Surface Chemistry Modulates CO2 Reduction Reaction Intermediates on Silver Nanoparticle Electrocatalysts

Electrocatalytic reduction of carbon dioxide (CO2R) to fuels and chemicals is a pressing scientificand engineering challenge that is, in part, hampered by a lack of understanding of the surface reactionmechanism, even for relatively simple systems. While many efforts have been dedicated to promoting CO2Ron catalytic surfaces by tuning composition, morphology, and defects, the role of the reaction environmentaround the active site, and how this can be leveraged to modulate CO2R, is less clear. To this end, wefocused on a model CO2R catalyst, Ag nanoparticles, and carried out a combined electrocatalytic andoperando Raman spectroscopic investigation of CO2R on their surfaces. Bare Ag and chemically modifiedAg nanoparticles were investigated to understand how the surface reaction environment dictatesintermediate binding and catalytic efficiency en route to CO generation. The results revealed that theprimary 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 COatopconfiguration on their surfaces, whereas porous zeolitic-imidazolate framework-coated Ag was observedto bind both CObridge and COatop. Further, another function of the Ag surface modifications is to dictate thetype of Ag surface sites which form Ag-C bonds with CO2R intermediates. Through analysis of the ofelectrochemical and spectroscopic data, we deduce which key aspects of CO2R on Ag surface render aCO2R system efficient and show how surface chemistry dictates diverging CO2R surface reactionmechanisms. The insights gained here are important as they provide the community with a greaterunderstanding of heterogeneous CO2R and can be further translated to a number of catalytic systems.