Photocatalytic water splitting is a promising method for green hydrogen production. Great progress has been made in photocatalyst activity after decades of study. Cationic doping is one of the most extensively studied photocatalyst optimization strategies. Diverse findings, both positive and negative effects, have been reported, reflecting the complexity of the system. Thus, a deep understanding of both the fundamentals and current progress is essential for the rational exploration and development of this strategy. In this Review , we start by providing a brief introduction to the principles of photocatalytic water splitting and the evaluation indices of photocatalytic efficiency. Following that, we present the fundamentals of cationic doping, with special attention to the underlying thermodynamics and its modification of the structure and electronic structure of metal oxide photocatalysts. Building on this basis, we highlight recent progress in understanding how cationic doping affects fundamental steps in photocatalytic water splitting, with a focus on light absorption and charge transport. Finally, we summarize the current challenges and research gaps in the field.
Duan et al. (2026) studied this question.