Electrochemical Reduction of CO₂ to CO by a Heterogeneous Catalyst of Fe–Porphyrin-Based Metal–Organic Framework

Abstract

Heterogeneous electrocatalysis provides better control of the chemical surroundings of the catalyst's active site for improved performance, offers the possibility of overcoming drawbacks of deactivation caused by aggregation or dimerization in homogeneous condition, and permits the use of benign aqueous solutions. Employing metal–organic frameworks (MOFs) or covalent–organic frameworks (COFs) to support the active molecular catalyst of porphyrin for electrochemical conversion of CO2 to CO is a promising strategy. We have rationally introduced a 3D highly stable porphyrin-based MOF of PCN-222(Fe) into heterogeneous catalysis through the simple dip-coating method. The composite catalyst PCN-222(Fe)/C (mass ratio = 1:2) exhibited high catalytic performance for electrochemical conversion of CO2 to CO with 494 mV overpotential (where j = 1.2 mA cm–2) and maximum 91% FECO in a CO2-saturated 0.5 M KHCO3 aqueous solution, achieving a TOF of 0.336 site–1 s–1. The catalyst was found to retain its crystallinity and stability after 10 h of electrolysis at −0.60 V versus RHE (average FECO 80.4%; RHE, reversible hydrogen electrode), which generates 334 μmol of CO with the TOF of 0.012 s–1 (0.286 site–1 s–1). These results indicate that the PCN-222(Fe)/C has a substantial catalytic effect on the electrochemical reduction of CO2 due to the combination of the intrinsic activity of the porphyrin molecule, and the promising CO2 adsorption ability endowed by the conserved porosity, as well as the high conductivity of carbon black.