Amorphization-Induced d-Orbital Rearrangement in Ultrathin CoO Nanosheets with Strong d-p Interactions for Efficient CO₂ Photoreduction.

Abstract

Photocatalytic CO₂ conversion into syngas presents a sustainable avenue for mitigating carbon emissions while generating value-added fuels. However, sluggish charge carrier dynamics and weak, non-specific interactions between catalytic sites and CO₂ molecules limit efficiency. Herein, ultrathin amorphous CoO nanosheets (a-CoO) are reported that integrate structural and electronic advantages for enhanced CO₂ photoreduction. X-ray absorption spectroscopy and density functional theory analyses reveal that amorphization partially transforms the local crystal field of Co from quasi-octahedral to quasi-tetrahedral coordination, resulting in a greater population of unpaired electrons in the frontier d-orbitals. This reconfiguration promotes electron injection from Co 3d_yz into the 2π* antibonding orbitals component of C 2p_x in CO₂, which strengthens 3d-2p orbital hybridization and lowers the activation energy barrier. In situ spectroscopic further confirms that this orbital restructuring accelerates charge transfer from the Co center to CO₂ and facilitates its activation. Meanwhile, the ultrathin 2D architecture improves the separation and transport of photoexcited carriers. Consequently, vigorous bubbles are observed under visible light irradiation, with a total syngas evolution rate of 23.7 mmol g^-1 h^-1 (12.6 and 11.1 mmol g^-1 h^-1 for CO and H₂, respectively) and an apparent quantum efficiency of 1.28% at 450 nm-≈8.7-fold improvement over its crystalline counterpart.