Han Fu, Daisuke Ioka, Zhenhua Pan
The global transition from fossil fuels to renewable energy demands innovative hydrogen production technologies, with photocatalytic water splitting emerging as a sustainable and eco-friendly solution. In this process, photocatalysts harness sunlight and split water into hydrogen and oxygen, offering a clean and efficient means of solar energy conversion. Among different photocatalyst materials, transition-metal-doped perovskite oxides (TMPOs) have attracted attention for their visible-light activity, structural flexibility, and stability. Compared with other oxide semiconductors, TMPOs can host a wide variety of dopants at both the A- and B-sites, which makes it possible to tune the band structure while still keeping the perovskite lattice intact. This combination of resilience and tunability has led to benchmark results in one-step and Z -scheme water splitting, making TMPO a key material platform in photocatalysis research. They are also useful as model systems for studying defect chemistry, carrier dynamics, and dopant interactions, knowledge that can be applied to other oxide photocatalysts. In this review, we highlight the evolution of TMPOs from bandgap-tuned materials to nanostructured platforms. We propose that their future lies in precise defect control, scalable synthesis, and performance validation under real-world conditions. By positioning transition-metal doping as a core design principle, this work outlines a roadmap toward practical applications of TMPO-based systems in catalytic energy technologies.