Abstract: In recent years, S-scheme heterojunctions have garnered significant attention, with their carrier transfer mechanism primarily understood as the recombination of less reactive photogenerated carriers while preserving the highly reactive ones. However, the detailed interfacial electron transfer process can vary slightly among different S-scheme heterojunctions. Here we design a well-structured S-scheme covalent organic framework (COF)/TiO₂ heterojunction to explore its microscopic interfacial electron transfer processes. Notably, we identify a cross-interface secondary electron pumping phenomenon within the S-scheme heterojunction, leading to the formation of high-energy anti-Kasha excited states. This discovery deepens our understanding of the S-scheme charge transfer mechanism and suggests that the redox capabilities of S-scheme heterojunctions exceed traditional expectations. Our findings provide new insights into the origins of the high activity observed in S-scheme heterojunctions and enhance our understanding of their electron transfer processes.

Key words: High-energy excited state, Secondary electron pumping, S-scheme heterojunction, Hydrogen peroxide, Photocatalysis