Cu-Ag interactions in bimetallic Cu-Ag catalysts enhance C₂₊ product formation during electrochemical CO reduction

The electroreduction of CO (CORR) is a promising alternative to the direct CO₂ electroreduction reaction (CO2RR) to produce C₂₊ products. Cu-based electrocatalysts enable the formation of C-C bonds, leading to various C₂₊ hydrocarbon and oxygenate products. Herein, we investigated how the composition of bimetallic Cu-Ag catalysts impacted the nature of the Cu-Ag interactions and the product distribution of the CORR, aiming to improve the selectivity to C₂₊ products. Cu-Ag catalysts containing 1-50 mol% Ag were prepared by sol-gel synthesis. A Ag content of 10 mol% of Ag (Cu_0.9Ag_0.1) was optimum with respect to increasing the C₂₊ product selectivity and suppressing H₂ evolution. Operando X-ray absorption spectroscopy and quasi-in situ X-ray photoelectron spectroscopy demonstrated the complete reduction of CuO to Cu during CORR. Electron microscopy (EM) and in situ wide-angle X-ray scattering (WAXS) revealed substantial restructuring during reduction. EM imaging showed the formation of Ag-Cu core-shell structures in Cu_0.9Ag_0.1, while separate Cu and Ag particles were predominant at higher Ag content. In situ WAXS revealed the formation of a Cu-Ag nanoalloy phase in the bimetallic Cu-Ag samples. The optimum Cu_0.9Ag_0.1 sample contained more Cu-Ag nanoalloys than samples with a higher Ag content. The Cu-Ag interfaces between the Ag-core and the Cu-shell in the bimetallic particles are thought to host the nanoalloys. The optimum CORR performance for Cu_0.9Ag_0.1 is likely due to the enhanced Cu-Ag interactions, as confirmed by a sample prepared with the same surface composition by galvanic exchange.