Electrocatalytic reduction of carbon dioxide (CO2R) to fuels and chemicals is a pressing scientific

and engineering challenge that is, in part, hampered by a lack of understanding of the surface reaction

mechanism, even for relatively simple systems. While many efforts have been dedicated to promoting CO2R

on catalytic surfaces by tuning composition, morphology, and defects, the role of the reaction environment

around the active site, and how this can be leveraged to modulate CO2R, is less clear. To this end, we

focused on a model CO2R catalyst, Ag nanoparticles, and carried out a combined electrocatalytic and

operando Raman spectroscopic investigation of CO2R on their surfaces. Bare Ag and chemically modified

Ag nanoparticles were investigated to understand how the surface reaction environment dictates

intermediate binding and catalytic efficiency en route to CO generation. The results revealed that the

primary product on Ag is CO, which is formed through a doubly-bound CObridge configuration. In contrast,

electrografted imidazole and polyvinylpyrrolidone (PVP)-coated Ag feature CO in a singly-bound COatop

configuration on their surfaces, whereas porous zeolitic-imidazolate framework-coated Ag was observed

to bind both CObridge and COatop. Further, another function of the Ag surface modifications is to dictate the

type of Ag surface sites which form Ag-C bonds with CO2R intermediates. Through analysis of the of

electrochemical and spectroscopic data, we deduce which key aspects of CO2R on Ag surface render a

CO2R system efficient and show how surface chemistry dictates diverging CO2R surface reaction

mechanisms. The insights gained here are important as they provide the community with a greater

understanding of heterogeneous CO2R and can be further translated to a number of catalytic systems.

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