(449e) Revealing the Structural Evolution of Cu/Ag Composites during Electrochemical Carbon Dioxide/Monoxide Reduction

Electrochemical CO₂/CO reduction (CO₂R/COR) garners significant attention as a promising approach for sustainable chemical/fuel production. Cu/Ag bimetallic materials have shown promising selectivity towards multi-carbon products, but the structure of Cu/Ag catalysts, product distribution, and mechanisms in CO₂/CO electroreduction remains inconsistent. Hence, comprehending the catalyst structural evolution during the electrocatalytic process is crucial for establishing robust structure/performance correlations for future catalysts design. Herein, we interrogate the structural evolution of a promising Cu-Ag oxide catalyst precursor during COR (>90% C₂₊ products). By using extensive in situ and ex situ characterization techniques, we reveal that the homogenous oxide precursors undergo a transformation to a bimetallic composite consisting of small Ag nanoparticles enveloped by thin layers (~2 nm) of amorphous Cu. By tuning the Cu/Ag ratio in the oxide precursor, we find that with the increase of Ag concentration, the coordination number and long-range order of Cu decreased during COR. We believe that the amorphous Cu layer with undercoordinated nature in Cu/Ag catalysts is responsible for the enhanced catalytic performance of the current catalyst composite. Increased Ag concentration also greatly promotes liquid products formation while suppressing the byproduct hydrogen. Specifically, at a modest potential of -0.47 V vs. reversible hydrogen electrode, Cu₃Ag₇ exhibits a high selectivity (>93%) towards multi-carbon products with over 60% being liquid products, at practical relevant current density of 200 mA cm^-2. CO₂/CO co-feeding electrolysis and isotopic labelling experiments suggest that high CO concentrations in the feed favors the formation of multi-carbon products, where the majority of C₂₊ products originated from the COR pathway. Overall, we anticipate the new insights obtained for Cu-Ag bimetallic systems for COR in this study can guide future catalyst design with improved performance.