Dynamic protonation of ligand sites in molecular catalysts enhances electrochemical CO₂ reduction

Molecular catalysts with functional group decorations are promising for electrocatalytic CO₂ reduction to produce valuable chemicals and fuels. Using nickel phthalocyanine derivatives with cyano, methoxy, and dimethylamino groups, this study unveils why decorating molecular catalysts with either electron-donating or electron-withdrawing groups can enhance their activity. Notably, the dimethylamino group-decorated catalyst demonstrated stable and nearly 100% CO₂-to-CO reduction selectivity over a wide potential range and high CO partial current densities up to 300 milliamperes per square centimeter. Theoretical and in situ spectroscopic analyses revealed the critical role of dynamic protonation of ligand sites in activating the metal center, which can be facilitated by the decoration of electron-withdrawing groups. Conversely, electron-donating groups, although requiring higher energy for protonation, enhance the synergy between metal centers and protonated sites, favoring the formation of key *COOH intermediates and improving CO selectivity at higher bias. This study underscores the importance of dynamic protonation of ligand sites in optimizing functionalized molecular catalysts for enhanced CO₂RR activity.