Cu-based bimetallic catalysts for electrochemical CO₂ reduction: before and beyond the tandem effect

Electrochemical CO₂ reduction reaction (CO₂RR) is a promising approach for carbon reduction and the production of high-value chemicals. Among the various catalysts, Cu-based bimetallic catalysts have recently attracted significant attention due to their superior catalytic activity, often outperforming pure Cu counterparts, owing to the discovery of the tandem effect. This review provides an in-depth discussion of the development of Cu-based bimetallic catalysts for CO₂RR over the past decades, with the discovery, understanding, and evolution of the tandem effect serving as the central thematic thread. Important milestone works have been reviewed and organized in a roughly historical manner to highlight the development of cutting-edge understanding and the remaining challenges in this field. We believe this review will help the research community clearly track the progress from the original to the latest findings and identify key insights for Cu-based bimetallic catalysts for CO₂RR.