摘要： Ultrathin Co0.85Se nanosheets were prepared via a facile solvothermal method, which successfully overcome the disadvantage of insu?cient active sites in bulk Co0.85Se by reducing its thickness into the atomic scale. Co0.85Se nanosheets have been found to be e?cient cocatalysts for photocatalytic CO2 reduction with TON as high as 58 in 1 h reaction under visible-light irradiation. Compared with bulk Co0.85Se blocks, the ultrathin nanosheet samples exhibited nearly 2.5 times higher activity in CO2 photoreduction. The metal-like character and ultrathin 2D structure of Co0.85Se nanosheets support the superb charges transfer and rich CO2 adsorption sites exposure for surface catalysis. A relationship between the surface structure and the cocatalytic activity was established. These results not only demonstrate the potential of a notable, a?ordable and earth-abundant CO2 photoreduction cocatalyst based on ultrathin Co0.85Se nanosheets but also provide a guidance in the exploration of excellent active and durable cocatalysts/catalysts to replace noble metals for arti?cial photosynthesis.