Surface Chemistry Modulates CO2 Reduction Reaction Intermediates on Silver Nanoparticle Electrocatalysts

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.