X-ray Absorption Spectroscopy Studies of a Molecular CO₂-Reduction Catalyst Deposited on Graphitic Carbon Nitride

Metal–ligand complexes have been extensively explored as well-defined molecular catalysts in small molecule activation reactions such as carbon dioxide (CO2) reduction. Many hybrid photocatalysts have been prepared by coupling such complexes with photoactive surfaces for use in solar CO2 reduction. In this work, we employ X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies, density functional theory (DFT) and computational XANES modeling to interrogate the structure of a hybrid photocatalyst consisting of a macrocyclic cobalt complex deposited on graphitic carbon nitride (C3N4). Results show that the cobalt complex binds on C3N4 through surface OH or NH2 groups. By refining the local geometry and binding sites of this well-defined molecular cobalt complex on C3N4, we established an important benchmark for modeling a large class of molecular catalysts that can be adapted to in situ/operando studies and further enhanced by applying chemometrics-based approaches and machine learning methods of XANES data analysis.