Ionic Liquid-Modified Porous Organometallic Polymers as Efficient and Selective Photocatalysts for Visible-Light-Driven CO 2 Reduction

Abstract

In the photoreduction of CO 2 to CO, the competitive H 2 evolution is always inevitable due to the approximate reduction potentials of H + /H 2 and CO 2 /CO, which results in poor selectivity for CO production. Herein, imidazolium-type ionic liquid- (IL-) modified rhenium bipyridine-based porous organometallic polymers (Re-POMP-IL) were designed as efficient and selective photocatalysts for visible-light CO 2 photoreduction to CO based on the affinity of IL with CO 2 . Photoreduction studies demonstrated that CO 2 photoreduction promoted by Re-POMP-IL functioning as the catalyst exhibits excellent CO selectivity up to 95.5% and generate 40.1 mmol CO/g of Re-POMP-IL1.0 (obtained by providing equivalent [(5,5 ′ -divinyl-2,2 ′ -bipyridine)Re(CO) 3 Cl] and 3-ethyl-1-vinyl-1 H -imidazol-3-ium bromide) at 12 h, outperforming that attained with the corresponding Re-POMP analogue without IL, which highlights the crucial role of IL. Notably, CO 2 adsorption, light harvesting, and transfer of photogenerated charges as key steps for CO 2 RR were studied by employing POMPs modified with different amounts of IL as photocatalysts, among which the CO 2 affinity as an important factor for POMPs catalyzed CO 2 reduction is revealed. Overall, this work provides a practical pathway to improve the CO 2 photoreduction efficiency and CO selectivity by employing IL as a regulator.