The meso-substituent electronic effect of Fe porphyrins on the electrocatalytic CO2 reduction reaction

Abstract

We report Fe porphyrins bearing different meso-substituents for the electrocatalytic CO₂ reduction reaction (CO₂RR). By replacing two and four meso-phenyl groups of Fe tetraphenylporphyrin (FeTPP) with strong electron-withdrawing pentafluorophenyl groups, we synthesized FeF₁₀TPP and FeF₂₀TPP, respectively. We showed that FeTPP and FeF₁₀TPP are active and selective for CO₂-to-CO conversion in dimethylformamide with the former being more active, but FeF₂₀TPP catalyzes hydrogen evolution rather than the CO₂RR under the same conditions. Experimental and theoretical studies revealed that with more electron-withdrawing meso-substituents, the Fe center becomes electron-deficient and it becomes difficult for it to bind a CO₂ molecule in its formal Fe⁰ state. This work is significant to illustrate the electronic effects of catalysts on binding and activating CO₂ molecules and provide fundamental knowledge for the design of new CO₂RR catalysts.