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Exploring high-efficiency photocatalysts for selective CO2reduction is still challenging because of the limited charge separation and surface reactions. In this study, a noble-metal-free metallic VSe2nanosheet was incorporated on g-C3N4to serve as an electron capture and transfer center, activating surface active sites for highly efficient and selective CO2photoreduction. Quasi in situX-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and femtosecond transient absorption spectroscopy (fs-TAS) unveiled that VSe2could capture electrons, which are further transferred to the surface for activating active sites. In situdiffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations revealed a kinetically feasible process for the formation of a key intermediate and confirmed the favorable production of CO on the VSe2/PCN (protonated C3N4) photocatalyst. As an outcome, the optimized VSe2/PCN composite achieved 97% selectivity for solar-light-driven CO2conversion to CO with a high rate of 16.3 µmol·g–1·h–1, without any sacrificial reagent or photosensitizer. This work offers new insights into the photocatalyst design toward highly efficient and selective CO2conversion.