Enlarging the π-Conjugation of Cobalt Porphyrin for Highly Active and Selective CO2 Electroreduction

Heterogeneous molecular catalysts have attracted considerable attention as carbon dioxide reduction reaction (CO2RR) electrocatalysts. The pi-electron system of conjugated ligands in molecular catalysts may play an important role in determining the activity. In this work, by enlarging pi-conjugation through appending more aromatic substituents on the porphyrin ligand, altered pi-electron system endows the as-prepared 5,10,15,20-tetrakis(4-(pyren-1-yl)phenyl)porphyrin Co-II with high Faradaic efficiency (ca. 95 %) for CO production, as well as high turnover frequency (2.1 s(-1) at -0.6 V vs. RHE). Density functional theory calculation further suggests that the improved electrocatalytic performance mainly originates from the higher proportion of Co dz2 orbital and the CO2 pi* orbital in the HOMO of the (Co-porphyrin-CO2)(-) intermediate with larger pi-conjugation, which facilitates the CO2 activation. This work provides strong evidence that pi-conjugation perturbation is effective in boosting the CO2RR.