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

Abstract

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 (η) 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 η = 0.15 V that is the lowest reported overpotential in a homogeneous CO₂-saturated DMF/10% H₂O/1.0 M PhOH solution. This η 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 η values of 0.26 and 0.46 V, respectively with >94% CO faradaic efficiency (FE_CO). 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 η 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 η 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.