Synergistic effects of successive Pt/Si co-doping on Fe₂O₃ photoanode for improved photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is a green technology that converts solar energy into hydrogen fuel. Hematite (Fe₂O₃) is considered a promising photoanode for PEC applications due to its narrow bandgap, natural abundance, and strong stability in aqueous environments. However, its poor conductivity and severe charge carrier recombination hinder its PEC performance. To address these limitations, this study adopts a co-doping strategy using an ex-situ dipping technique to sequentially incorporate Pt and Si into Fe₂O₃. Pt/Si co-doping significantly enhanced bulk conductivity by lowering the bulk charge transfer resistance. Additionally, a high-temperature heat treatment leads to the formation of a SiO_x overlayer on the surface, which reduced surface charge transfer resistance and improved hole transfer to the electrolyte for efficient water oxidation. The co-doped Fe₂O₃ photoanode achieved a photocurrent density of 1.52 mA/cm² at 1.23 V_RHE, which is 58 % higher than that of undoped Fe₂O₃. It also exhibited a 24 % incident photon-to-current conversion efficiency at 380 nm. With Co-Pi cocatalyst loading, the performance further improved to 1.66 mA/cm², along with hydrogen and oxygen evolution rates of 76.32 and 31.9 μmol/h, respectively. This work highlights the effectiveness of dual-ion doping and overlayer engineering for developing high-efficiency PEC photoanodes.