Theoretical calculations and experimental verification of carbon dioxide reduction electrocatalyzed by metalloporphyrin.

Metal-functionalized porphyrin-like graphene structures are promising electrocatalysts for carbon dioxide reduction reaction (CORR) as their metal centers can modulate activity. Yet, the role of metal center of metalloporphyrins (MTPPs) in CO reaction activity is still lacking deep understanding. Here, CORR mechanism on MTPPs with five different metal centers (M = Fe, Co, Cu, Zn and Ni) are examined by first-principles calculations. The *COOH formation is the rate determined step on the five MTPP structures, and the CoTPP exhibits the best CORR activity while ZnTPP and NiTPP are the worst, which is also verified by our experiment. The CORR activity is controlled by adsorption states of intermediates (*CO, *COOH), i.e., chemisorption (e.g., on CoTPP) and physisorption (on ZnTPP and NiTPP) of intermediates will lead to good and poor activity, respectively. The deeper the d-band center of the porphyrin ring complexed metal atom, the weaker bonding of MTPP with CO and COOH. Theoretical calculations and experimental results indicate that MTPPs with Co and Fe centers lead to a reduction in the energy barriers for the two uphill reaction steps in the electrocatalytic CO reduction process, thereby enhancing CO reduction electrocatalytic activity. Faradaic efficiency of CO is correlated with the reaction energy barrier of the first proton-coupled electron reduction process, displaying a strong linear correlation. This work provides a fundamental understanding of MTPPs used as electrocatalysts for CORR.