Functional group engineering for boosting catalytic activity: high turnover frequency in electrocatalytic CO2 reduction and Zn-CO2 batteries.

Functionalized cobalt phthalocyanine (CoPc) supported on carbon supports are promising electrocatalyst for the electrochemical reduction of carbon dioxide (eCO2RR), yet the role of functional groups on catalytic activity is pending for clarification and optimization to maximize the reaction kinetics. Herein, a series of eCO2RR catalysts are fabricated by affixing functionalized molecular catalysts onto the nitrogen-doped porous carbon (NPC), denoted as CoPc-4x@NPC (x = H, NH2 and NO2). Among them, CoTNPc@NPC exhibits exceptional eCO2RR performance: in an H-type cell, it achieves a current density of 45 mA cm-2 at -0.91 V vs. RHE with CO Faradaic efficiency (FECO) exceeding 93.5% over a wide potential range, long-term stability over 40 h, and a remarkable turnover frequency (TOF) of 23.49 s-1. In a flow cell configuration, the CO partial current density (JCO) further increases to 224.1 mA cm-2 at -0.91 V. Density functional theory (DFT) calculations reveal that the nitro group upshifts the d-band center, enhances Co center electrophilicity, pre-donates electrons for *COOH formation, and underlies the higher turnover frequency. Integrating CoTNPc@NPC into a Zn-CO2 battery delivers a maximum discharge power density of 3.86 mW cm-2 and stable operation for over 15 h. This work highlights the potential of molecularly engineered CoPc catalysts for eCO2RR and Zn-CO2 battery applications, providing new insights for the rational design of high-performance electrocatalysts.