Nanoengineering Interfacial Reconstruction in Cu₂O@SiO₂ Catalysts to Tune C–C Coupling and Deep Hydrogenation in CO₂ Electroreduction

Electrochemical CO₂ reduction offers a promising route for converting CO₂ into value-added chemicals and fuels; however, switching selectivity between C₂₊ and CH₄ pathways by controlling interfacial reconstruction remains challenging. Herein, we report a simple and effective interface engineering strategy to address this issue. By tuning the thickness of the silica shell on Cu₂O catalysts, the reaction pathway can be steered toward either C₂₊ products or CH₄. Two distinct core–shell catalysts, Cu₂O@tn-SiO₂ (with a thin silica shell) and Cu₂O@tk-SiO₂ (with a thick silica shell), were synthesized using a wet-chemical method with controlled ammonia addition. For Cu₂O@tn-SiO₂, the thin SiO₂ shell facilitates the formation of a Cu/Cu₂O/SiO₂ three-phase interface upon pre-reduction, favoring asymmetric coupling of *CO and *CHO intermediates and enabling C₂₊ production, with a maximum C₂₊ current density of −675.1 mA cm^–2 and a faradaic efficiency (FE) of 80.9%. In contrast, the thick SiO₂ shell in Cu₂O@tk-SiO₂ stabilizes the Cu₂O/SiO₂ interface, suppresses extensive reconstruction, and modulates the local availability and transfer of hydrogen species through Si–O–H containing interfacial sites, thereby favoring selective hydrogenation of *CHO toward CH₄ with a peak partial current density of −464.4 mA cm^–2 and an FE of 61.9%. Mechanistic studies support that the silica shell enhances structural stability, regulates intermediate adsorption, and tunes the interfacial hydrogen/water environment, collectively contributing to the observed switch in reaction pathway. This work provides a straightforward and effective strategy for designing copper-based catalysts with tunable product selectivity for practical CO₂ electroreduction.