Rational Design of FeNi Bimetal Modified Covalent Organic Frameworks for Photoconversion of Anthropogenic CO2 into Widely Tunable Syngas.

Direct photoconversion of low-concentration CO2 into a widely tunable syngas (i.e., CO/H2 mixture) provides a feasible outlet for the high value-added utilization of anthropogenic CO2 . However, in the low-concentration CO2 photoreduction system, it remains a huge challenge to screen appropriate catalysts for efficient CO and H2 production, respectively, and provide a facile parameter to tune the CO/H2 ratio in a wide range. Herein, by engineering the metal sites on the covalent organic frameworks matrix, low-concentration CO2 can be efficiently photoconverted into tunable syngas, whose CO/H2 ratio (1:19-9:1) is obviously wider than reported systems. Experiments and density functional theory calculations indicate that Fe sites serve as the H2 evolution sites due to the much stronger binding affinity to H2 O, while Ni sites act as the CO production sites for the higher affinity to CO2 . Notably, the widely tunable syngas can also be produced over other Fe/Ni-based bimetal catalysts, regardless of their structures and supporting materials, confirming the significant role of the metal sites in regulating the selectivity of CO2 photoreduction and providing a modular design strategy for syngas production.