Lattice and Surface Engineering of Transition Metal Oxide Photoanodes for Efficient Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for converting solar energy into hydrogen, yet the performance of transition metal oxide (TMO) photoanodes remains limited by insufficient visible‐light absorption, short charge‐carrier diffusion lengths, severe surface recombination, and sluggish oxygen evolution reaction (OER) kinetics. To overcome these intrinsic limitations, lattice engineering and surface engineering have emerged as effective strategies for modulating both bulk and interfacial processes. In this review, we present a unified structure−property framework centered on three representative approaches: (i) phase engineering, (ii) facet engineering, and (iii) atomic vacancy engineering. These strategies regulate crystal structure, exposed surfaces, and defect chemistry, thereby mitigating the intrinsic limitations of TMO photoanodes in light harvesting, charge transport, interfacial charge transfer, and surface reaction kinetics. Beyond individual effects, the interplay among these structural factors is also discussed to provide a more integrated understanding of PEC performance. This review further highlights that high‐performance PEC photoanodes require the coordinated optimization of lattice structure, surface characteristics, and defect states rather than the isolated modification of a single structural parameter. Finally, the current challenges are summarized, and perspectives are outlined toward the rational design of highly efficient and durable PEC photoanodes for solar‐driven hydrogen production.