A copper-based salphen organic framework with electron-donating groups for electrochemical carbon dioxide reduction to methane

Regulating the electronic structure of copper (Cu) active sites is an effective means to improve the electrochemical carbon dioxide reduction (ECO 2 R) performance of Cu single-site catalysts. However, the effect of specific functional groups on the electronic structure of Cu sites in Cu-based catalysts is unknown. In this paper, a novel electron-donating –OCH 3 modified Cu-based Salphen organic framework (Cu-SOF) with the Cu-N 2 O 2 configuration was synthesized by the Schiff base reaction. The –OCH 3 groups served as electron donors to induce electron transfer toward the Cu site, which improved the electrochemical CO 2 reduction (ECO 2 R) performance of Cu-SOF–OCH 3 . In the flow cell, the ECO 2 R evaluation results of Cu-SOF–OCH 3 showed that the Faradaic efficiency of CH 4 reached 65.9% at −1.2 V, which was superior to the similar catalysts reported in literatures. Further theoretical calculations showed that the HOMO-LUMO gap of Cu-SOF–OCH 3 was lower than that of Cu-SOF-H, which accelerated the electron transfer between the Cu site and the CO 2 molecule. Notably, Cu-SOF–OCH 3 exhibited a lower energy barrier in the process of generating *COOH and *CHO than Cu-SOF without the –OCH 3 group, which promoted the CH 4 formation.