Catalysts Designing Difference between Pure CO₂ and Diluted CO₂ Electro-Reduction: The Role of *CO Generation

The electrocatalytic reduction of industrially diluted CO₂ streams (5-30%) represents a pivotal avenue for carbon resource utilization. However, its practical implementation has long been hindered by mass transfer limitations and competitive hydrogen evolution reactions under low CO₂ concentrations. Current research has largely focused on pure CO₂ systems, overlooking the mechanistic intricacies of *CO intermediate dynamics and C-C coupling efficiency in CO₂-deficient environments. To address this challenge, this study developed compositionally tunable core-shell Ag@(Cu₂O)_x catalysts via a seed-mediated growth approach, enabling precise modulation of the Cu₂O/Ag ratio (x = 0.14-5.0) to optimize the interplay between *CO intermediates and C-C coupling under diluted conditions. Notably, experimental results demonstrate that the Ag-rich Ag@(Cu₂O)_0.75 catalyst achieves a Faradaic efficiency for ethylene (FE_C2H4) exceeding 45% under 25% CO₂. While the Cu₂O-rich Ag@(Cu₂O)_3.0 catalyst, although optimal in pure CO₂ systems, fails under the same diluted conditions due to insufficient *CO supply. This discovery underscores the pivotal role of *CO supply in dictating the overall catalytic efficiency and product distribution pathways during low-concentration CO₂ electrocatalytic processes.