Stable and Exclusive Formation of CO from CO₂ Photoreduction with H₂O Facilitated by Linear Fluorene and Naphthalene Diimide-Based Conjugated Polymers

Abstract

Five conjugated polymers are synthesized, characterized, and examined in heterogeneous CO2 photoreduction with H2O. A promising CO production rate of 10.07 μmol g–1 h–1 is achieved with exclusive formation of CO in the absence of amine sacrificial agents. This photocatalytic system is highly stable. No significant degradation in the CO production rate is observed after 104 h of illumination. The physical and photocatalytic properties of the polymers are compared, revealing that the lowest unoccupied molecular-orbital energy could be the most significant factor in determining the conversion efficiency. On the other hand, CO2 might be trapped by the tetraalkylammonium bromide functionality installed in a polymer, hampering CO generation. The presence of water vapor improves the CO production rate. Density functional theory (DFT) calculations indicate that water molecules can reduce the Gibbs free energy difference for CO2 reduction to CO. This work demonstrates the use of linear conjugated polymers in the CO2 photoreduction and illuminates the working principles, paving the way for conversion of solar energy into useful fuels.

Solution-processable polymers of intrinsic microporosity for gas-phase carbon dioxide photoreduction

“…Triphenylamine based conjugated polymers have been shown to catalyse CO 2 to CO reduction using water vapour, at a rate of 37.15 μmol h −1 g −1 , with no added co-catalyst, and a quantum efficiency of 0.19% at 420 nm 30 . Similarly, naphthalene diimide conjugated polymers have demonstrated CO 2 photocatalysis in the gas phase, obtaining CO as the sole product 31 . However, in these cases stoichiometric oxygen or H 2 O 2 were not detected and so the exact oxidation reaction occurring is unclear.…”

Synthesis of 3,3’‐(Ethane‐1,2‐diylidene)bis(indolin‐2‐one) Promoted by Thermally‐activated Electron Transfer and Photoreduction of CO2 to CH4 and CO

“…Organic functionalities pyrene, [3] triazine, [4] benzothiadiazole, [4] cyclotriphosphazene, [5][6] triphenylamine, [7] oxadiazole, [7] eosin Y, [8] carbazole, [9] naphthalenedimide, [10][11] fluorene [10] phenanthraquinone, [12] and 1,3,5triphenylbenzene [13] have been used to build cross-linked or linear conjugated polymer catalysts (Scheme S1, Supporting Information). Among these polymeric photocatalysts, a pyrenebased polymer gave a CO product rate (R CO ) of 47.37 μmol g cat À 1…”