Nanoengineering Interfacial Reconstruction in Cu ₂ O@SiO ₂ Catalysts to Tune C–C Coupling and Deep Hydrogenation in CO ₂ Electroreduction

Electrochemical CO 2 reduction offers a promising route for converting CO 2 into value-added chemicals and fuels; however, switching selectivity between C 2+ and CH 4 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 Cu 2 O catalysts, the reaction pathway can be steered toward either C 2+ products or CH 4 . Two distinct core–shell catalysts, Cu 2 O@tn-SiO 2 (with a thin silica shell) and Cu 2 O@tk-SiO 2 (with a thick silica shell), were synthesized using a wet-chemical method with controlled ammonia addition. For Cu 2 O@tn-SiO 2, the thin SiO 2 shell facilitates the formation of a Cu/Cu 2 O/SiO 2 three-phase interface upon pre-reduction, favoring asymmetric coupling of *CO and *CHO intermediates and enabling C 2+ production, with a maximum C 2+ current density of −675.1 mA cm –2 and a faradaic efficiency (FE) of 80.9%. In contrast, the thick SiO 2 shell in Cu 2 O@tk-SiO 2 stabilizes the Cu 2 O/SiO 2 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 CH 4 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 CO 2 electroreduction.