Searching for breakthrough in seesaw-like contradictions to achieve high-efficiency solar-driven overall water splitting

The decisive challenge of the photocatalytic overall H2O splitting is to develop a cost-effective and stable photocatalyst that efficiently utilizes sunlight with a high solar-to-hydrogen energy (STH) conversion efficiency. For nearly half a century, lots of landmarks have been made in the basic research of photocatalytic overall H2O splitting. For instance, many ultraviolet-light driven photocatalysts are modified through various strategies to respond to visible light, and new visible light photocatalysts were constantly developed. There are also many modification protocols that can be used for reference to improve the charge separation efficiency and surface catalytic reaction. More importantly, preliminary exploration toward the large-scale practical application has been conducted in recent years. In this review, the basic principles of photocatalytic overall H2O splitting were first presented. Then, the modification tactics of photocatalysts aimed at overall improving the photocatalytic performance were detailly summarized. Highlights are the comparisons and discussions of five contradictions in realizing practical application of photocatalytic overall H2O splitting, with providing some insights on how to balance them. Finally, the research challenges and prospects to achieve scalable practical applications toward overall H2O splitting are proposed.