An effective synthesis route of reproducible Fe₂O₃ photoanodes for photoelectrochemical water splitting via photodiode-based heat treatment process

Iron oxide (Fe₂O₃) materials for photoelectrochemical (PEC) water splitting have garnered significant attention because of its 2.1 eV bandgap, theoretical solar-to-hydrogen conversion efficiency of 12.9 %, and high stability in neutral and alkaline environments. While various methods have been explored to enhance its PEC performance, nanorod-based Fe₂O₃ photoanodes have shown promising PEC performance. However, Fe₂O₃ nanorods have showed significant performance variations (e.g., 0.3–1 mA/cm² at 1.23 V vs. RHE), which have been attributed to the complex fabrication process, involving multiple heat-treatment steps and sensitive quenching procedures. In this study, we introduce a highly reproducible method for fabricating Fe₂O₃ photoanodes for PEC cells using a vertical-cavity surface-emitting laser (VCSEL) photodiode-based heat-treatment process. Compared to conventional heat-treatment methods, this approach not only enhances the reproducibility of the photoanodes but also considerably reduces the total fabrication time to only ∼7 min. Also, this approach does not increase the particle size of the FeOOH nanorods used as the precursor as confirmed by scanning electron microscopy. PEC performance evaluation reveals ∼50 % higher photocurrent density for photoanodes produced with our approach. To further improve PEC performance, Fe₂O₃ is doped with tetravalent elements (Zr, Ti, and Pt) and coated with oxygen evolution reaction catalysts using the VCSEL-based process.