The Importance of Ligand Coverage on Nanocatalysis: Optimizing CO₂ Electroreduction Activity on Pyridine Modified...

Ligand retention or modification at the surfaces of nanocatalysts can modulate catalytic performance, but the role of ligand coverage is often underappreciated. Herein, we systematically investigate the effect of pyridine ligand coverage on the electrocatalytic CO₂ reduction reaction (CO₂RR) of gold (Au) nanoparticles. An optimal pyridine coverage (θ = 55%) yields maximal CO₂RR performance, with a CO Faradaic efficiency of ∼100% and a CO mass activity of 1.11 A mg^-1. Combined physical characterization, in situ electrochemical infrared spectroscopy, and theoretical calculations reveal that increasing pyridine coverage progressively renders the Au surface more negatively charged. The elevated surface electron density alters the interfacial water structure from isolated H₂O to strongly hydrogen-bonded networks, facilitating formation of the key *COOH intermediate. Concurrently, the electron-rich Au surface weakens CO adsorption, promoting CO desorption and thereby enhancing both activity and selectivity toward CO. The optimal pyridine coverage represents a balance between electronic promotion of intermediate formation and steric effects of the ligand, enabling concurrently favorable *COOH generation and CO desorption. These findings establish ligand coverage as a critical parameter for tuning nanocatalyst behavior and suggest that coverage optimization may be broadly applicable across catalytic systems.