Zinc Oxide‐Based Nanocomposite Photoelectrodes for Photoelectrochemical Water Splitting: A Review on Structural Modifications and Performance Optimization

ABSTRACT Hydrogen is unique among clean energy sources because of its high energy density, environmental friendliness, and sustainability. For solar‐to‐hydrogen conversion, photoelectrochemical water splitting (PEC‐WS) has become a promising and sustainable technique. The development of stable and efficient semiconductor photoelectrodes is crucial for ensuring the effectiveness of PEC systems. Zinc oxide (ZnO) has attracted a lot of interest as a photoelectrode material among the various transition metal oxides because of its good electron mobility, favorable band alignment, structural flexibility, and chemical stability. In light of the extensive research on ZnO‐based photoanodes, this review aims to provide an in‐depth analysis of the latest advancements, challenges, and emerging perspectives in this field. Additionally, it emphasizes modulation techniques, including metal nanoparticle inclusion, heterojunction development, selective doping, morphological engineering, and defect tuning. Furthermore, a comprehensive discussion of the underlying mechanism, methods of synthesis, and performance trends is offered, highlighting the association between nanostructure design and photoelectrochemical efficiency. This review provides a comprehensive road map for further ZnO‐based photocatalyst optimization and modulation techniques.