Navigating the Selectivity Toward a Single C2 Product in CO2 Electroreduction

The rational design of gas diffusion electrodes (GDEs) and catalysts play a vital role in achieving the industrially relevant performance metrics (e.g., selectivity, productivity, stability, and energy efficiency) of CO₂ electroreduction for a specific C₂₊ product. Along the reaction pathway for C₂₊ products formation over Cu-based catalysts, a crucial step of C-C coupling through dimerization of adsorbed *CO or coupling of *CO with its hydrogenated derivatives (e.g., *CHO) has been identified by both experimental observation and theoretical calculation. This phenomenon provides an opportunity to design cascade reactions through CO intermediate to improve the yield of C₂₊ products. Some bimetallic tandem catalysts integrating Cu with a CO-generation metal (e.g., Ag and Au) have demonstrated the tandem catalysis effect, improving C-C coupling kinetics by increasing the partial pressure of CO (P_CO) near the Cu surface. However, when the tandem catalyst is applied in the conventional GDE comprising one homogeneous catalyst layer (CL), the CO utilization efficiency for C-C coupling is low because the local CO concentration throughout the CL is at the lowest level. Distinguished from the tandem catalysts, we introduce tandem electrodes, where the temporal and spatial CO concentration profiles are in-situ managed, to enhance the utilization of CO and thus drive cascade CO₂àCOàC₂₊ conversion with a yield at an industrial scale. We demonstrated that segmented tandem electrodes, even incorporating the commercial Cu nanoparticles, could reach over 90% Faradaic efficiency (FE) of C₂₊ products (60% FE for C₂H₄) at a partial current density of above 1 A cm^-2. We modulated the Cu surface by single-site doping to stabilize desired selectivity-determining intermediate, from which the formation of C₂H₄ versus C₂H₅OH branches. As a result, the selectivity toward C₂H₄ versus C₂H₅OH was controlled relatively. When the surface-modified Cu catalyst was integrated into the segmented tandem electrodes, the FE of C₂H₄ could be further increased to 70% at a partial current density of >1.5 A cm^-2. This presentation demonstrates the collective control of rate-determining and selectivity-determining steps to direct CO₂ conversion to a specific C₂ product at high production rates.