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.