Importance of local coordination microenvironment in regulating CO₂ electroreduction catalyzed by Cr-corrole-based...

Single-atom catalysts (SACs) with MN₄ active sites are a promising type of electrocatalyst for CO₂ reduction reactions (CO₂RR). Here, we designed a novel corrole-based CO₂RR single-atom catalyst Cr-N₄-Cz with a metal center supported by conjugated N₄-macrocyclic ligand of corrole, which can serve as an excellent model for regulating the active center microenvironment, thereby achieving the goal of regulating the catalytic activity and selectivity. Density functional theory (DFT) calculations are performed to investigate the stability of Cr-N₃X-Cz (X = N, C, O, S, P) and the mechanism of local coordination microenvironment regulating catalytic selectivity. The calculation results show that Cr-N₄-Cz demonstrates high electrocatalytic activity for CO₂RR with a limiting potential of -0.25 V, and the main product is CO. However, the selectivity of CO₂RR is compromised due to the low limiting potential (-0.28 V) of the competitive hydrogen evolution reaction (HER). By substituting one N atom of Cr-N₄-Cz with C, O, S and P, the corresponding main products become HCOOH, CO, CO, and CH₃OH (or CH₄). Moreover, the competing HER reaction is suppressed, thus remarkably increasing the selectivity of electrocatalytic CO₂RR. Further mechanism investigation reveals different atomic substitution alters local coordination microenvironment of Cr metal center, resulting in the rising of d-orbital center and stabilizing the key intermediates of the potential determining step (PDS) by enhancing the integrated crystal orbital Hamilton population (ICOHP) between Cr and adsorbed intermediates, thereby regulating the CO₂RR process. Especially, P substitution improves charge transfer, thus facilitating hydrogenation CO₂ to form CH₃OH (or CH₄) in CO₂RR.