Mechanistic Elucidation of Excitation-Wavelength-Dependent Deactivation of a Water-Splitting Photocatalyst Using Operando Surface Spectroscopy

We elucidate the origin of visible-light inactivity in a Rh,Sb co-doped SrTiO3 photocatalyst loaded with Rh/Cr2O3 and CoOOH cocatalysts. Although the photocatalyst absorbs both UV and visible light, water splitting occurs only under UV-light irradiation. Operando soft X-ray absorption spectroscopy reveals the valence state of the CoOOH cocatalyst surface, which serves as the oxygen evolution reaction (OER) site. Under UV-light irradiation, oxidation of the CoOOH surface is observed, indicating transfer of photoinduced holes and promotion of the OER. In contrast, visible-light irradiation induces reduction of the CoOOH surface, demonstrating preferential electron transfer and suppression of the OER. Further analyses indicate that this excitation-wavelength-dependent reversal in carrier transfer originates from localization of photoinduced holes at Rh dopant sites under visible-light excitation. These results establish that excitation-wavelength-dependent carrier dynamics critically govern photocatalytic performance and underscore the necessity of rational dopant selection and band engineering for efficient visible-light-driven water splitting.