A flexible cofacial Fe porphyrin dimer as an extremely efficient and selective electrocatalyst for the CO2 to CO conversion in non-aqueous and aqueous media

Efficient and selective electrochemical reduction of CO2 is a promising approach for its conversion to high value-added chemicals and reducing its green-house effect. Unless a suitable catalyst is used, the reduction occurs at a high overpotential (eta) and generates versatile products. Here a novel flexible cofacial Fe perfluorinated porphyrin dimer, f-Fe2PD, was designed for the electrocatalytic CO2-to-CO conversion in nonaqueous and aqueous solutions. The f-Fe2PD showed the CO2-to-CO conversion starting at only eta = 0.15 V that is the lowest reported overpotential in a homogeneous CO2-saturated DMF/10% H2O/1.0 M PhOH solution. This eta value is 0.29 V lower than that (0.44 V) of the corresponding rigid cofacial Fe porphyrin dimer (r-Fe2PD). The f-Fe2PD exhibited extremely high turnover frequencies (log TOF) of 2.4 and 7.3 s(-1) at eta values of 0.26 and 0.46 V, respectively with >94% CO faradaic efficiency (FECO). Moreover, the dimer was immobilized on ketjen black carbon (KBC) and grafted on a glassy carbon (GC) surface to achieve efficient and selective CO2-to-CO conversion in neutral aqueous CO2-saturated NaHCO3 solutions (0.5 M, pH = 7.3) with high durability. f-Fe2PD/KBC@GC showed TOF values of 4.5 and 18.1 s(-1) with practical current densities of 3.1 and 12.8 mA cm(-2) at eta values of 0.26 and 0.46 V, respectively. These values, to the best of our knowledge, are the highest reported values achieved in aqueous solutions at such low and moderate eta values. Several post-operando measurements proved the integrity of the f-Fe2PD under the CO2-to-CO conversion conditions. The combination of activity, efficiency, durability, and selectivity of the f-Fe2PD particularly in aqueous solutions is promising for clean energy production.

Automated summary

Efficient and selective electrochemical reduction of CO2 is a promising approach for converting it into valuable chemicals and reducing its greenhouse effect. A novel flexible cofacial Fe perfluorinated porphyrin dimer was designed for electrocatalytic CO2-to-CO conversion, showing high efficiency and selectivity, particularly in aqueous solutions. The combination of activity, efficiency, durability, and selectivity of the dimer in aqueous solutions holds promise for clean energy production.