Single-atom modified graphene cocatalyst for enhanced photocatalytic CO2 reduction on halide perovskite

Metal halide perovskite (MHP) has become one of the most promising materials for photocatalytic CO₂ reduction owing to the wide light absorption range, negative conduction band position and high reduction ability. However, photoreduction of CO₂ by MHP remains a challenge because of the slow charge separation and transfer. Herein, a cobalt single-atom modified nitrogen-doped graphene (Co-NG) cocatalyst is prepared for enhanced photocatalytic CO₂ reduction of bismuth-based MHP Cs₃Bi₂Br₉. The optimal Cs₃Bi₂Br₉/Co-NG composite exhibits the CO production rate of 123.16 μmol g^–1 h^–1, which is 17.3 times higher than that of Cs₃Bi₂Br₉. Moreover, the Cs₃Bi₂Br₉/Co-NG composite photocatalyst exhibits nearly 100% CO selectivity as well as impressive long-term stability. Charge carrier dynamic characterizations such as Kelvin probe force microscopy (KPFM), single-particle PL microscope and transient absorption (TA) spectroscopy demonstrate the vital role of Co-NG cocatalyst in accelerating the transfer and separation of photogenerated charges and improving photocatalytic performance. The reaction mechanism has been demonstrated by in situ diffuse reflectance infrared Fourier-transform spectroscopy measurement. In addition, in situ X-ray photoelectron spectroscopy test and theoretical calculation reveal the reaction reactive sites and reaction energy barriers, demonstrating that the introduction of Co-NG promotes the formation of *COOH intermediate, providing sufficient evidence for the highly selective generation of CO. This work provides an effective single-atom-based cocatalyst modification strategy for photocatalytic CO₂ reduction and is expected to shed light on other photocatalytic applications.