Enhancing CO2 Reduction Efficiency on Cobalt Phthalocyanine via Axial Ligation

Electrochemical reduction of carbon dioxide (CO2RR) to value-added products is a promising strategy to alleviate the greenhouse gas effect. Molecular catalysts, such as cobalt (II) phthalocyanine (CoPc), are known to be efficient electrocatalysts that are capable of converting CO2 into carbon monoxide (CO). Herein, we report an axial modification strategy to enhance CoPc’s CO2RR performance. After coordinating with axial ligands, the electron density of Co was depleted via π-backbonding. This π-backbonding weakened the Co-CO bond, resulting in rapid desorption of CO. Also, the presence axial ligands elevated the Co dz2 orbital energy, resulting in a significantly enhanced CO2 selectivity, evidenced by an increased faradaic efficiency (FE) from 82% (CoPc) to 91% (pyridine) and 94% (imidazole) at -0.82 V vs. RHE. Density functional theory calculations reveal that axial ligation of CoPc can reduce the energy barrier for CO2 activation and facilitate the formation of *COOH.