Precise Tuning of Functional Group Spatial Distribution on Porphyrin Rings for Enhanced CO2 Electroreduction Selectivity

Abstract

Molecular catalysts play a critical role in regulating the selectivity of electrocatalytic CO2 reduction reaction (CO2RR), yet the understanding of ligand function is largely restricted to modulating the electronic structure of the metal and reaction kinetics. Herein, a hydroxyl (-OH) ligand is introduced into a sterically hindered amino-porphyrin (o-TAPP) to synthesize the atropisomers porphyrin- salicylimine-Cu (o-Cu-Por-Sa) with hydrogen-bonding interactions (O-H···O), enabling efficient selection of CO and CH4 under dual effects. Detailed analysis shows that the -OH of o-Cu-Por-Sa (αβαβ) forms a noncovalent hydrogen bond with carbonate, characterized by a bond length of 2.01 Å and an angle of 27.6°, and this interaction reduces the reaction energy barrier, achieving a Faradaic efficiency (FE) of 84% for CH4. Moreover, the steric hindrance effect of the symmetric distribution of -OH facilitates protonation reactions by preventing C-C coupling. In contrast, -OH aggregated on o-Cu-Por-Sa (αααα) forms a pocket-like hydrogen bond grid, which restricts free CO2 adsorption and the rapid dissociation of *CO also interrupts the reaction. This work highlights the pivotal role of dual effects induced by ligand atropisomerization in regulating selectivity, offering new insights for the design of efficient molecular catalysts.