Alkali metal cation effects on electrocatalytic CO2 reduction with iron porphyrins

The electrocatalytic CO2 reduction reaction (CO2RR) has attracted increasing attention in recent years. Practical electrocatalysis of CO2RR must be carried out in aqueous solutions containing electrolytes of alkali metal cations such as sodium and potassium. Although considerable efforts have been made to design efficient electrocatalysts for CO2RR and to investigate the structure–activity relationships using molecular model complexes, only a few studies have been investigated the effect of alkali metal cations on electrocatalytic CO2RR. In this study, we report the effect of alkali metal cations (Na+ and K+) on electrocatalytic CO2RR with Fe porphyrins. By running CO2RR electrocatalysis in dimethylformamide (DMF), we found that the addition of Na+ or K+ considerably improves the catalytic activity of Fe chloride tetrakis(3,4,5-trimethoxyphenyl)porphyrin (FeP). Based on this result, we synthesized an Fe porphyrin N18C6-FeP bearing a tethered 1-aza-18-crown-6-ether (N18C6) group at the second coordination sphere of the Fe site. We showed that with the tethered N18C6 to bind Na+ or K+, N18C6-FeP is more active than FeP for electrocatalytic CO2RR. This work demonstrates the positive effect of alkali metal cations to improve CO2RR electrocatalysis, which is valuable for the rational design of new efficient catalysts.