Surface Activation of NiMo Oxyfluoride/Fe‐Oxyhydroxide Heterostructures via Defect Engineering for Enhanced Photoelectrochemical Water Oxidation

ABSTRACT Efficient photoelectrochemical water oxidation critically depends on bulk conductivity and effective charge separation at the semiconductor electrolyte interface. Herein, we report a hybrid heterostructure design strategy using nickel molybdenum oxyfluoride (NiMoOF) with iron oxyhydroxide (FeOOH), synthesized through a hydrothermal synthesis route combined with subsequent spray pyrolysis. The hybridization of NiMoOF and FeOOH in a NiMoOF/FeOOH hybrid heterostructure significantly increases the surface‐active area and promotes interfacial charge transfer by passivating surface defects, compared to pristine NiMoOF. As a result, the NiMoOF/FeOOH hybrid heterostructured photoanode exhibits a markedly enhanced photocurrent density of 2.18 mA cm ⁻² at 1.23 V vs. RHE, substantially outperforming pristine NiMoOF. The photoanode also demonstrates excellent operational stability maintained over 20 h under 1.5 illumination. Furthermore, quantitative analysis reveals significant improvements in both bulk (η _bulk = 28.91%) and surface (ηs _urface = 90.38%) charge separation efficiencies. This work demonstrates a scalable and effective strategy for designing high‐performance photoanodes through synergistic compositional and interfacial engineering, offering valuable insights into advanced photoelectrochemical water‐splitting systems.