Electron effect regulation: A study on the influence of electron-donating and withdrawing group modification on the performance of metal-coordinated catalysts for electrochemical carbon dioxide reduction.

Electron effect regulation is a crucial factor influencing the activity and selectivity of Cu-based coordination compound catalysts in the electrochemical carbon dioxide reduction reaction (CO2RR). Despite significant progress, the structure-activity relationship and the underlying regulatory mechanisms warrant further in-depth investigation. In this study, three types of Cu-[ONNO] tetradentate coordination molecular catalysts with varying electron densities, namely Cu-N2O2, methoxy-modified Cu-N2O2 (Cu-EDG-N2O2), and nitro-modified Cu-N2O2 (Cu-EWG-N2O2), were prepared using a substituent regulation strategy. The prepared catalyst's micromorphology and structural characteristics were analyzed using various characterization methods. Systematic electrocatalytic CO2RR experiments were conducted to evaluate the performance of these catalysts. Compared to the unmodified Cu-N2O2, the Cu-EDG-N2O2 catalyst exhibited superior reduction performance for CH4 and C2H4 products. At an applied potential of -1.7 V vs. the reversible hydrogen electrode, the Faradaic efficiencies for CH4 and C2H4 of Cu-EDG-N2O2 were 37.8 ± 2.2 % and 25.0 ± 0.5 %, respectively. In contrast, the Cu-EWG-N2O2 catalyst demonstrated higher activity towards the production of H2 as a by-product. The effects of electronic properties of substitutions on catalyst performance were revealed by combining experimental characterization and theoretical simulation. The results showed that the conjugation effect of the -OCH3 group facilitates faster electron transfer between Cu and CO2, thereby enhancing CO2RR activity. Additionally, the introduction of different substituents modulates the local microenvironment around the Cu active centers, significantly influencing the catalytic performance. This study provides valuable theoretical and experimental insights into the design of efficient Cu-N2O2-type metal coordination electrocatalysts for CO2RR processes.