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

Abstract

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.