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

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.