Abstract
<jats:p>Cu–N–C molecular catalysts with well-defined Cu–N4 sites show strong potential for CO2-to-CH4 production, yet the role of the macrocyclic backbone remains unclear. Herein, we compare two representative Cu–N–C molecular catalysts, copper phthalocyanine (CuPc) and copper tetraphenylporphyrin (CuPr), to clarify how the macrocyclic backbone influences CO2-to-CH4 electrocatalysis. When supported on conductive carbon and integrated into gas-diffusion electrodes, CuPc markedly outperforms CuPr, achieving a CH4 Faradaic efficiency of 79.5%, a high partial current density of -575 mA cm-2, a mass activity of 19,166.7 A g-1, and stable operation for over 80 h at -150 mA cm-2. Characterization results suggest that the Pcmacrocyclic backbone modulates the electronic structure of the Cu center and interfacial charge-transfer behavior, possibly through its extended π-conjugated Pc-ring and bridge-N environment. Theoretical calculations reveal a favorable CH4-forming pathway on the CuPc/C model, with a lower free-energy barrier for the potential-determining step than that reported for CuPr, suggesting facilitated CH4 formation. These findings indicate that the macrocyclic backbone can regulate reaction pathways and intermediate adsorption energetics, providing mechanistic insight and design guidance for molecular catalysts for CO2-to-CH4 electroreduction.</jats:p>