Ligand-Modulated Release of Copper Active Sites Extends Ethylene Production in CO₂ Electroreduction

Copper catalysts for the electrochemical CO₂ reduction reaction (CO₂RR) undergo continuous reconstruction, causing a loss of ethylene selectivity over time. Here, we introduce a strategy based on molecular surface chemistry that prolongs the period of maximum ethylene production without sacrificing the activity of Cu electrocatalysts. First, we propose a customized synthesis of colloidal Cu nanocrystals to obtain comparable Cu catalysts differing only in the chemical nature of the organic surface ligand monolayer, thus acting as ideal model systems. Having discovered the unique behavior of secondary phosphines (PR₂H), we extend the proposed molecular strategy to commercial Cu, achieving a 10-fold increase in the operational stability of ethylene production. Operando spectroscopies combined with ex-situ microscopy correlate slower ligand desorption kinetics to delayed Cu reduction and restructuring, while atomistic simulations indicate that ligands do not intrinsically contribute to ethylene production. Altogether, surface ligands emerge as kinetic gatekeepers that sustain the generation of ethylene-selective active sites by modulating the Cu surface activation. This ligand-modulated activation concept provides a new design principle for possibly improving the long-term stability in electrocatalytic CO₂RR.