO₂ core-shell photoelectrodes. Comprehensive structural (XRD, SEM, TEM) and compositional (XPS) analyses were performed to understand the effects of the TiO₂ shell on the PEC activities of the Fe₂O₃ core. It was revealed that the heterojunction structure formed between TiO₂ and Fe₂O₃, significantly improved the separation efficiency of photo-induced charge carriers and the oxygen evolution kinetics. A maximum photocurrent density of ∼900 μA cm^-2 at 0.6 V vs. saturated calomel electrode (SCE) was obtained for the Fe₂O₃/TiO₂ photoelectrodes, which was 5 and 18 times higher when compared to that of hydrothermally synthesized Fe₂O₃ and PECVD synthesized TiO₂ electrodes, respectively. Moreover, the Fe₂O₃/TiO₂ core-shell nanorod arrays displayed superior stability for PEC water splitting. During 5000 s PEC measurements, a steady decrease of the photocurrent was observed, mainly attributed to the evolution of oxygen bubbles adsorbed on the working electrodes. This observation was verified by the complete recovery of the PEC performance demonstrated for a second 5000 s PEC measurement carried out after a brief time interval (10 min) that allowed the electrode surface to regenerate.