Enhanced Water‐Splitting Performance of Hematite Photoanodes via Fluorine‐Induced Carrier Dynamics and Lattice Oxygen Activation

Abstract Fluorine (F) has emerged as a critical dopant for enhancing the performance of hematite (Fe ₂ O ₃ ) photoanodes in photoelectrochemical (PEC) water oxidation; however, its functional mechanisms remain to be fully elucidated. This study systematically demonstrates that F‐doping improves Fe ₂ O ₃ ‐based photoanodes through dual effects involving increasing charge carrier density through electron structure modulation and activating the lattice oxygen oxidation mechanism by activating lattice oxygen and optimizing intermediate adsorption. The dual effects are strongly correlated with improved charge separation efficiency and charge injection efficiency across a series of Fe ₂ O ₃ and (oxy)hydroxide/F‐Fe ₂ O ₃ photoanodes. These dual effects are optimally integrated into the F‐NiFe/F‐FeOOH/F‐AlOOH/F‐Fe ₂ O ₃ architecture, where precisely aligned hole‐trap energy levels enable exceptional performance (4.04 mA cm ⁻² at 1.23 V _RHE , applied bias photon‐to‐current efficiency = 0.62%). This work provides novel insights into the effects of F doping and proposes an integrated design strategy for optimizing its impact, advancing the field of PEC water splitting.