Surface Rh-Boosted Photoelectrochemical Water Oxidation of α‑Fe₂O₃ by Reduced Overpotential in the Rate-Determining Step

The photoelectrochemical behavior of Rh cluster-deposited hematite (α-Fe₂O₃) photoanodes (α-Fe₂O₃@Rh) was investigated. The interactions between Rh clusters and α-Fe₂O₃ nanorods were elucidated both experimentally and computationally. A facile UV-assisted solution casting deposition method allowed the deposition of 2 nm Rh clusters on α-Fe₂O₃. The deposited Rh clusters effectively enhanced the photoelectrochemical performance of the α-Fe₂O₃ photoanode, and electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis were applied to understand the working mechanism for the α-Fe₂O₃@Rh photoanodes. The results revealed a distinctive carrier transport mechanism for α-Fe₂O₃@Rh and increased carrier density, while the absorbance spectra remained unchanged. Furthermore, density functional theory (DFT) calculations of the oxygen evolution reaction (OER) mechanism corresponded well with the experimental results, indicating a reduced overpotential of the rate-determining step. In addition, DFT calculation models based on the X-ray diffraction (XRD) measurements and X-ray photoelectron spectroscopy (XPS) results provided precise water-splitting mechanisms for the fabricated α-Fe₂O₃ and α-Fe₂O₃@Rh nanorods. Owing to enhanced carrier generation and hole transfer, the optimum α-Fe₂O₃@Rh3 sample showed 78% increased photocurrent density, reaching 1.12 mA/cm^–2 at 1.23 V_RHE compared to that of the pristine α-Fe₂O₃ nanorods electrode.