Unraveling the Intermediate Species of Co3O4 Hollow Spheres for CO2 Photoreduction by In Situ X-ray Absorption Spectroscopy

Nanostructured hollow materials have emerged as a promising class of materials for energy conversion and storage. In this work, we report a Co3O4 hollow sphere nanostructure that can serve as a CO2 reduction catalyst to form CO with high selectivity upon visible-light illumination in the presence of a [Ru(bpy)3]2+ molecular photosensitizer. Using in situ X-ray absorption spectroscopy, we not only showed that the Co center in the Co3O4 hollow sphere is the active site for CO2 reduction but also identified a key intermediate species, that is, a reduced Co center, due to electron transfer from the [Ru(bpy)3]2+ photosensitizer when the system can steadily generate CO.