Active Site Concentration Steers the Reaction Pathway of CO2 Electroreduction
The local concentration and configuration of active sites critically influence the selectivity of CO2 electroreduction, yet constructing well-defined structures to probe this relationship remains challenging. Here, we report a molten salt-assisted strategy to synthesize Ce-Ov-Cu cascade catalysts with tunable configurations and relative concentrations of Cu and Ce-Ov sites. Two distinct geometries were engineered: one with dense Cu sites surrounding Ce-Ov (Cu10CeOx) and another with isolated Cu centers encapsulated by Ce-Ov (CuCe10Ox). These configurations direct key intermediates (*CHO or *COH) toward either C-C coupling or deep hydrogenation, thereby switching product selectivity. CuCe10Ox achieves a CH4 Faradaic efficiency (FE) of 61.7% at -1.6 V vs. RHE, whereas Cu10CeOx favors C2 production with a maximum FE of 61.5% at -1.4 V vs. RHE. Mechanistic studies reveal that locally concentrated Cu sites exhibit strong *CO2 binding affinity, enhancing *CO surface coverage and facilitating *CO-*COH coupling. In contrast, Ce-Ov-rich regions with isolated copper centers supply abundant *H, promoting deep protonation of *CHO toward CH4. This work provides insights into catalyst design, demonstrating that manipulating structural chemistry can guide CO2RR toward targeted products.