Co-porphyrin/Ru-pincer complex coupled polymer with Z-scheme molecular junctions and dual single-atom sites for visible light-responsive CO2 reduction

Abstract

• A new Co-porphyrin/Ru-pincer complex coupled polymer with efficient MMCT is prepared. • Periodic Z-scheme molecular junctions in the polymer promote the charge transfer. • Ru/Co centers in the polymer serve as the reduction/oxidation single-atom sites. • The polymer shows much better Vis-NIR light-driven CO 2 RR activity than its monomers. • A special CO 2 RR mechanism via a pincer-typed N′NN′-Ru-CO intermediate is proposed. Covalent organic polymer has been considered as the promising organic semiconductor for the photocatalytic CO 2 reduction reaction (CO 2 RR) due to its unique features such as adjustable framework, durable stability and feasible bandgap energy, et al . Herein, we report a novel Co II -porphyrin/Ru II -pincer complex coupled polymer (CoPor-RuN 3 ), which exhibits efficient visible light-responsive CO 2 RR activity with the average CO/CH 4 yields of 37.1/1.57 μmol g -1 h −1 and a total photoactivity of 86.8 μmol g -1 h −1 , 25.5 and 4.5 times that of the CoPor and RuN 3 monomers, respectively. It is found that the two metal centers (Co/Ru) and the conjugated framework of the polymer are essential for efficient CO 2 RR. A series of in-situ characterizations prove that periodic Z-scheme molecular junctions are formed by the linkage of amide group in the CoPor-RuN 3 polymer to facilitatie the photogenerated electron transfer from CoPor units to RuN 3 ones, in which Ru and Co serve as the reduction and oxidative single-atom sites, respectively. Moreover, the wavelet transform plots of X-ray absorption spectra of Ru K-edge shows that two CH 3 CN ligands are easily dissociated from the Ru center during the photocatalytic process, leaving empty sites for the adsorption of CO 2 . Based on the experimental observations and theoretical calculations, a plausible photocatalytic CO 2 reduction mechanism involving a pincer-typed N′NN′-Ru-CO intermediate (N′NN′ = 2,6-bis(benzimidazol-2-yl)pyridine) as the real reduction center is clarified. This work gives a new thread for exploring broadband-responsive covalent organic polymers with uniformly dispersed single-atom catalytic sites for CO 2 photoreduction.