Potential Alignment in Tandem Catalysts Enhances CO-to-CH Conversion Efficiencies.

The in-tandem catalyst holds great promise for addressing the limitation of low *CO coverage on Cu-based materials for selective CH generation during CO 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/cm partial current density of CH, 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/cm in a flow-cell reactor, outperforming most tandem catalysts reported so far.