Visualizing interfacial charge transfer of two-dimensional heterostructure photocatalyst for efficient CO2 photoreduction via in situ spectroscopies

Photocatalytic CO₂ reduction into value-added chemicals holds significant promise for carbon–neutral recycling and solar-to-fuel conversion. Enhancing reaction efficiency by manipulating charge transfer is a key approach to unlocking this potential. In this work, we construct a two-dimensional/two-dimensional (2D/2D) FeSe₂/protonated carbon nitride (FeSe₂/PCN) heterostructure to promote the interfacial charge transfer dynamics, leading to a four-fold improved conversion efficiency of photocatalytic CO₂ reduction with near 100% CO selectivity. Combining in situ X-ray photoelectron spectroscopy, in situ soft X-ray absorption spectroscopy, and femtosecond transient absorption spectroscopy, it is revealed that FeSe₂ acts as an electron acceptor upon photoexcitation, introducing an additional electron transfer pathway from PCN to FeSe₂ that suppresses radiative recombination and promotes charge transfer. In situ X-ray absorption fine structure spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory calculation further unravel that the electron-enriched FeSe₂ functions as the active sites for CO₂ activation and significantly reduces the energy barrier of key intermediate COOH* formation, which is the rate-determined step for CO generation. This work underscores the importance of regulating photocarrier relaxation pathways to achieve effective spatial charge separation for promoted photocatalytic CO₂ reduction and demonstrates the powerful functions of in situ spectroscopies in in-depth understanding of the photocatalytic mechanism.