Potential Alignment in Tandem Catalysts Enhances CO₂-to-C₂H₄ Conversion Efficiencies

The in-tandem catalyst holds great promise for addressing the limitation of low *CO coverage on Cu-based materials for selective C₂H₄ generation during CO₂ electroreduction. However, the potential mismatch between the CO-formation catalyst and the favorable C-C coupling Cu catalyst represents a bottleneck in these types of electrocatalysts, resulting in low tandem efficiencies. In this study, we propose a robust solution to this problem by introducing a wide-CO generation-potential window nickel single atom catalyst (Ni SAC) supported on a Cu catalyst. The selection of Ni SAC was based on theoretical calculations, and its excellent performance was further confirmed by using in situ IR spectroscopy. The facilitated carbon dimerization in our tandem catalyst led to a ∼370 mA/cm² partial current density of C₂H₄, corresponding to a faradic efficiency of ∼62%. This performance remained stable and consistent for at least ∼14 h at a high current density of 500 mA/cm² in a flow-cell reactor, outperforming most tandem catalysts reported so far.