(646a) Directing the Selectivity of CO2 Electroreduction Toward a Single C2 Product By Collective Control of Rate-Determining and Selectivity-Determining Steps

In CO₂ electroreduction, a crucial step of C-C coupling through dimerization of adsorbed *CO has been identified as the rate-determining step (RDS) for C₂₊ products formation over Cu-based catalysts. This phenomenon provides an opportunity to design cascade reactions through CO intermediate to improve the yield of C₂₊ products. Bimetallic tandem catalysts integrating Cu with a CO-generation metal were widely used to improve C-C coupling kinetics. 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. To further promote the selectivity toward a single product (e.g., C₂H₄), the Cu surface needs to be modified to tune the direction of selectivity-determining step following the C-C coupling reaction. 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.