Bionic Optical Leaf for Photoreduction of CO2 from Noble Metal Atom Mediated Graphene Nanobubble Arrays

The reduction of CO2 to useful chemicals by solar irradiation has been of great interest in recent years to tackle the greenhouse effect. Compared with inorganic metal oxide particles, carbonaceous materials, such as graphene, are excellent in light absorption; however, they lack in activity and selectivity because of the challenge to manipulate the band gap and optimize the electron-hole separation, which drives the photoreduction process. In this work, inspired by the delicate natural plant leaf structure, we fabricated orderly stacked graphene nanobubble arrays with nitrogen dopant for the coordination of noble metal atoms to mimic the natural photoreduction process in plant leaves. This graphene metamaterial not only mimics the optical structure of leaf cells, which scatter and absorb light efficiently, but also drives the CO2 reduction via nitrogen coordinated metal atoms as the chlorophyll does in plants. Our characterizations show that the band gap of nitrogen-doped graphene could be precisely tailored via substitution with different noble metal atoms on the doped site. The noble atoms coordinated on the doped site of graphene metamaterial not only enlarge the light absorption volume but also maximize the utilization of noble metals. The bionic optical leaf metamaterial coordinated with Au atoms exhibits high CO productivity up to 11.14 mmol gcat-1 h-1 and selectivity to 95%, standing as one of the best catalysts among the carbonaceous and metal-based catalysts reported to date. This catalyst also maintained a high performance at low temperatures, manifesting potential applications of this bionic catalyst at polar regions to reduce greenhouse gases.