How does the ligands structure surrounding metal-N4 of Co-based macrocyclic compounds affect electrochemical reduction of CO2 performance?

Metal-Nx-C based materials have emerged as one of the most promising electrocatalysts for electrochemical reduction of carbon dioxide (ERCD). Co-based macrocyclic compounds have shown unique performance, however, of which the relationship between the ligands structure surrounding Co–N4 centers and reaction mechanism remains vague. To explore this issue, here, a series of Co-based macrocyclic compounds are elaborately chosen as model catalysts, including phthalocyanine cobalt (CoPc), cobalt (II) meso-Tetraphenylporphine (CoTp) and cobalt tetramethoxyphenylporphyrin (CoTop), which possess well-defined Co-N4 coordinated centers but different ligands structure surrounding Co-N4. Electrochemical measurements show that CoPc possesses higher activity and selectivity for CO with Faradaic efficiency (FE) above 62% at −0.7 V (vs. RHE) relative to those of CoTp and CoTop. Combining density functional theory (DFT) calculations, it can be further confirmed that CoPc is more favorable for ERCD to CO due to the rapid formation of key intermediate COOH* and the desorption of CO, demonstrating that the structure of ligands (phthalocyanine) surrounding Co-N4 plays a crucial role in the high CO selectivity. It can be anticipated that an exclusive strategy will pave a new avenue for further understanding the ERCD mechanism of Co-Nx-C catalysts.