Nanoconfinement Effects of Yolk–Shell Cu₂O Catalyst for Improved C₂₊ Selectivity and Cu⁺ Stability in Electrocatalytic CO₂ Reduction

Electrocatalytic conversion of carbon dioxide (CO₂) to value-added hydrocarbon products provides an industrially viable approach to utilizing carbon resources and the storage of renewable energy. Monovalent copper (Cu⁺) has been demonstrated to be indispensable for the formation of C₂₊ products via C–C coupling. However, the C₂₊ selectivity and stability of Cu⁺ at the cathodic potential remain a great challenge. In this work, we investigated the electrochemical properties of three Cu-based catalysts with different structures in the electrocatalytic reduction of the CO₂ reaction (eCO₂RR). Results showed that a Cu₂O catalyst with a yolk–shell microstructure having a distance between the shell internal surface and the core external surface of 25 nm displays the best performance. It exhibits a C₂₊ Faradaic efficiency of 80.2% and a FE_C2+ to FE_C1 ratio of ∼8.9. Both in situ ATR-SEIRAS and ex situ XPS characterization results reveal that Cu⁺ is stable under the experimental conditions, and the coverage of adsorbed carbon monoxide (*CO) on the Cu⁺ active site is enhanced due to nanoconfinement effects. The increased *CO surface coverage significantly promotes C–C coupling, leading to enhanced C₂₊ selectivity.