Elucidating the Donor/Acceptor Regulatory Mechanism for CO 2 Electroreduction

Abstract Catalysts with Cu─N x active sites have shown promising performance in the electrochemical CO 2 reduction reaction (CO 2 RR), but it remains elusive to systematically modulate their CO 2 RR activity. Herein, a series of substituted copper phthalocyanines (CuPc‐R) with various electron‐withdrawing/donating groups are designed to study the relationship between the CO 2 RR activity and the electron density at the Cu─N 4 center. Notably, a positive shift of +0.27 V for the reduction potential of phthalocyanine ligands is observed by changing substituents from electron‐donating to stronger electron‐withdrawing effect (correlated to increasing Hammett constant), owing to the decreasing electron density of phthalocyanines center. Their CO 2 RR‐to‐CH 4 activity displays approximately a linear relationship with the Hammett constant, while CuPc‐Cl 4, with the strongest electron‐withdrawing substituent, shows the maximum FE CH4 of 73.7% and related j CH4 of −147.4 mA cm −2 . The DFT calculations and in situ spectroscopic characterizations illustrate that the decreased electron density of the Cu─N 4 center via strong electron‐withdrawing groups for CuPc‐R contributes to the reduced hydricity for restricted HER activity, thus promoting the CH 4 selectivity.