Abstract: In transition metal oxides, introducing high concentrations of charge carriers can induce localized surface plasmon resonance (LSPR), akin to noble metals, thus broadening the photocatalyst's response spectrum. However, a lack of comprehensive theoretical understanding of LSPR limits its full exploitation in photocatalytic systems. In this study, we propose a strategy to regulate the hyper-release of LSPR in S-scheme heterojunctions. By leveraging Mie-Gans theory and hot electron transfer kinetics, we achieve a finely tuned balance between the trapping and release of LSPR-induced hot electrons through defect concentration optimization. Using femtosecond transient absorption spectroscopy, we distinguish LSPR-related signals in the infrared region and quantify the hot electron transfer efficiency in the heterojunction, providing compelling evidence for the hyper-release mechanism. An S-scheme heterojunction between monoclinic W₁₈O₄₉ and cubic CdS was constructed via an in-situ growth strategy without the use of noble metal co-catalysts, resulting in a composite that achieves an outstanding photocatalytic hydrogen evolution rate of 3125 µmol h^-1 g^-1, outperforming conventional designs. This work not only offers fresh insights into the electron dynamics of the LSPR effect but also sets a benchmark for designing plasmonic-semiconductor hybrid systems, opening new horizons for sustainable energy conversion technologies.

Key words: Localized surface plasmon resonance, Oxygen vacancy tuning, S-scheme heterojunction, Mie-Gans theory, Femtosecond transient absorption