Bimetallic Interface Control of Cu₂O Nanocrystals for Efficient CO₂-to-C₂₊ Chemical Conversion

Electrochemical carbon dioxide reduction reaction (CO₂RR) is promising in the pursuit of carbon neutrality, as it converts CO₂, the primary contributor to global warming, into valuable high-end fuels and chemical feedstocks. Copper (Cu) is the only metal that has an appropriate *CO binding energy for C-C coupling. Cu-based CO₂RR electrocatalysts can produce multi-carbon (C₂₊) chemicals such as ethylene, ethanol, and acetic acid. Nonetheless, they suffer from low selectivity for producing specific products. Particularly, bimetallic systems including Cu with secondary metals such as Au and Ag for their weak *CO bonds, emerge as a promising strategy to enhance the production of C₂₊ chemicals. However, the focus of Cu-based bimetallic catalysts has primarily been optimizing the ratio of secondary metals, overlooking the significance of interface control for efficient CO₂RR.<br/>In this study, we fabricated the facet-controlled Cu₂O nanocrystals (NCs) and studied the effect of bimetallic interface design on the CO₂RR. Cu₂O NCs includes cube with (100) facets, cuboctahedron (cubo) with (100) and (111) facets, and octahedron (octa) with (111) facets. We introduced Ag and Au as secondary metals to facet controlled Cu₂O NCs through galvanic replacement. Shape and size distributions of the secondary metal were affected by surface energy and the surface atomic diffusion rate. These factors proved to be pivotal in the fabrication of three distinct catalysts, each characterized by varying Cu-Ag, Cu-Au interfacial compositions. In general, Cu₂O cube with low-surface-energy exhibited segregation and agglomeration at the interfaces, whereas Cu₂O cubo and octa with high-surface-energy formed well-dispersed interfaces. Bare Cu₂O cube exhibited a 40% Faradaic efficiency (FE) for C₂₊ products and achieved H₂ FE of 19% at -0.73 V (vs RHE). Ag-augmented Cu₂O cube significantly improved selectivity by reaching 57% FE for C₂₊ and suppressing H₂ with a FE of 13% at -0.78 V (vs RHE). In contrast, the Au-augmented Cu₂O cube promoted H₂ with 25% FE and C₂₊ with 33% FE at -0.99 V (vs RHE), resulting in reduced performance. To gain deeper insights into the intermediate behavior of *CO, <i>in-situ</i> Raman spectroscopy was employed, highlighting the critical importance of the metal effect in CO₂RR. Remarkably, it was observed that CO derived from Ag had a more pronounced impact on increasing *CO coverage on the Cu surface compared to that of Au. Furthermore, the relatively higher portion of high-frequency band (HFB) *CO_atop represents efficient C-C coupling. This study sheds light on the bimetallic interface design of Cu-based active sites for efficient C₂₊ chemical production in CO₂RR.