“Cu–N_x” Site-Driven Selectivity Switch for Electrocatalytic CO₂ Reduction

The comprehensive understanding of the effect of the chemical environment surrounding active sites on the pathway for the electrochemical carbon dioxide reduction reaction (eCO 2 RR) is essential for the development of advanced catalysts for large-scale applications. Based on a series of model catalysts engineered by the coordination of copper ions with various isomers of phenylenediamine [i.e., o -phenylenediamine ( o PD), m -phenylenediamine ( m PD), and p -phenylenediamine ( p PD)] featuring two amino groups in ortho -, meta -, and para -positions, the steric effects could significantly govern the selectivity of the “Cu–N” sites for eCO 2 RR. It was found the steric distance between adjacent copper and nitrogen active sites in Cu- o PD enhanced the C–C coupling of the *COOH intermediate, thereby resulting in increased selectivity for C 2 H 4 production. In contrast, the weak van der Waals interactions arising from steric electrostatic effects surrounding the *CHO intermediate on Cu- p PD facilitated subsequent hydrogenation, leading to the preferential synthesis of CH 4 . However, Cu- m PD exhibited diminished eCO 2 RR activity due to a higher free energy associated with the rate-determining step, which primarily led to the formation of H 2 . This study underscores the significant role of a steric effect-driven selectivity switch for eCO 2 RR.