Enhanced Water Oxidation of Hematite Photoanodes via Localized n‐p Homojunctions Induced by Gradient Zn²⁺ Doping

Abstract Constructing an internal electric field (IEF) within the hematite (Fe₂O₃) photoanode for highly efficient water oxidation performance with facilitated charge transfer and separation remains still a significant challenge. Unlike the conventional approach of creating interfacial electric fields through heterojunction design by introducing another semiconductor, a novel strategy is proposed for engineering localized n‐p homojunctions on the surface of Fe₂O₃ photoanode using gradient Zn²⁺ doping strategy. By implementing this approach, the inherent n‐type characteristics of Fe₂O₃ can be transformed into p‐type, thereby facilitating the formation of an n‐p junction with robust IEF, which enables more efficient charge separation and transfer. Additionally, the gradient Zn²⁺ doping is accompanied by the generation of oxygen vacancies, which further improves the charge transfer efficiency and accelerates water oxidation kinetics. As expected, the photocurrent density of optimized Fe₂O₃ photoanode at 1.23 V versus reversible hydrogen electrode is ≈2.6‐fold that of Fe₂O₃. This work provides a novel perspective on the design of localized n‐p homojunction within photoanodes for achieving high solar energy conversion efficiency.